Philipp Tomsich [Wed, 13 Sep 2017 19:29:35 +0000 (21:29 +0200)]
spl: atf: introduce spl_invoke_atf and make bl31_entry private
This adds a new interface spl_invoke_atf() that takes a spl_image_info
argument and then derives the necessary parameters for the ATF entry.
Based on the additional information recorded (into /fit-images) from
the FIT loadables, we can now easily locate the next boot stage.
We now pass a pointer to a FDT as the platform-specific parameter
pointer to ATF (so we don't run into the future headache of every
board/platform defining their own proprietary tag-structure), as
FDT access is already available in ATF.
With the necessary infrastructure in place, we can now update the
support for the ARM Trusted Firmware to dispatch into the
spl_invoke_atf function only if a IH_OS_ARM_TRUSTED_FIRMWARE image is
loaded.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Simon Glass <sjg@chromium.org>
Philipp Tomsich [Wed, 13 Sep 2017 19:29:34 +0000 (21:29 +0200)]
spl: fit: implement recording of loadables into /fit-images
If a FDT was loaded (e.g. to append it to U-Boot image), we store it's
address and record information for all loadables into this FDT. This
allows us to easily keep track of images for multiple privilege levels
(e.g. with ATF) or of firmware images preloaded into temporary
locations (e.g. PMU firmware that may overlap the SPL stage).
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Simon Glass <sjg@chromium.org>
Philipp Tomsich [Wed, 13 Sep 2017 19:29:33 +0000 (21:29 +0200)]
spl: fit: implement fdt_record_loadable
During the loading of more complex FIT images (e.g. when the invoked
next stage needs to find additional firmware for a power-management
core... or if there are multiple images for different privilege levels
started in parallel), it is helpful to create a record of what images
are loaded where: if a FDT is loaded for one of the next stages, it
can be used to convey the status and location of loadables.
This adds a fdt_record_loadable() function that can be invoked to
record the status of each loadable below the /fit-images path.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Simon Glass <sjg@chromium.org>
Philipp Tomsich [Wed, 13 Sep 2017 19:29:32 +0000 (21:29 +0200)]
spl: fit: simplify logic for FDT loading for non-OS boots
To better support bootin through an ATF or OPTEE, we need to
streamline some of the logic for when the FDT is appended to an image:
depending on the image type, we'd like to append the FDT not at all
(the case for the OS boot), to the 'firmware' image (if it is a
U-Boot) or to one of the loadables (if the 'firmware' is an ATF, an
OPTEE, or some other image-type and U-Boot is listed in the
loadabled).
To achieve this goal, we drop the os_boot flag and track the type of
image loaded. If it is of type IH_OS_U_BOOT, we append the FDT.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Acked-by: York Sun <york.sun@nxp.com> Reviewed-by: Simon Glass <sjg@chromium.org>
Philipp Tomsich [Wed, 13 Sep 2017 19:29:30 +0000 (21:29 +0200)]
spl: add a fdt_addr field to spl_image_info
When loading a full U-Boot with detached device-tree using the SPL FIT
backend, we should store the address of the FDT loaded as part of the
SPL image info: this allows us to fixup the FDT with additional info
we may want to propagate onward.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Simon Glass <sjg@chromium.org>
Philipp Tomsich [Wed, 13 Sep 2017 19:29:29 +0000 (21:29 +0200)]
image: add IH_OS_ARM_TRUSTED_FIRMWARE for ARM Trusted Firmware
To boot on ARMv8 systems with ARM Trusted Firmware, we need to
assemble an ATF-specific parameter structure and also provide the
address of the images started by ATF (e.g. BL3-3, which may be the
full U-Boot).
To allow us to identify an ARM Trusted Firmware contained in a FIT
image, this adds the necessary definitions.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Simon Glass <sjg@chromium.org>
Simon Glass [Mon, 13 Nov 2017 04:52:20 +0000 (21:52 -0700)]
binman: Set up 'entry' to permit full test coverage
There is a little check at the top of entry.py which decides if importlib
is available. At present this has no test coverage. To add this we will
need to import the module twice, once with importlib and once without.
In preparation for allowing a test to control the importing of this
module, remove all global imports of the 'entry' module.
