Re: [PATCH v3] drm/i915/dp: Give up link training clock recovery after 10 failed attempts

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Mon, Jul 16, 2018 at 11:14:45AM -0700, Nathan Ciobanu wrote:
> Limit the link training clock recovery loop to 10 failed attempts at
> LANEx_CR_DONE per DP 1.4 spec section 3.5.1.2.2.

Thanks... so this made me look to DP 1.3 and DP 1.4 differences here.
Are we already addressing all new conditions?

I wonder if that should be at drm level.

I noticed that one difference, 100us wait difference is already
addressed there at drm level...

> Some USB-C MST hubs
> cause us to get stuck in this loop indefinitely requesting
> 
>     voltage swing: 0, pre-emphasis level: 2
>     voltage swing: 1, pre-emphasis level: 2
>     voltage swing: 0, pre-emphasis level: 3
> 
> over and over: max_vswing is never reached, drm_dp_clock_recovery_ok()
> never returns true and voltage_tries always gets reset to 1. The driver
> sends those values to the hub but the hub keeps requesting new values
> every time in the pattern shown above.
> 
> Changes in v2:
>     - updated commit message (DK, Manasi)
>     - defined DP_DP14_MAX_CR_TRIES (Marc)
>     - made the loop iterate for max 10 times (Rodrigo, Marc)
> 
> Changes in v3:
>     - changed error message to use DP_DP14_MAX_CR_TRIES
> 
> Signed-off-by: Nathan Ciobanu <nathan.d.ciobanu@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp_link_training.c | 7 +++++--
>  include/drm/drm_dp_helper.h                   | 1 +
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> index 4da6e33c7fa1..4bfba65c431c 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;
>  
> @@ -172,7 +172,7 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
>  
>  	voltage_tries = 1;
>  	max_vswing_tries = 0;
> -	for (;;) {
> +	for (cr_tries = 0; cr_tries < DP_DP14_MAX_CR_TRIES; ++cr_tries) {

I know that I was the on that asked you to make this global here,
but just now with better spec pointers and definition is that I noticed
that this is only for DP 1.4 spec while this code here runs for all
DP...  So we need to change in a way that we check the spec version somehow...

and possibly at drm level?!

>  		uint8_t link_status[DP_LINK_STATUS_SIZE];
>  
>  		drm_dp_link_train_clock_recovery_delay(intel_dp->dpcd);
> @@ -216,6 +216,9 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
>  			++max_vswing_tries;
>  
>  	}
> +	DRM_ERROR("Failed clock recovery %d times, giving up!\n",
> +		  DP_DP14_MAX_CR_TRIES);
> +	return false;
>  }
>  
>  /*
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index c01564991a9f..2303ad8ed24e 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -820,6 +820,7 @@
>  
>  #define DP_DP13_DPCD_REV                    0x2200
>  #define DP_DP13_MAX_LINK_RATE               0x2201
> +#define DP_DP14_MAX_CR_TRIES                10
>  
>  #define DP_DPRX_FEATURE_ENUMERATION_LIST    0x2210  /* DP 1.3 */
>  # define DP_GTC_CAP					(1 << 0)  /* DP 1.3 */
> -- 
> 1.9.1
> 
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