From 4489750fa56e5c2ed49b3bf3590c0bfdab1a8a08 Mon Sep 17 00:00:00 2001 From: Doug Anderson Date: Mon, 11 May 2015 12:44:28 -0700 Subject: [PATCH] i2c: rk3x: Increase wait timeout to 1 second MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Although unlikely, it is remotely possible for an i2c command to need more than 200ms complete. Unlike smbus, i2c devices can clock stretch for an unspecified amount of time. The longest time I've seen specified for a device is 144ms (bq27541 battery gas), but one could imagine a device taking a bit slower. 1 second "ought to be enough for anyone." The above is not the only justifcation for going above 200ms for a timeout, though. It turns out that if you've got a large number of printks going out to a serial console, interrupts on a CPU can be disabled for hundreds of milliseconds. That's not a great situation to be in to start with (maybe we should put a cap in vprintk_emit()) but it's pretty annoying to start seeing unexplained i2c timeouts. Note that to understand why we can timeout when printk has interrupts disabled, you need to understand that on current Linux ARM kernels interrupts are routed to a single CPU in a multicore system. Thus, you can get: 1. CPU1 is running rk3x_i2c_xfer() 2. CPU0 calls vprintk_emit(), which disables all IRQs on CPU0. 3. I2C interrupt is ready but is set to only run on CPU0, where IRQs are disabled. 4. CPU1 timeout expires. I2C interrupt is still ready, but CPU0 is still sitting in the same vprintk_emit() 5. CPU1 sees that no interrupt happened in 200ms, so timeout. A normal system shouldn't see i2c timeouts anyway, so increasing the timeout should help people debugging without hurting other people excessively. Signed-off-by: Doug Anderson Tested-by: Caesar Wang Acked-by: Uwe Kleine-König Signed-off-by: Wolfram Sang --- drivers/i2c/busses/i2c-rk3x.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c index 019d5426fe52..72e97e306bd9 100644 --- a/drivers/i2c/busses/i2c-rk3x.c +++ b/drivers/i2c/busses/i2c-rk3x.c @@ -72,7 +72,7 @@ enum { #define REG_INT_ALL 0x7f /* Constants */ -#define WAIT_TIMEOUT 200 /* ms */ +#define WAIT_TIMEOUT 1000 /* ms */ #define DEFAULT_SCL_RATE (100 * 1000) /* Hz */ enum rk3x_i2c_state {