Re: [PATCH] drm/i915: Retry few time if gpiod_get fails during intel_dsi_init

["Kumar, Shobhit" <shobhit.kumar@linux.intel.com>]

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.

Regards
Shobhit
> -Daniel
>
>> Regards
>> Shobhit
>>
>>>
>>> Signed-off-by: Shobhit Kumar <shobhit.kumar@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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>
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