linux-kernel - Re: [PATCH v5 3/3] drm/msm/dp: retry 3 times if set sink to D0 poweer state failed

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Date:   Wed, 2 Nov 2022 18:51:41 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>,
        dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run, swboyd@...omium.org, dianders@...omium.org,
        vkoul@...nel.org, daniel@...ll.ch, airlied@...ux.ie,
        agross@...nel.org, bjorn.andersson@...aro.org
Cc:     quic_abhinavk@...cinc.com, quic_sbillaka@...cinc.com,
        freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/3] drm/msm/dp: retry 3 times if set sink to D0 poweer
 state failed

On 12/09/2022 22:26, Kuogee Hsieh wrote:
> 
> On 9/12/2022 11:37 AM, Dmitry Baryshkov wrote:
>> On 12/09/2022 19:23, Kuogee Hsieh wrote:
>>> Bring sink out of D3 (power down) mode into D0 (normal operation) mode
>>> by setting DP_SET_POWER_D0 bit to DP_SET_POWER dpcd register. This
>>> patch will retry 3 times if written to DP_SET_POWER register failed.
>>
>> Could you please elaborate this change? Can the sink succeed in 
>> reading the DP_SET_POWER, but fail writing DP_SET_POWER?
> 
> yes, there is possible since it is not only set local sink device but 
> also all downstream sink devices to D0 state.

Ack. Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

> 
>>
>>>
>>> Changes in v5:
>>> -- split into two patches
>>>
>>> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
>>> ---
>>>   drivers/gpu/drm/msm/dp/dp_link.c | 13 ++++++++-----
>>>   1 file changed, 8 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/msm/dp/dp_link.c 
>>> b/drivers/gpu/drm/msm/dp/dp_link.c
>>> index 9d5381d..4360728 100644
>>> --- a/drivers/gpu/drm/msm/dp/dp_link.c
>>> +++ b/drivers/gpu/drm/msm/dp/dp_link.c
>>> @@ -50,6 +50,7 @@ static int dp_aux_link_power_up(struct drm_dp_aux 
>>> *aux,
>>>   {
>>>       u8 value;
>>>       ssize_t len;
>>> +    int i;
>>>         if (link->revision < 0x11)
>>>           return 0;
>>> @@ -61,11 +62,13 @@ static int dp_aux_link_power_up(struct drm_dp_aux 
>>> *aux,
>>>       value &= ~DP_SET_POWER_MASK;
>>>       value |= DP_SET_POWER_D0;
>>>   -    len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
>>> -    if (len < 0)
>>> -        return len;
>>> -
>>> -    usleep_range(1000, 2000);
>>> +    /* retry for 1ms to give the sink time to wake up */
>>> +    for (i = 0; i < 3; i++) {
>>> +        len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
>>> +        usleep_range(1000, 2000);
>>> +        if (len == 1)
>>> +            break;
>>> +    }
>>>         return 0;
>>>   }
>>

-- 
With best wishes
Dmitry