[7/7] drm/msm/dp: retrain link when loss of symbol lock detected

Main link symbol locked is achieved at end of link training 2. Some
dongle main link symbol may become unlocked again if host did not end
link training soon enough after completion of link training 2. Host
have to re train main link if loss of symbol lock detected before
end link training so that the coming video stream can be transmitted
to sink properly.

Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
---
 drivers/gpu/drm/msm/dp/dp_ctrl.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

Quoting Kuogee Hsieh (2021-07-06 10:20:20)
> Main link symbol locked is achieved at end of link training 2. Some
> dongle main link symbol may become unlocked again if host did not end
> link training soon enough after completion of link training 2. Host
> have to re train main link if loss of symbol lock detected before
> end link training so that the coming video stream can be transmitted
> to sink properly.
>
> Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>

I guess this is a fix for the original driver, so it should be tagged
with Fixes appropriately.

> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index 0cb01a9..e616ab2 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1661,6 +1661,25 @@ static bool dp_ctrl_any_lane_cr_lose(struct dp_ctrl_private *ctrl,
>         return false;
>  }
>
> +static bool dp_ctrl_loss_symbol_lock(struct dp_ctrl_private *ctrl)
> +{
> +       u8 link_status[6];

Can we use link_status[DP_LINK_STATUS_SIZE] instead?

> +       u8 status;
> +       int i;
> +       int lane = ctrl->link->link_params.num_lanes;

s/lane/num_lanes/

would make the code easier to read

> +
> +       dp_ctrl_read_link_status(ctrl, link_status);
> +
> +       for (i = 0; i < lane; i++) {
> +               status = link_status[i / 2];
> +               status >>= ((i % 2) * 4);
> +               if (!(status & DP_LANE_SYMBOL_LOCKED))
> +                       return true;
> +       }
> +
> +       return false;
> +}
> +
>  int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
>  {
>         int rc = 0;
> @@ -1777,6 +1796,17 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
>         return rc;
>  }
>
> +static int dp_ctrl_link_retrain(struct dp_ctrl_private *ctrl)
> +{
> +       int ret = 0;

Please drop init of ret.

> +       u8 cr_status[2];
> +       int training_step = DP_TRAINING_NONE;
> +
> +       ret = dp_ctrl_setup_main_link(ctrl, cr_status, &training_step);

as it is assigned here.

> +
> +       return ret;

And indeed, it could be 'return dp_ctrl_setup_main_link()' instead.

> +}
> +
>  int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>  {
>         int ret = 0;
> @@ -1802,6 +1832,10 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>                 }
>         }
>
> +       /* if loss symbol lock happen, then retaining the link */

retain or retrain? The comment seems to be saying what the code says "if
loss retrain", so the comment is not very useful.

> +       if (dp_ctrl_loss_symbol_lock(ctrl))
> +               dp_ctrl_link_retrain(ctrl);
> +
>         /* stop txing train pattern to end link training */
>         dp_ctrl_clear_training_pattern(ctrl);
>

On 2021-07-08 00:21, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2021-07-06 10:20:20)
>> Main link symbol locked is achieved at end of link training 2. Some
>> dongle main link symbol may become unlocked again if host did not end
>> link training soon enough after completion of link training 2. Host
>> have to re train main link if loss of symbol lock detected before
>> end link training so that the coming video stream can be transmitted
>> to sink properly.
>> 
>> Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
> 
> I guess this is a fix for the original driver, so it should be tagged
> with Fixes appropriately.
Actually, this is fix on patch #6 : drm/msm/dp: do not end dp link 
training until video is ready
Should i merge patch #6 and #7 together?
Or can you suggest what should I do?
> 
>> ---
>>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 34 
>> ++++++++++++++++++++++++++++++++++
>>  1 file changed, 34 insertions(+)
>> 
>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c 
>> b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> index 0cb01a9..e616ab2 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> @@ -1661,6 +1661,25 @@ static bool dp_ctrl_any_lane_cr_lose(struct 
>> dp_ctrl_private *ctrl,
>>         return false;
>>  }
>> 
>> +static bool dp_ctrl_loss_symbol_lock(struct dp_ctrl_private *ctrl)
>> +{
>> +       u8 link_status[6];
> 
> Can we use link_status[DP_LINK_STATUS_SIZE] instead?
> 
>> +       u8 status;
>> +       int i;
>> +       int lane = ctrl->link->link_params.num_lanes;
> 
> s/lane/num_lanes/
> 
> would make the code easier to read
> 
>> +
>> +       dp_ctrl_read_link_status(ctrl, link_status);
>> +
>> +       for (i = 0; i < lane; i++) {
>> +               status = link_status[i / 2];
>> +               status >>= ((i % 2) * 4);
>> +               if (!(status & DP_LANE_SYMBOL_LOCKED))
>> +                       return true;
>> +       }
>> +
>> +       return false;
>> +}
>> +
>>  int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
>>  {
>>         int rc = 0;
>> @@ -1777,6 +1796,17 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
>>         return rc;
>>  }
>> 
>> +static int dp_ctrl_link_retrain(struct dp_ctrl_private *ctrl)
>> +{
>> +       int ret = 0;
> 
> Please drop init of ret.
> 
>> +       u8 cr_status[2];
>> +       int training_step = DP_TRAINING_NONE;
>> +
>> +       ret = dp_ctrl_setup_main_link(ctrl, cr_status, 
>> &training_step);
> 
> as it is assigned here.
> 
>> +
>> +       return ret;
> 
> And indeed, it could be 'return dp_ctrl_setup_main_link()' instead.
> 
>> +}
>> +
>>  int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>>  {
>>         int ret = 0;
>> @@ -1802,6 +1832,10 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>>                 }
>>         }
>> 
>> +       /* if loss symbol lock happen, then retaining the link */
> 
> retain or retrain? The comment seems to be saying what the code says 
> "if
> loss retrain", so the comment is not very useful.
> 
>> +       if (dp_ctrl_loss_symbol_lock(ctrl))
>> +               dp_ctrl_link_retrain(ctrl);
>> +
>>         /* stop txing train pattern to end link training */
>>         dp_ctrl_clear_training_pattern(ctrl);
>>