Re: [PATCH v3 06/13] drm/dp: Do not busy-loop during link training

From: Daniel Vetter <daniel@ffwll.ch>
To: Thierry Reding <thierry.reding@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v3 06/13] drm/dp: Do not busy-loop during link training
Date: Tue, 22 Oct 2019 16:04:48 +0200	[thread overview]
Message-ID: <20191022140447.GP11828@phenom.ffwll.local> (raw)
In-Reply-To: <20191021143437.1477719-7-thierry.reding@gmail.com>

On Mon, Oct 21, 2019 at 04:34:30PM +0200, Thierry Reding wrote:
> From: Thierry Reding <treding@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. Also switch to
> using an unsigned int for the AUX read interval to match the data type
> of the parameters to usleep_range().
> 
> v2: use correct multiplier for training delays (Philipp Zabel)
> v3: clarify data type change in commit message
> 
> Signed-off-by: Thierry Reding <treding@nvidia.com>

After you pointing out on irc that the default value isn't the same and me
having flash-backs ...

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  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..ac802b04f120 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 long 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 %lu, 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 long 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 %lu, 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);
>  
> -- 
> 2.23.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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