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

[Kuogee Hsieh <quic_khsieh@quicinc.com>]

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.

>
>>
>> Changes in v5:
>> -- split into two patches
>>
>> Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.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;
>>   }
>