linux-kernel - Re: [PATCH v2 2/2] drm/atomic: Force bridge self-refresh-exit on CRTC switch

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Date:   Tue, 01 Mar 2022 11:34:46 +0800
From:   Liu Ying <victor.liu@....nxp.com>
To:     Brian Norris <briannorris@...omium.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>
Cc:     dri-devel@...ts.freedesktop.org, Sean Paul <seanpaul@...omium.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Sean Paul <sean@...rly.run>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Heiko Stuebner <heiko@...ech.de>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] drm/atomic: Force bridge self-refresh-exit on
 CRTC switch

On Mon, 2022-02-28 at 12:25 -0800, Brian Norris wrote:
> It's possible to change which CRTC is in use for a given
> connector/encoder/bridge while we're in self-refresh without fully
> disabling the connector/encoder/bridge along the way. This can confuse
> the bridge encoder/bridge, because
> (a) it needs to track the SR state (trying to perform "active"
>     operations while the panel is still in SR can be Bad(TM)); and
> (b) it tracks the SR state via the CRTC state (and after the switch, the
>     previous SR state is lost).
> 
> Thus, we need to either somehow carry the self-refresh state over to the
> new CRTC, or else force an encoder/bridge self-refresh transition during
> such a switch.
> 
> I choose the latter, so we disable the encoder (and exit PSR) before
> attaching it to the new CRTC (where we can continue to assume a clean
> (non-self-refresh) state).
> 
> This fixes PSR issues seen on Rockchip RK3399 systems with
> drivers/gpu/drm/bridge/analogix/analogix_dp_core.c.
> 
> Change in v2:
> 
> - Drop "->enable" condition; this could possibly be "->active" to
>   reflect the intended hardware state, but it also is a little
>   over-specific. We want to make a transition through "disabled" any
>   time we're exiting PSR at the same time as a CRTC switch.

Cool. I don't see any particular issue regarding the drop.

Liu Ying

>   (Thanks Liu Ying)
> 
> Cc: Liu Ying <victor.liu@....nxp.com>
> Cc: <stable@...r.kernel.org>
> Fixes: 1452c25b0e60 ("drm: Add helpers to kick off self refresh mode in drivers")
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 9603193d2fa1..987e4b212e9f 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1011,9 +1011,19 @@ crtc_needs_disable(struct drm_crtc_state *old_state,
>  		return drm_atomic_crtc_effectively_active(old_state);
>  
>  	/*
> -	 * We need to run through the crtc_funcs->disable() function if the CRTC
> -	 * is currently on, if it's transitioning to self refresh mode, or if
> -	 * it's in self refresh mode and needs to be fully disabled.
> +	 * We need to disable bridge(s) and CRTC if we're transitioning out of
> +	 * self-refresh and changing CRTCs at the same time, because the
> +	 * bridge tracks self-refresh status via CRTC state.
> +	 */
> +	if (old_state->self_refresh_active &&
> +	    old_state->crtc != new_state->crtc)
> +		return true;
> +
> +	/*
> +	 * We also need to run through the crtc_funcs->disable() function if
> +	 * the CRTC is currently on, if it's transitioning to self refresh
> +	 * mode, or if it's in self refresh mode and needs to be fully
> +	 * disabled.
>  	 */
>  	return old_state->active ||
>  	       (old_state->self_refresh_active && !new_state->active) ||