linux-kernel - Re: [PATCH 1/1] drm/panel: truly: Add additional delay after pulling down reset gpio

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Date:   Wed, 29 May 2019 11:27:10 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Marc Gonzalez <marc.w.gonzalez@...e.fr>, airlied@...ux.ie,
        thierry.reding@...il.com, daniel@...ll.ch
Cc:     Rob Clark <robdclark@...il.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        MSM <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] drm/panel: truly: Add additional delay after pulling
 down reset gpio



On 5/28/2019 2:13 PM, Marc Gonzalez wrote:
> On 27/05/2019 12:26, Vivek Gautam wrote:
>
>> MTP SDM845 panel seems to need additional delay to bring panel
>> to a workable state. Running modetest without this change displays
>> blurry artifacts.
>>
>> Signed-off-by: Vivek Gautam <vivek.gautam@...eaurora.org>
>> ---
>>   drivers/gpu/drm/panel/panel-truly-nt35597.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/gpu/drm/panel/panel-truly-nt35597.c b/drivers/gpu/drm/panel/panel-truly-nt35597.c
>> index fc2a66c53db4..aa7153fd3be4 100644
>> --- a/drivers/gpu/drm/panel/panel-truly-nt35597.c
>> +++ b/drivers/gpu/drm/panel/panel-truly-nt35597.c
>> @@ -280,6 +280,7 @@ static int truly_35597_power_on(struct truly_nt35597 *ctx)
>>   	gpiod_set_value(ctx->reset_gpio, 1);
>>   	usleep_range(10000, 20000);
>>   	gpiod_set_value(ctx->reset_gpio, 0);
>> +	usleep_range(10000, 20000);
> I'm not sure usleep_range() makes sense with these values.
>
> AFAIU, usleep_range() is typically used for sub-jiffy sleeps, and is based
> on HRT to generate an interrupt.
>
> Once we get into jiffy granularity, it seems to me msleep() is good enough.
> IIUC, it would piggy-back on the jiffy timer interrupt.
>
> In short, why not just use msleep(10); ?

I am just maintaining the symmetry across older code.

Thanks
Vivek
>
> Regards.