Re: [PATCH 08/17] drm/i915: Wait for PHY port ready before link training on VLV/CHV

Todd Previte
2014-10-22T15:10:31Z

On 10/16/2014 11:27 AM, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> There's no point in checking if the data lanes came out of reset after
> link training. If the data lanes aren't ready link training will fail
> anyway.
>
> Suggested-by: Todd Previte <tprevite@gmail.com>
> Cc: Todd Previte <tprevite@gmail.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
> If Todd has a better patch with better description we can use that one
> instead of my version. But at least I think the spot where I put the
> vlv_wait_port_ready() is the right one. We could perhaps skip the link
> training attempt entirely if the port is already stuck.
>
> drivers/gpu/drm/i915/intel_dp.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 4c8f169..6f568b4 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -2550,6 +2550,9 @@ static void intel_enable_dp(struct intel_encoder *encoder)
>
> pps_unlock(intel_dp);
>
> + if (IS_VALLEYVIEW(dev))
> + vlv_wait_port_ready(dev_priv, dp_to_dig_port(intel_dp));
> +
> intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
> intel_dp_start_link_train(intel_dp);
> intel_dp_complete_link_train(intel_dp);
> @@ -2689,8 +2692,6 @@ static void vlv_pre_enable_dp(struct intel_encoder *encoder)
> mutex_unlock(&dev_priv->dpio_lock);
>
> intel_enable_dp(encoder);
> -
> - vlv_wait_port_ready(dev_priv, dport);
> }
>
> static void vlv_dp_pre_pll_enable(struct intel_encoder *encoder)
> @@ -2783,8 +2784,6 @@ static void chv_pre_enable_dp(struct intel_encoder *encoder)
> mutex_unlock(&dev_priv->dpio_lock);
>
> intel_enable_dp(encoder);
> -
> - vlv_wait_port_ready(dev_priv, dport);
> }
>
> static void chv_dp_pre_pll_enable(struct intel_encoder *encoder)

We should definitely skip link training if the PHYs are down. There's
going to be a WARN when wait_port_ready() fails so we'll be well aware
that something went wrong. Spamming dmesg with errors/WARNs from trying
to train the link after that is really counterproductive, since we
already know there's no way link training could succeed.

-T