ARM: bcm2835: implement phys_to_bus/bus_to_phys

The BCM283[56] contain both a L1 and L2 cache between the GPU (a/k/a
VideoCore CPU?) and DRAM. DMA-capable peripherals can also optionally
access DRAM via this same  L2 cache (although they always bypass the L1
cache). Peripherals select whether to use or bypass the cache via the
top two bits of the bus address.

An IOMMU exists between the ARM CPU and the rest of the system. This
controls whether the ARM CPU's accesses use or bypass the L1 and/or L2
cache. This IOMMU is configured/controlled exclusively by the VideoCore
CPU.

In order for DRAM accesses made by the ARM core to be coherent with
accesses made by other DMA peripherals, we must program a bus address
into those peripherals that causes the peripheral's accesses to use the
same set of caches that the ARM core's accesses will use.

On the RPi1, the VideoCore firmware sets up the IOMMU to enable use of
the L2 cache. This corresponds to addresses based at 0x40000000.

On the RPi2, the VideoCore firmware sets up the IOMMU to disable use of
the L2 cache. This corresponds to addresses based at 0xc0000000.

This patch implements U-Boot's phys_to_bus/bus_to_phys APIs according
to those rules.

For full details of this setup, please see Dom Cobley's description at:
http://lists.denx.de/pipermail/u-boot/2015-March/208201.html
http://permalink.gmane.org/gmane.comp.boot-loaders.u-boot/215038
https://www.mail-archive.com/u-boot@lists.denx.de/msg166568.html

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>

diff --git a/arch/arm/mach-bcm283x/Kconfig b/arch/arm/mach-bcm283x/Kconfig
index b43f2d91fd01419153a10e0b016cb27e082572e4..0c04c301b23f0ff8816af32f15086127d18114f8 100644 (file)
--- a/arch/arm/mach-bcm283x/Kconfig
+++ b/arch/arm/mach-bcm283x/Kconfig
@@ -23,6 +23,9 @@ config DM_SERIAL
 config DM_GPIO
        default y
 
+config PHYS_TO_BUS
+       default y
+
 config SYS_BOARD
        default "rpi" if TARGET_RPI
        default "rpi_2" if TARGET_RPI_2

diff --git a/arch/arm/mach-bcm283x/Makefile b/arch/arm/mach-bcm283x/Makefile
index 2505428bab41735607764b75dae47951208b6fdf..ac27d00e2a087001960116e5f66f76693361a567 100644 (file)
--- a/arch/arm/mach-bcm283x/Makefile
+++ b/arch/arm/mach-bcm283x/Makefile
@@ -5,4 +5,4 @@
 #
 
 obj-$(CONFIG_TARGET_RPI) += lowlevel_init.o
-obj-y  += init.o reset.o timer.o mbox.o
+obj-y  += init.o reset.o timer.o mbox.o phys2bus.o

diff --git a/arch/arm/mach-bcm283x/phys2bus.c b/arch/arm/mach-bcm283x/phys2bus.c
new file mode 100644 (file)
index 0000000..fc1c299
--- /dev/null
+++ b/arch/arm/mach-bcm283x/phys2bus.c
@@ -0,0 +1,22 @@
+/*
+ * Copyright 2015 Stephen Warren
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#include <config.h>
+#include <phys2bus.h>
+
+unsigned long phys_to_bus(unsigned long phys)
+{
+#ifdef CONFIG_BCM2836
+       return 0xc0000000 | phys;
+#else
+       return 0x40000000 | phys;
+#endif
+}
+
+unsigned long bus_to_phys(unsigned long bus)
+{
+       return bus & ~0xc0000000;
+}