Simon Glass [Mon, 13 Nov 2017 04:52:15 +0000 (21:52 -0700)]
buildman: Fix up tests
The tests were broken by two separate commits which adjusted the output
when boards are listed. Fix this by adding back a PowerPC board and
putting the name of each board in the test.
Fixes: b9f7d881 (powerpc, 5xx: remove some "5xx" remains) Fixes: 8d7523c5 (buildman: Allow showing the list of boards with -n) Signed-off-by: Simon Glass <sjg@chromium.org>
Simon Glass [Mon, 13 Nov 2017 04:52:08 +0000 (21:52 -0700)]
binman: Rename tests to ftest
At present these tests use the same filename as patman. This adds
confusion when running all tests, since error messages look very similar.
In fact binman tries to run the wrong tests at present.
Simon Glass [Mon, 13 Nov 2017 04:52:07 +0000 (21:52 -0700)]
binman: Add a Makefile for test-program compilation
These test programs are includedd as binary files in U-Boot to avoid
having to build them (and associated toolchain differences). Instructions
on building are in the files themselves, but it seems better to provide
a Makefile which can be manually run when desired.
Add a Makefile, separate from the normal build system, to handle this.
Simon Glass [Mon, 13 Nov 2017 04:52:05 +0000 (21:52 -0700)]
binman: Add better Makefile debugging
There is a debugging option in the Makefile to allow people to figure out
which u-boot.dtsi files are used in the build. But is it not easy to use
since it only shows files it finds, not those it is looking for. Update it
and update the mention of it to the docs.
A few header files still have a definition of CONFIG_ENV_SIZE, causing
warnings during buildman runs. This removes the duplicate definitions
from evb_px5.h, geekbox.h and rv1108_common.h.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Andy Yan [Wed, 11 Oct 2017 07:01:31 +0000 (15:01 +0800)]
rockchip: check download key before bootup
Enter download mode if the download key pressed.
Signed-off-by: Andy Yan <andy.yan@rock-chips.com> Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
[Converted printfs in boot_mode.c to debug/pr_err:] Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Andy Yan [Wed, 11 Oct 2017 07:00:49 +0000 (15:00 +0800)]
rockchip: add support for enter to bootrom download mode
Rockchip bootrom will enter download mode if it returns from
spl/tpl with a non-zero value and couldn't find a valid image
in the backup partition.
This patch provide a method to instruct the system to back to
bootrom download mode by checking the BROM_DOWNLOAD_FLAG register.
As the bootrom download function relys on some modules such as
interrupts, so we need to back to bootrom as early as possbile
before the tpl/spl code override the interrupt configurations.
Signed-off-by: Andy Yan <andy.yan@rock-chips.com> Reviewed-by: Kever Yang <kever.yang@rock-chips.com> Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Andy Yan [Wed, 11 Oct 2017 07:00:16 +0000 (15:00 +0800)]
rockchip: make boot_mode related codes reused across all platforms
setup_boot_mode function use the same logic but different
mode register address across all the rockchip platforms,
so it's better to make this function reused across all the
platforms, and let the mode register address setting from
the config file.
Signed-off-by: Andy Yan <andy.yan@rock-chips.com> Reviewed-by: Simon Glass <sjg@chromium.org> Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de> Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Kever Yang [Fri, 3 Nov 2017 07:16:13 +0000 (15:16 +0800)]
rockchip: clock: update sysreset driver binding
Using priv for new sysreset driver binding.
Signed-off-by: Kever Yang <kever.yang@rock-chips.com> Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Philipp Tomsich [Tue, 21 Nov 2017 21:28:55 +0000 (22:28 +0100)]
rockchip: sysreset: update Makefile to work with merged sysreset driver
After applying the merged sysreset driver, there are build failures
due to an out-of-sync Makefile. This updates drivers/sysreset/Makefile
to address these build failures.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Kever Yang [Fri, 3 Nov 2017 07:16:12 +0000 (15:16 +0800)]
rockchip: sysreset: merge into one common driver
Use a common driver for all Rockchip SOC instead of one for each SoC.
Use driver_data for reg offset.
