linux-kernel - Re: [PATCH 3/7] drm/msm/dp: reset aux controller after dp_aux_cmd_fifo

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Date:   Thu, 08 Jul 2021 14:59:53 -0700
From:   khsieh@...eaurora.org
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run, abhinavk@...eaurora.org, aravindh@...eaurora.org,
        airlied@...ux.ie, daniel@...ll.ch, bjorn.andersson@...aro.org,
        linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] drm/msm/dp: reset aux controller after
 dp_aux_cmd_fifo_tx() failed.

On 2021-07-08 00:34, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2021-07-06 10:20:16)
>> Aux hardware calibration sequence requires resetting the aux 
>> controller
>> in order for the new setting to take effect. However resetting the AUX
>> controller will also clear HPD interrupt status which may accidentally
>> cause pending unplug interrupt to get lost. Therefore reset aux
>> controller only when link is in connection state when 
>> dp_aux_cmd_fifo_tx()
>> fail. This fixes Link Layer CTS cases 4.2.1.1 and 4.2.1.2.
>> 
>> Signed-off-by: Kuogee Hsieh <khsieh@...eaurora.org>
>> ---
>>  drivers/gpu/drm/msm/dp/dp_aux.c | 3 +++
>>  1 file changed, 3 insertions(+)
>> 
>> diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c 
>> b/drivers/gpu/drm/msm/dp/dp_aux.c
>> index 4a3293b..eb40d84 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_aux.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_aux.c
>> @@ -353,6 +353,9 @@ static ssize_t dp_aux_transfer(struct drm_dp_aux 
>> *dp_aux,
>>                         if (!(aux->retry_cnt % MAX_AUX_RETRIES))
>>                                 
>> dp_catalog_aux_update_cfg(aux->catalog);
>>                 }
>> +               /* reset aux if link is in connected state */
>> +               if (dp_catalog_link_is_connected(aux->catalog))
> 
> How do we avoid resetting aux when hpd is unplugged and then plugged
> back in during an aux transfer?
i am not sure this is possible.
it should get unplug interrupt followed by plugin interrupt.
In this case, aux will be re set and initialized
> 
>> +                       dp_catalog_aux_reset(aux->catalog);
>>         } else {
>>                 aux->retry_cnt = 0;
>>                 switch (aux->aux_error_num) {
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
>> Forum,
>> a Linux Foundation Collaborative Project
>>