linux-kernel - Re: [PATCH v3] drm/i915/display/lspcon: Increase LSPCON mode settle timeout

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Message-ID: <87r0mdgx96.fsf@intel.com>
Date:   Mon, 02 Oct 2023 13:00:05 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Pablo Ceballos <pceballos@...gle.com>,
        Ankit K Nautiyal <ankit.k.nautiyal@...el.com>
Cc:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Pablo Ceballos <pceballos@...gle.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, imre.deak@...ux.intel.com
Subject: Re: [PATCH v3] drm/i915/display/lspcon: Increase LSPCON mode settle
 timeout

On Wed, 16 Aug 2023, Pablo Ceballos <pceballos@...gle.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.
>
> Signed-off-by: Pablo Ceballos <pceballos@...gle.com>

Please file the issue at [1] as requested before, and reference it in
the commit message.

[1] https://gitlab.freedesktop.org/drm/intel/-/issues/new

> ---
>
> V2: Added more details in the commit message
> V3: Only apply the increased timeout if the vendor is Parade
>
> drivers/gpu/drm/i915/display/intel_lspcon.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_lspcon.c b/drivers/gpu/drm/i915/display/intel_lspcon.c
> index bb3b5355a0d9..b07eab84cc63 100644
> --- a/drivers/gpu/drm/i915/display/intel_lspcon.c
> +++ b/drivers/gpu/drm/i915/display/intel_lspcon.c
> @@ -153,6 +153,24 @@ static enum drm_lspcon_mode lspcon_get_current_mode(struct intel_lspcon *lspcon)
>  	return current_mode;
>  }
>  
> +static u32 lspcon_get_mode_settle_timeout(struct intel_lspcon *lspcon)
> +{
> +	u32 timeout_ms = 400;

Please use plain int for plain numbers. There's nothing u32 about this.

> +
> +	/*
> +	 * 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.
> +	 */
> +	if (lspcon->vendor == LSPCON_VENDOR_PARADE)
> +		timeout_ms = 800;
> +
> +	return timeout_ms;

All of the above is just

	return lspcon->vendor == LSPCON_VENDOR_PARADE ? 800 : 400;

BR,
Jani.

> +}
> +
> +
>  static enum drm_lspcon_mode lspcon_wait_mode(struct intel_lspcon *lspcon,
>  					     enum drm_lspcon_mode mode)
>  {
> @@ -167,7 +185,8 @@ static enum drm_lspcon_mode lspcon_wait_mode(struct intel_lspcon *lspcon,
>  	drm_dbg_kms(&i915->drm, "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_err(&i915->drm, "LSPCON mode hasn't settled\n");

-- 
Jani Nikula, Intel