Signed-off-by: Kever Yang <kever.yang@rock-chips.com> Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:18 +0000 (16:21 +0200)]
rockchip: mkimage: remove unused code-paths (spl_boot0 is now implied)
With all targets converted to generate prepadded images, this removes
the spl_boot0 field from our config structure and removes the unused
code-path (for images that are not prepadded): i.e. spl_boot0 is now
implied as 'true' and the code is specialised by removing the other
case.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:16 +0000 (16:21 +0200)]
rockchip: back-to-bootrom: allow passing a cmd to the bootrom
The BROM supports forcing it to enter download-mode, if an appropriate
result/cmd-word is returned to it. There already is a series to
support this in review, so this prepares the (newly C-version) of the
back-to-bootrom code to accept a cmd to passed on to the BROM.
All the existing call-sites are adjusted to match the changed function
signature.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Tested-by: Andy Yan <andy.yan@rock-chips.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:15 +0000 (16:21 +0200)]
rockchip: rk3188: use boot0 hook to load up SPL in 2 steps
For the RK3188, the BROM will attempt to load up the first stage
image (SPL for the RK3188) in two steps: first 1KB to offset 0x800
in the SRAM and then the remainder to offset 0xc00 in the SRAM.
It always enters at 0x804, though.
With this changeset, the RK3188 boot removes the TPL (stub) stage and
builds a single SPL binary that utilizes the early back-to-bootrom via
the boot0-hook.
Consequently, the passing of the saved boot params via pmu->os_reg[2]
is also removed.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:14 +0000 (16:21 +0200)]
rockchip: back-to-bootrom: replace assembly-implementation with C-code
The back-to-bootrom implementation for Rockchip has always relied on
the stack-pointer being valid on entry, so there was little reason to
have this as an assembly implementation.
This provides a new C-only implementation of save_boot_params and
back_to_bootrom (relying on setjmp/longjmp) and removes the older
assembly-only implementation.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Tested-by: Andy Yan <andy.yan@rock-chips.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:13 +0000 (16:21 +0200)]
arm: provide a PCS-compliant setjmp implementation
The previous setjmp-implementation (as a static inline function that
contained an 'asm volatile' sequence) was extremely fragile: (some
versions of) GCC optimised the set of registers. One critical example
was the removal of 'r9' from the clobber list, if -ffixed-reg9 was
supplied.
To increase robustness and ensure PCS-compliant behaviour, the setjmp
and longjmp implementation are now in assembly and closely match what
one would expect to find in a libc implementation.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Tested-by: Andy Yan <andy.yan@rock-chips.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:12 +0000 (16:21 +0200)]
arm: mark save_boot_params_ret as a function
As no '.type' was set for save_boot_params_ret in start.S, binutils
did not track whether it was emitted as A32 or T32. By properly
marking save_boot_params_ret as a potential function entry, we can
make sure that the compiler will insert the appropriate instructions
for branching to save_boot_params_ret both for call-sites emitted as
A32 and T32.
Reported-by: Andy Yan <andy.yan@rock-chips.com> Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Tested-by: Andy Yan <andy.yan@rock-chips.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:11 +0000 (16:21 +0200)]
arm: make save_boot_params_ret prototype visible for AArch64
The save_boot_params_ret() prototype (for those of us, that have a
valid SP on entry and can implement save_boot_params() in C), was
previously only defined for !defined(CONFIG_ARM64).
This moves the declaration to a common block to ensure the prototype
is available to everyone that might need it.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Tested-by: Andy Yan <andy.yan@rock-chips.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:10 +0000 (16:21 +0200)]
rockchip: boot0 hook: support early return for RK3188/RK3066-style BROM
Some Rockchip BROM versions (e.g. the RK3188 and RK3066) first read 1KB data
from NAND into SRAM and executes it. Then, following a return to bootrom, the
BROM loads additional code to SRAM (not overwriting the first block read) and
reenters at the same address as the first time.
To support booting either a TPL (on the RK3066) or SPL (on the RK3188) using
this model of having to count entries, this commit adds code to the boot0
hook to track the number of entries and handle them accordingly.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com> Signed-off-by: Paweł Jarosz <paweljarosz3691@gmail.com> Tested-by: Andy Yan <andy.yan@rock-chips.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:09 +0000 (16:21 +0200)]
bcm281xx: boot0 hook: adjust to unified boot0 semantics
This updates the BCM281xx boot0-hook to the updated boot0 semantics
by emitting _start and the vector table before the boot0 hook (as
was the case before).
