linux-kernel - Re: [RFT PATCH v2 3/3] drm/msm/dsi: More properly handle errors in regards to dsi_mgr_bridge_power

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Message-ID: <263e4bf2-6ade-600b-0fb6-e0a738ce830f@linaro.org>
Date:   Tue, 28 Feb 2023 03:25:54 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>,
        dri-devel@...ts.freedesktop.org, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Sean Paul <sean@...rly.run>, Jonas Karlman <jonas@...boo.se>,
        Vinod Koul <vkoul@...nel.org>,
        Robert Foss <robert.foss@...aro.org>,
        linux-arm-msm@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>,
        freedreno@...ts.freedesktop.org,
        Stephen Boyd <swboyd@...omium.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFT PATCH v2 3/3] drm/msm/dsi: More properly handle errors in
 regards to dsi_mgr_bridge_power_on()

On 01/02/2023 00:18, Douglas Anderson wrote:
> In commit 7d8e9a90509f ("drm/msm/dsi: move DSI host powerup to modeset
> time") the error handling with regards to dsi_mgr_bridge_power_on()
> got a bit worse. Specifically if we failed to power the bridge on then
> nothing would really notice. The modeset function couldn't return an
> error and thus we'd blindly go forward and try to do the pre-enable.
> 
> In commit ec7981e6c614 ("drm/msm/dsi: don't powerup at modeset time
> for parade-ps8640") we added a special case to move the powerup back
> to pre-enable time for ps8640. When we did that, we didn't try to
> recover the old/better error handling just for ps8640.
> 
> In the patch ("drm/msm/dsi: Stop unconditionally powering up DSI hosts
> at modeset") we've now moved the powering up back to exclusively being
> during pre-enable. That means we can add the better error handling
> back in, so let's do it. To do so we'll add a new function
> dsi_mgr_bridge_power_off() that's matches how errors were handled
> prior to commit 7d8e9a90509f ("drm/msm/dsi: move DSI host powerup to
> modeset time").
> 
> NOTE: Now that we have dsi_mgr_bridge_power_off(), it feels as if we
> should be calling it in dsi_mgr_bridge_post_disable(). That would make
> some sense, but doing so would change the current behavior and thus
> should be a separate patch. Specifically:
> * dsi_mgr_bridge_post_disable() always calls dsi_mgr_phy_disable()
>    even in the slave-DSI case of bonded DSI. We'd need to add special
>    handling for this if it's truly needed.
> * dsi_mgr_bridge_post_disable() calls msm_dsi_phy_pll_save_state()
>    midway through the poweroff.
> * dsi_mgr_bridge_post_disable() has a different order of some of the
>    poweroffs / IRQ disables.
> For now we'll leave dsi_mgr_bridge_post_disable() alone.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

-- 
With best wishes
Dmitry