Re: [PATCH v4] drm/i915/display/lspcon: Increase LSPCON mode settle timeout

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 02 Oct 2023, Niko Tsirakis <ntsirakis@google.com> wrote:
> This is to eliminate all cases of "*ERROR* LSPCON mode hasn't settled",
> followed by link training errors. Intel engineers recommended increasing
> this timeout and that does resolve the issue.
>
> On some CometLake-based device designs the Parade PS175 takes more than
> 400ms to settle in PCON mode. 100 reboot trials on one device resulted
> in a median settle time of 440ms and a maximum of 444ms. Even after
> increasing the timeout to 500ms, 2% of devices still had this error. So
> this increases the timeout to 800ms.
>
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/9443
> Signed-off-by: Pablo Ceballos <pceballos@google.com>
> Signed-off-by: Niko Tsirakis <ntsirakis@google.com>

Thanks for the patch, pushed to drm-intel-next.

BR,
Jani.

> ---
>  drivers/gpu/drm/i915/display/intel_lspcon.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_lspcon.c b/drivers/gpu/drm/i915/display/intel_lspcon.c
> index dc1b35559afd..92536482e657 100644
> --- a/drivers/gpu/drm/i915/display/intel_lspcon.c
> +++ b/drivers/gpu/drm/i915/display/intel_lspcon.c
> @@ -116,6 +116,18 @@ static enum drm_lspcon_mode lspcon_get_current_mode(struct intel_lspcon *lspcon)
>  	return current_mode;
>  }
>  
> +static int lspcon_get_mode_settle_timeout(struct intel_lspcon *lspcon)
> +{
> +	/*
> +	 * On some CometLake-based device designs the Parade PS175 takes more
> +	 * than 400ms to settle in PCON mode. 100 reboot trials on one device
> +	 * resulted in a median settle time of 440ms and a maximum of 444ms.
> +	 * Even after increasing the timeout to 500ms, 2% of devices still had
> +	 * this error. So this sets the timeout to 800ms.
> +	 */
> +	return lspcon->vendor == LSPCON_VENDOR_PARADE ? 800 : 400;
> +}
> +
>  static enum drm_lspcon_mode lspcon_wait_mode(struct intel_lspcon *lspcon,
>  					     enum drm_lspcon_mode mode)
>  {
> @@ -128,7 +140,8 @@ static enum drm_lspcon_mode lspcon_wait_mode(struct intel_lspcon *lspcon,
>  	DRM_DEBUG_KMS("Waiting for LSPCON mode %s to settle\n",
>  		      lspcon_mode_name(mode));
>  
> -	wait_for((current_mode = lspcon_get_current_mode(lspcon)) == mode, 400);
> +	wait_for((current_mode = lspcon_get_current_mode(lspcon)) == mode,
> +		lspcon_get_mode_settle_timeout(lspcon));
>  	if (current_mode != mode)
>  		DRM_ERROR("LSPCON mode hasn't settled\n");

-- 
Jani Nikula, Intel