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:08 +0000 (16:21 +0200)]
bcm235xx: boot0 hook: adjust to unified boot0 semantics
This updates the BCM235xx boot0-hook to the updated boot0 semantics
by emitting _start and the vector table before the boot0 hook (as
was the case before).
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Version-changes: 5
- ran 'whitespace-cleanup'
Philipp Tomsich [Tue, 10 Oct 2017 14:21:07 +0000 (16:21 +0200)]
socfpga: boot0 hook: adjust to unified boot0 semantics
With the updated boot0 semantics (i.e. giving the boot0-hook control
over when and where the vector table is emitted), the boot0-hook for
the socfpga needs to be adjusted.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Kever Yang [Tue, 10 Oct 2017 14:21:05 +0000 (16:21 +0200)]
rockchip: rk3288: use aligned address for SPL_TEXT_BASE
After we use boot0 hook, we can use offset '000' instead of '004' as
SPL_TEXT_BASE.
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
[Updated tag in commit summary:] Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Kever Yang [Tue, 10 Oct 2017 14:21:04 +0000 (16:21 +0200)]
rockchip: mkimage: use spl_boot0 for all Rockchip SoCs
Enable the spl_boot0 in SPL and use the pre-padding TAG memory,
the mkimage do not need to pad it but only need to replace the value
with correct TAG value.
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
[Updated:] Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:03 +0000 (16:21 +0200)]
rockchip: enable boot0-hook for all Rockchip SoCs
Rockchip SoCs bootrom design is like this:
- First 2KB or 4KB internal memory is for bootrom stack and heap;
- Then the first 4-byte suppose to be a TAG like 'RK33';
- The the following memory address end with '0004' is the first
instruction load and running by bootrom;
Let's use the boot0 hook to reserve the first 4-byte tag for all
the Rockchip SoCs.
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
[Commit message taken from an older patch by:] Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Kever Yang [Tue, 10 Oct 2017 14:21:02 +0000 (16:21 +0200)]
rockchip: boot0: align to 0x20 for armv7 '_start'
The '_start' is using as vector table base address, and will write
to VBAR register, so it needs to be aligned to 0x20 for armv7.
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
[Updated to current code base:] Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Philipp Tomsich [Tue, 10 Oct 2017 14:21:01 +0000 (16:21 +0200)]
arm: boot0 hook: move boot0 hook before '_start'
The boot0 hook on ARM does not insert its payload before the vector
table. This is both a mismatch with thec comment above it and
contradict usage of the boot0 hook on ARM64.
To fix this (and unify the semantics for ARM and ARM64), we change the
boot0-hook semantics on ARM to match those on ARM64:
(1) if a boot0-hook is present it is inserted at the start of
the image
(2) if a boot0-hook is present, emitting the ARM vector table
(and the _start) symbol are suppressed in vectors.S and
the boot0-hook has full control over where and when it
wants to emit these
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Faiz Abbas [Tue, 14 Nov 2017 10:42:31 +0000 (16:12 +0530)]
thermal: ti-bandgap: Add support for temperature sensor
The dra7xx series of SOCs contain a temperature sensor and an
associated analog-to-digital converter (ADC) which produces
an output which is proportional to the SOC temperature.
Add support for this temperature sensor.
Signed-off-by: Faiz Abbas <faiz_abbas@ti.com> Reviewed-by: Simon Glass <sjg@chromium.org>
Stefan Agner [Tue, 14 Nov 2017 14:47:18 +0000 (15:47 +0100)]
envtools: make sure version/timestamp header file are available
With commit 84d46e7e8948 ("tools: env: allow to print U-Boot version")
the fw_env utilities need the version.h header file. Building only
the envtools in a pristine build directory will fail due to missing
header files.
Make sure the header files are a dependency of the envtools target.
Fixes: 84d46e7e8948 ("tools: env: allow to print U-Boot version") Signed-off-by: Stefan Agner <stefan.agner@toradex.com> Tested-by: Peter Robinson <pbrobinson@gmail.com> Reviewed-by: Simon Glass <sjg@chromium.org>
When building on a multi-core machine for an SPL-enabled board that
also uses CONFIG_OF_EMBED, the following error can be encountered
due to a race condition:
make[3]: *** No rule to make target 'spl/dts/dt.dtb.o', needed by
'spl/dts/built-in.o'. Stop.
