From 124913556c4b99909f40b4bf4ceaefe2b555d6f8 Mon Sep 17 00:00:00 2001 From: Marek Vasut Date: Mon, 4 Nov 2013 14:29:12 +0100 Subject: [PATCH] i2c: mxs_i2c: Squash endless loop The endless waiting for a bit to be set can cause a hang, add a timeout so we prevent such situation. A testcase for such a hang is below. The testcase assumes a device to be present at address 0x50 and a device to NOT be present at address 0x42 . Also note that the "sleep 1" induced delays are imperative for this bug to manifest . i2c read 0x42 0x0.2 0x10 0x42000000 ; sleep 1 ; \ i2c read 0x50 0x0.2 0x10 0x42000000 ; sleep 1 ; \ i2c read 0x42 0x0.2 0x10 0x42000000 The expected result of the above command is: Error reading the chip. Error reading the chip. While without this patch, we observe a hang in the last read from 0x42 precisely when waiting for this bit to be set. Signed-off-by: Marek Vasut Cc: Fabio Estevam Cc: Heiko Schocher Cc: Stefano Babic --- drivers/i2c/mxs_i2c.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/i2c/mxs_i2c.c b/drivers/i2c/mxs_i2c.c index 46106b7712..a298c95e14 100644 --- a/drivers/i2c/mxs_i2c.c +++ b/drivers/i2c/mxs_i2c.c @@ -150,6 +150,7 @@ int i2c_read(uchar chip, uint addr, int alen, uchar *buffer, int len) { struct mxs_i2c_regs *i2c_regs = (struct mxs_i2c_regs *)MXS_I2C0_BASE; uint32_t tmp = 0; + int timeout = MXS_I2C_MAX_TIMEOUT; int ret; int i; @@ -169,9 +170,17 @@ int i2c_read(uchar chip, uint addr, int alen, uchar *buffer, int len) for (i = 0; i < len; i++) { if (!(i & 3)) { - while (readl(&i2c_regs->hw_i2c_queuestat) & - I2C_QUEUESTAT_RD_QUEUE_EMPTY) - ; + while (--timeout) { + tmp = readl(&i2c_regs->hw_i2c_queuestat); + if (!(tmp & I2C_QUEUESTAT_RD_QUEUE_EMPTY)) + break; + } + + if (!timeout) { + debug("MXS I2C: Failed receiving data!\n"); + return -ETIMEDOUT; + } + tmp = readl(&i2c_regs->hw_i2c_queuedata); } buffer[i] = tmp & 0xff; -- 2.39.5