[PATCH 04/15] drm/amd/display: Replace msleep with udelay while read edid return defer.

[Christian König]

No idea what that is. I can include delay.h just fine in the rest of the 
driver.

Must be something DC specific.

Regards,
Christian.

Am 17.09.20 um 16:39 schrieb Zhang, Jinlong:
> HI Christian
> While #include <linux/delay.h>, it prompt ..\..\..\..\..\dc\dce\dce_aux.c(31): fatal error C1083: Cannot open include file: 'linux/delay.h': No such file or directory
> Could you help to check how to include the header of void usleep_range(unsigned long min, unsigned long max);
>
> -----Original Message-----
> From: Zhuo, Qingqing <Qingqing.Zhuo at amd.com>
> Sent: Thursday, September 17, 2020 9:02 PM
> To: Koenig, Christian <Christian.Koenig at amd.com>; Alex Deucher <alexdeucher at gmail.com>
> Cc: Brol, Eryk <Eryk.Brol at amd.com>; Li, Sun peng (Leo) <Sunpeng.Li at amd.com>; Lakha, Bhawanpreet <Bhawanpreet.Lakha at amd.com>; Siqueira, Rodrigo <Rodrigo.Siqueira at amd.com>; amd-gfx list <amd-gfx at lists.freedesktop.org>; Zhang, Jinlong <Jinlong.Zhang at amd.com>; Wentland, Harry <Harry.Wentland at amd.com>
> Subject: RE: [PATCH 04/15] drm/amd/display: Replace msleep with udelay while read edid return defer.
>
> [AMD Official Use Only - Internal Distribution Only]
>
> Am 17.09.20 um 00:18 schrieb Alex Deucher:
>>> On Wed, Sep 16, 2020 at 6:16 PM Zhuo, Qingqing <Qingqing.Zhuo at amd.com> wrote:
>>>> [AMD Official Use Only - Internal Distribution Only]
>>>>
>>>> On Wed, Sep 16, 2020 at 3:42 PM Qingqing Zhuo <qingqing.zhuo at amd.com> wrote:
>>>>> From: jinlong zhang <jinlong.zhang at amd.com>
>>>>>
>>>>> [why]
>>>>> while read edid return defer, then it enter to msleep, but it
>>>>> actually took more time during msleep, this will cause remaining
>>>>> edid read fail.
>>>>>
>>>>> [how]
>>>>> Replacing msleep with udelay, it will not take any extra time, edid return pass finally.
>>>> How long of a delay are we talking about here?  Some platforms don't support long udelays and someone will send a patch to change this to msleep.
>>>>
>>>> Alex
>>>>
>>>> ---------------------
>>>>
>>>> Hi Alex,
>>>>
>>>> It's between 0-5ms for generic cases, though there exist some dongle workaround cases where we will do 70ms. Would this be a concern?
>>> I think ARM has a limit of 2ms for udelay.
>> Yeah, there is even a define somewhere for this.
>> If you need a delay which is longer than this but still more precise than msleep() then there is the high precision timer sleep as alternative.
>> I've forgotten the function name to use here, but there was a LWN article about this a few years ago. You just need to google a bit.
> Hi Alex and Christian,
>
> Thanks a lot for the input! Given what's been discussed, I will drop this patch for now.
>
> Regards,
> Lillian
>
>> Regards,
>> Christian.
>>> Alex
>>>
>>>> Thank you,
>>>> Lillian
>>>>
>>>>
>>>>> Signed-off-by: jinlong zhang <jinlong.zhang at amd.com>
>>>>> Reviewed-by: Wenjing Liu <Wenjing.Liu at amd.com>
>>>>> Acked-by: Qingqing Zhuo <qingqing.zhuo at amd.com>
>>>>> ---
>>>>> drivers/gpu/drm/amd/display/dc/dce/dce_aux.c | 2 +-
>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_aux.c
>>>>> b/drivers/gpu/drm/amd/display/dc/dce/dce_aux.c
>>>>> index 743042d5905a..cdcad82765e0 100644
>>>>> --- a/drivers/gpu/drm/amd/display/dc/dce/dce_aux.c
>>>>> +++ b/drivers/gpu/drm/amd/display/dc/dce/dce_aux.c
>>>>> @@ -653,7 +653,7 @@ bool dce_aux_transfer_with_retries(struct ddc_service *ddc,
>>>>>                                           if ((*payload->reply == AUX_TRANSACTION_REPLY_AUX_DEFER) ||
>>>>>                                                   (*payload->reply == AUX_TRANSACTION_REPLY_I2C_OVER_AUX_DEFER)) {
>>>>>                                                   if (payload->defer_delay > 0)
>>>>> -                                                       msleep(payload->defer_delay);
>>>>> +
>>>>> + udelay(payload->defer_delay * 1000);
>>>>>                                           }
>>>>>                                   }
>>>>>                                   break;
>>>>> --
>>>>> 2.17.1
>>>>>
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