RE: [PATCH] i2c: nvidia-gpu: Handle timeout correctly in gpu_i2c_check_status()

[Ajay Gupta <ajayg@nvidia.com>]

Kai-Heng

> -----Original Message-----
> From: Kai-Heng Feng <kai.heng.feng@canonical.com>
> Sent: Sunday, March 22, 2020 10:38 PM
> To: Ajay Gupta <ajayg@nvidia.com>
> Cc: Wolfram Sang <wsa@the-dreams.de>; Andy Shevchenko
> <andriy.shevchenko@linux.intel.com>; open list:I2C CONTROLLER DRIVER FOR
> NVIDIA GPU <linux-i2c@vger.kernel.org>; open list <linux-
> kernel@vger.kernel.org>
> Subject: Re: [PATCH] i2c: nvidia-gpu: Handle timeout correctly in
> gpu_i2c_check_status()
> 
> External email: Use caution opening links or attachments
> 
> 
> > On Mar 12, 2020, at 00:58, Kai-Heng Feng <kai.heng.feng@canonical.com>
> wrote:
> >
> > Nvidia card may come with a "phantom" UCSI device, and its driver gets
> > stuck in probe routine, prevents any system PM operations like suspend.
> >
> > Let's handle the unaccounted case that the target time equals to
> > jiffies in gpu_i2c_check_status(), so the UCSI driver can let the
> > probe fail as it should.
If status is not seen in 999.5 ms then I don't see any reason why it will come
exactly at 1000ms. In fact,  we expect status to be seen within 160ms as per
I2C_MST_I2C0_TIMING_TIMEOUT_CLK_CNT (16 cycle) and 
I2C_MST_I2C0_TIMING_SCL_PERIOD_100KHZ (10ms/cycle) programmed in 
I2C_MST_I2C0_TIMING Register. We already have enough extra time to look
For response.

Thanks
> nvpublic
> >
> > Fixes: c71bcdcb42a7 ("i2c: add i2c bus driver for NVIDIA GPU")
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> 
> A gentle ping...
> 
> > ---
> > drivers/i2c/busses/i2c-nvidia-gpu.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-nvidia-gpu.c
> > b/drivers/i2c/busses/i2c-nvidia-gpu.c
> > index 62e18b4db0ed..1988e93c7925 100644
> > --- a/drivers/i2c/busses/i2c-nvidia-gpu.c
> > +++ b/drivers/i2c/busses/i2c-nvidia-gpu.c
> > @@ -88,7 +88,7 @@ static int gpu_i2c_check_status(struct gpu_i2c_dev
> *i2cd)
> >               usleep_range(500, 600);
> >       } while (time_is_after_jiffies(target));
> >
> > -     if (time_is_before_jiffies(target)) {
> > +     if (time_is_before_eq_jiffies(target)) {
> >               dev_err(i2cd->dev, "i2c timeout error %x\n", val);
> >               return -ETIMEDOUT;
> >       }
> > --
> > 2.17.1
> >