[Intel-gfx] [PATCH] drm/i915/dp: Give up link training clock recovery after 10 failed attempts

[Rodrigo Vivi]

On Fri, Jul 13, 2018 at 10:32:15AM -0700, Nathan Ciobanu wrote:
> Limit the link training clock recovery loop to 10 failed attempts at
> LANEx_CR_DONE per DP 1.4 spec.

Where exactly in the spec?

> Some USB-C MST hubs cause us to get
> stuck in this loop on hot-plugging indefinitely as
> drm_dp_clock_recovery_ok() never returns true and none of the
> other conditions occur.

Although it seems really bad situation that we need to avoid...

> 
> Signed-off-by: Nathan Ciobanu <nathan.d.ciobanu at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp_link_training.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> index 4da6e33c7fa1..66c1a70343ba 100644
> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> @@ -129,7 +129,7 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
>  intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
>  {
>  	uint8_t voltage;
> -	int voltage_tries, max_vswing_tries;
> +	int voltage_tries, max_vswing_tries, cr_tries;
>  	uint8_t link_config[2];
>  	uint8_t link_bw, rate_select;
>  
> @@ -172,6 +172,7 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
>  
>  	voltage_tries = 1;
>  	max_vswing_tries = 0;
> +	cr_tries = 0;
>  	for (;;) {
>  		uint8_t link_status[DP_LINK_STATUS_SIZE];
>  
> @@ -215,6 +216,11 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
>  		if (intel_dp_link_max_vswing_reached(intel_dp))
>  			++max_vswing_tries;
>  
> +		if (cr_tries == 9) {
> +			DRM_ERROR("Failed clock recovery 10 times, giving up!\n");
> +			return false;
> +		}
> +		++cr_tries;

If I understood correctly this is a global thing for the for(;;) right?

Shouldn't we make then like a:

- for(;;)
+ for(cr_tries = 0; cr_tries < 10; cr_tries++)
	{
	}

+ DRM_ERROR("Failed clock recovery 10 times, giving up!\n"); 
+ return false;
}

Thanks,
Rodrigo.

>  	}
>  }
>  
> -- 
> 1.9.1
> 
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