linux-kernel - Re: [PATCH] drm/i915/dp: Send DPCD ON for MST before phy

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Message-ID: <20180405163853.GK5453@intel.com>
Date:   Thu, 5 Apr 2018 19:38:53 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Lyude Paul <lyude@...hat.com>
Cc:     intel-gfx@...ts.freedesktop.org,
        Dhinakaran Pandiyan <dhinakaran.pandiyan@...el.com>,
        Laura Abbott <labbott@...hat.com>, stable@...r.kernel.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915/dp: Send DPCD ON for MST before phy_up

On Wed, Apr 04, 2018 at 07:27:21PM -0400, Lyude Paul wrote:
> As it turns out, the aux block being off was not the real problem here,
> as transition from D3 to D0 is mandated by the DP spec to take a maximum
> of 1ms, whereas we're allowed a 100ms timeframe to respond to ESI irqs.
> The real problem here is a bit more subtle.
> 
> When doing a modeset where the problem of the sink timing out to our
> sideband requests when transitioning from D3 to D0 occurs, the timeout
> is from the aux block not coming on. However, nothing else times out
> other than the initial phy_up message because the DPCD on call in
> intel_ddi_enable_dp() ends up waking up the AUX block on the hub, not
> the phy_up sideband message. This means that the real fix we need is to
> use the DPMS on before sending a phy_up to ensure that the hub is ready
> to accept sideband messages.
> 
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@...el.com>
> Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> Cc: Laura Abbott <labbott@...hat.com>
> Cc: stable@...r.kernel.org
> Fixes: ad260ab32a4d9 ("drm/i915/dp: Write to SET_POWER dpcd to enable MST hub.")
> ---
>  drivers/gpu/drm/i915/intel_ddi.c    | 6 +++++-
>  drivers/gpu/drm/i915/intel_dp_mst.c | 1 +
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index a6672a9abd85..9bd675f73f7b 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -2324,7 +2324,11 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
>  		intel_prepare_dp_ddi_buffers(encoder, crtc_state);
>  
>  	intel_ddi_init_dp_buf_reg(encoder);
> -	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
> +	/* for MST, we do DPMS_ON outside of here so that DPMS_ON can happen
> +	 * before drm_dp_send_power_updown_phy()
> +	 */
> +	if (!intel_dp->is_mst)

Just 'is_mst' should do here.

And in general I'd like to see the enable and disable paths remain
symmetric. Ie. also move out the dpms call in the disable path (or
maybe move the phy_power_up/down in?).

> +		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
>  	intel_dp_start_link_train(intel_dp);
>  	if (port != PORT_A || INTEL_GEN(dev_priv) >= 9)
>  		intel_dp_stop_link_train(intel_dp);
> diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
> index c3de0918ee13..eff9a4eae1f0 100644
> --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> @@ -223,6 +223,7 @@ static void intel_mst_pre_enable_dp(struct intel_encoder *encoder,
>  
>  	DRM_DEBUG_KMS("active links %d\n", intel_dp->active_mst_links);
>  
> +	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
>  	drm_dp_send_power_updown_phy(&intel_dp->mst_mgr, connector->port, true);

This could use a comment to remind people that the order does matter.

>  	if (intel_dp->active_mst_links == 0)
>  		intel_dig_port->base.pre_enable(&intel_dig_port->base,
> -- 
> 2.14.3

-- 
Ville Syrjälä
Intel OTC