[Intel-gfx] [PATCH] drm/i915: Retry few time if gpiod_get fails during intel_dsi_init

[Daniel Vetter]

On Wed, Jan 20, 2016 at 02:08:06PM +0530, Kumar, Shobhit wrote:
> 
> On 01/20/2016 01:50 AM, Daniel Vetter wrote:
> >On Tue, Jan 19, 2016 at 09:00:40PM +0530, Kumar, Shobhit wrote:
> >>On 01/19/2016 08:45 PM, Shobhit Kumar wrote:
> >>>INTEL_SOC_PMIC is loading later than I915 failing the gpiod_get and
> >>>pwm_get calls in i915. Add a retry to give time for the INTEL_SOC_PMIC
> >>>to load. This was fine till now but broke in latest kernel. Maybe load
> >>>time for the INTEL_SOC_PMIC has increased.
> >>>
> >>>Since the lookup tables for GPIO (panel enable) and PWM both are
> >>>exported by same intel_soc_pmic driver, just retrying for the driver to
> >>>load in intel_dsi_init is sufficient. By the time we come to
> >>>setup_backlight, pwm would have been exported as well.
> >>
> >>Maybe we should play with initcalls here but I was not sure how it will
> >>impact if I change it for PMIC driver. IIRC, this discussion came up from
> >>Daniel at the time of original patches also but somehow did not close
> >>decidedly and has come back as a regression.
> >
> >The correct way to handle this is to bail out with -EPROBE_DEFER. This is
> >how this is meant to be, no amount of random retrying will fix this
> >properly for such dynamic inter-module depencies.
> 
> Yeah, you are right, retries are working pretty randomly. I made a quick
> changes all the way up to i915_driver_load returning -EPROBE_DEFER form
> intel_setup_outputs and it seems to work.
> 
> >
> >And yes this is going to be a world-class test for our module load unwind
> >code.
> 
> Well it seems to be working :) Will have a cleaned up patch for review. Also
> need to take care of this in the LPSS_PWM patches as well.

You're extremely lucky then I'd say. Let's see whether CI agrees and then
merge this ;-)

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch