linux-kernel - Re: [PATCH v3 12/14] drm: bridge/analogix_dp: expand the delay time for hpd detect

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Date:	Thu, 20 Aug 2015 03:02:27 -0500
From:	Yakir Yang <ykk@...k-chips.com>
To:	Jingoo Han <jingoohan1@...il.com>
CC:	Heiko Stuebner <heiko@...ech.de>,
	Thierry Reding <treding@...dia.com>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Inki Dae <inki.dae@...sung.com>,
	"joe@...ches.com" <joe@...ches.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	"djkurtz@...gle.com" <djkurtz@...gle.com>,
	"dianders@...gle.com" <dianders@...gle.com>,
	"seanpaul@...gle.com" <seanpaul@...gle.com>,
	Takashi Iwai <tiwai@...e.de>,
	"ajaynumb@...il.com" <ajaynumb@...il.com>,
	Andrzej Hajda <a.hajda@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	David Airlie <airlied@...ux.ie>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	Vincent Palatin <vpalatin@...omium.org>,
	Mark Yao <mark.yao@...k-chips.com>,
	Andy Yan <andy.yan@...k-chips.com>,
	Kumar Gala <galak@...eaurora.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Kishon Vijay Abraham I <kishon@...com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
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	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 12/14] drm: bridge/analogix_dp: expand the delay time
 for hpd detect

Hi Jingoo,

On 08/20/2015 01:11 AM, Jingoo Han wrote:
> On 2015. 8. 19., at PM 11:52, Yakir Yang <ykk@...k-chips.com> wrote:
>> Some edp screen with no hpd signal would need some delay time
>> to ensure that screen would be ready for work, so we can expand
>> the delay time in hpd detect function, it works prefectly on my
>> rk3288 sdk board.
> Then, this delay has a dependency on the "rk3288 sdk" board.
> Also, if the delay time is expanded, the booting time of some Exybos boards will be increased unnecessarily. :-(
>
> So, please add new DT property such as 'hpd-delay' that can be added to board DT files.
>
> If there is not that DT property in DT files, the default value '10' will written to a variable such as 'unsigned int hpd_delay'.
> If there is the DT property in DT files, the delay value will written to the variable when parsing DT values
> and will be used in analogix_dp_detect_hpd().
>
> What I want to say is that there should not be harmful effect on the existing Exynos boards, due to unrelated reasons.

Yeah, you are right, I made an mistake here.

And I want to put this delay to "need-force-hpd" code, cause
this property is for the no-hpd-signal eDP screen.

But strangely, with my this series, I don't need the expand delay
any more, I am not sure which change improved this, I guess
those delay time should come from drm core ?

Whatever seems we don't need this delay for now, and if I can
find the exact reason and realize I still need this delay, I prefer
to add those delay in "need-force-hpd" code.

Thanks,
- Yakir
> Best regards,
> Jingoo Han
>
>> Signed-off-by: Yakir Yang <ykk@...k-chips.com>
>> ---
>> Changes in v3: None
>> Changes in v2: None
>>
>> drivers/gpu/drm/bridge/analogix_dp_core.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix_dp_core.c
>> index 99870f7..75dd44a 100644
>> --- a/drivers/gpu/drm/bridge/analogix_dp_core.c
>> +++ b/drivers/gpu/drm/bridge/analogix_dp_core.c
>> @@ -68,7 +68,7 @@ static int analogix_dp_detect_hpd(struct analogix_dp_device *dp)
>>             return 0;
>>
>>         timeout_loop++;
>> -        usleep_range(10, 11);
>> +        usleep_range(100, 110);
>>     }
>>
>>     /*
>> -- 
>> 1.9.1
>>
>>
>
>


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