../scripts/Makefile.spl:364: recipe for target 'spl/dts' failed
make[2]: *** [spl/dts] Error 2
make[2]: *** Waiting for unfinished jobs....
A reliable way to trigger this race condition is to add "sleep 60" to
the end of the "arch-dtbs" rule's recipe in "dts/Makefile" and to build
U-Boot against a board which uses the CONFIG_OF_EMBED and CONFIG_SPL
options using "make -j8" or a similar command.
This commit corrects this race condition via the use of CONFIG_OF_EMBED
in the same way that commit 3c00a2c8b5e2 ("Makefile: Correct dependency
race condition with TPL") and commit 054b3a1e80fc ("dm: Makefile: Build
of-platdata before SPL") use CONFIG_OF_SEPARATE.
Signed-off-by: M. Vefa Bicakci <m.v.b@runbox.com> Reviewed-by: Simon Glass <sjg@chromium.org>
Tom Rini [Mon, 6 Nov 2017 23:15:11 +0000 (18:15 -0500)]
Kconfig: Introduce USE_BOOTCOMMAND and migrate BOOTCOMMAND
We first introduce CONFIG_USE_BOOTCOMMAND, similar to
CONFIG_USE_BOOTARGS. We then migrate CONFIG_BOOTCOMMAND for most
CONFIG_DISTRO_DEFAULT users. In some cases platforms have a complex
scheme around this usage, and these have been defered for the moment so
that platform maintainers can work on a migration plan.
Signed-off-by: Tom Rini <trini@konsulko.com> Reviewed-by: Lukasz Majewski <lukma@denx.de>
Dongjin Kim [Sat, 28 Oct 2017 04:22:27 +0000 (00:22 -0400)]
arm: config: fix default console only to specify the device
Since CONFIG_DEFAULT_CONSOLE is already started with "console=",
the console argument in CONFIG_EXTRA_ENV_SETTINGS is expanded to
"console=console=ttySAC1,115200n8" and this causes the wrong
console device.
Minghuan Lian [Fri, 20 Oct 2017 02:45:50 +0000 (10:45 +0800)]
dm: pci: change bus number register setting compliant with Linux
This patch is to change U-Boot PCI bus assignement compliant with Linux.
It means each PCIe controller's bus number is 0, not the current maximum
PCI bus number, when start to scan this controller.
Signed-off-by: Minghuan Lian <Minghuan.Lian@nxp.com> Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com> Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
André Draszik [Tue, 3 Oct 2017 15:55:53 +0000 (16:55 +0100)]
tpm: add more useful NV storage permission flags
TPM_NV_PER_PPREAD: physical presence needed for reading
TPM_NV_PER_WRITEDEFINE: persistent write lock by writing size 0
TPM_NV_PER_WRITEALL: write in one go
Signed-off-by: André Draszik <adraszik@tycoint.com> Acked-by: Simon Glass <sjg@chromium.org>
André Draszik [Tue, 3 Oct 2017 15:55:52 +0000 (16:55 +0100)]
tpm: add tpm_get_random()
Add a function to obtain random data from the TPM.
Signed-off-by: André Draszik <adraszik@tycoint.com>
Added commit message, add cast to min() Signed-off-by: Simon Glass <sjg@chromium.org> Acked-by: Simon Glass <sjg@chromium.org>
Wilson Lee [Fri, 3 Nov 2017 06:39:51 +0000 (23:39 -0700)]
serial: nulldev: Implement "pending" function to fix tstc return "true"
In U-boot, serial_tstc was use to determine is there have a character in
serial console that pending for read. If there is no "pending" function
implemented in serial driver, the serial-uclass will return "true(1)"
to indicate there have a character pending to read.
Thus, read a character from nulldev serial will result in continuous
getting -EAGAIN return which might lead system to hang.
This commit is to fix a bug in nulldev serial which implement "pending"
function in nulldev serial to always indicate there is no character in
console that pending for read.
Signed-off-by: Wilson Lee <wilson.lee@ni.com> Cc: Joe Hershberger <joe.hershberger@ni.com> Cc: Keng Soon Cheah <keng.soon.cheah@ni.com> Cc: Chen Yee Chew <chen.yee.chew@ni.com> Cc: Bin Meng <bmeng.cn@gmail.com>