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

[Daniel Vetter]

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.

And yes this is going to be a world-class test for our module load unwind
code.
-Daniel

> Regards
> Shobhit
> 
> >
> >Signed-off-by: Shobhit Kumar <shobhit.kumar at intel.com>
> >---
> >  drivers/gpu/drm/i915/intel_dsi.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> >diff --git a/drivers/gpu/drm/i915/intel_dsi.c b/drivers/gpu/drm/i915/intel_dsi.c
> >index 91cef35..e309ef6 100644
> >--- a/drivers/gpu/drm/i915/intel_dsi.c
> >+++ b/drivers/gpu/drm/i915/intel_dsi.c
> >@@ -1192,10 +1192,14 @@ void intel_dsi_init(struct drm_device *dev)
> >  	 * Panel control.
> >  	 */
> >  	if (dev_priv->vbt.dsi.config->pwm_blc == PPS_BLC_PMIC) {
> >+		int retry = 4;
> >+		do {
> >  		intel_dsi->gpio_panel =
> >  			gpiod_get(dev->dev, "panel", GPIOD_OUT_HIGH);
> >+			msleep(50);
> >+		} while (IS_ERR(intel_dsi->gpio_panel) && --retry);
> >
> >-		if (IS_ERR(intel_dsi->gpio_panel)) {
> >+		if (!retry) {
> >  			DRM_ERROR("Failed to own gpio for panel control\n");
> >  			intel_dsi->gpio_panel = NULL;
> >  		}
> >
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch