[PATCH 07/15] drm/dp: Do not busy-loop during link training

[Lyude Paul]

On Tue, 2019-10-15 at 16:35 +0200, Thierry Reding wrote:
> From: Thierry Reding <treding at nvidia.com>
> 
> Use microsecond sleeps for the clock recovery and channel equalization
> delays during link training. The duration of these delays can be from
> 100 us up to 16 ms. It is rude to busy-loop for that amount of time.
> 
> While at it, also convert to standard coding style by putting the
> opening braces in a function definition on a new line.
> 
> v2: use correct multiplier for training delays (Philipp Zabel)
> 
> Signed-off-by: Thierry Reding <treding at nvidia.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 30 ++++++++++++++++++------------
>  1 file changed, 18 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c
> b/drivers/gpu/drm/drm_dp_helper.c
> index 8f2d7c4850ca..ad2671d2ee8f 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -120,33 +120,39 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8
> link_status[DP_LINK_STATUS_SI
>  }
>  EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis);
>  
> -void drm_dp_link_train_clock_recovery_delay(const u8
> dpcd[DP_RECEIVER_CAP_SIZE]) {
> -	int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> -			  DP_TRAINING_AUX_RD_MASK;
> +void drm_dp_link_train_clock_recovery_delay(const u8
> dpcd[DP_RECEIVER_CAP_SIZE])
> +{
> +	unsigned int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> +					DP_TRAINING_AUX_RD_MASK;

Did you mean to put this conversion from signed to unsigned in the previous
patch?

>  
>  	if (rd_interval > 4)
> -		DRM_DEBUG_KMS("AUX interval %d, out of range (max 4)\n",
> +		DRM_DEBUG_KMS("AUX interval %u, out of range (max 4)\n",
>  			      rd_interval);
>  
>  	if (rd_interval == 0 || dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14)
> -		udelay(100);
> +		rd_interval = 100;
>  	else
> -		mdelay(rd_interval * 4);
> +		rd_interval *= 4 * USEC_PER_MSEC;
> +
> +	usleep_range(rd_interval, rd_interval * 2);
>  }
>  EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
>  
> -void drm_dp_link_train_channel_eq_delay(const u8
> dpcd[DP_RECEIVER_CAP_SIZE]) {
> -	int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> -			  DP_TRAINING_AUX_RD_MASK;
> +void drm_dp_link_train_channel_eq_delay(const u8
> dpcd[DP_RECEIVER_CAP_SIZE])
> +{
> +	unsigned int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> +					DP_TRAINING_AUX_RD_MASK;
>  
>  	if (rd_interval > 4)
> -		DRM_DEBUG_KMS("AUX interval %d, out of range (max 4)\n",
> +		DRM_DEBUG_KMS("AUX interval %u, out of range (max 4)\n",
>  			      rd_interval);
>  
>  	if (rd_interval == 0)
> -		udelay(400);
> +		rd_interval = 400;
>  	else
> -		mdelay(rd_interval * 4);
> +		rd_interval *= 4 * USEC_PER_MSEC;
> +
> +	usleep_range(rd_interval, rd_interval * 2);
>  }
>  EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
>  
-- 
Cheers,
	Lyude Paul