linux-kernel - Re: [PATCH v3] drm/msm/dsi: only powerup at modeset time if "early

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Message-ID: <e8d75148-22ee-5809-fc65-d0fb38ad4876@linaro.org>
Date:   Thu, 12 May 2022 23:58:59 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, Sean Paul <sean@...rly.run>,
        Stephen Boyd <swboyd@...omium.org>,
        Vinod Koul <vkoul@...nel.org>, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] drm/msm/dsi: only powerup at modeset time if
 "early_poweron" modparam

On 12/05/2022 23:52, Douglas Anderson wrote:
> Commit 7d8e9a90509f ("drm/msm/dsi: move DSI host powerup to modeset
> time") caused sc7180 Chromebooks that use the parade-ps8640 bridge
> chip to fail to turn the display back on after it turns off.
> 
> Unfortunately, it doesn't look easy to fix the parade-ps8640 driver to
> handle the new power sequence. The Linux driver has almost nothing in
> it and most of the logic for this bridge chip is in black-box firmware
> that the bridge chip uses.
> 
> Also unfortunately, reverting the patch will break "tc358762".
> 
> The long term solution here is probably Dave Stevenson's series [1]
> that would give more flexibility. However, that is likely not a quick
> fix.
> 
> For the short term, let's introduce a module parameter that selects
> between the two behaviors. This is a short term hack but at least can
> keep both users working. We'll default the value of the module
> parameter to the old behavior. Given that the old behavior has existed
> for longer it's probably a safer default.
> 
> [1] https://lore.kernel.org/r/cover.1646406653.git.dave.stevenson@raspberrypi.com
> 
> Fixes: 7d8e9a90509f ("drm/msm/dsi: move DSI host powerup to modeset time")
> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

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

Two minor issues below.

> ---
> 
> Changes in v3:
> - No longer a revert; now a module parameter.
> 
> Changes in v2:
> - Remove the mud from my face.
> 
>   drivers/gpu/drm/msm/dsi/dsi_manager.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> index 50b987658b1f..2bf4123ef5df 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> @@ -34,6 +34,10 @@ static struct msm_dsi_manager msm_dsim_glb;
>   #define IS_SYNC_NEEDED()	(msm_dsim_glb.is_sync_needed)
>   #define IS_MASTER_DSI_LINK(id)	(msm_dsim_glb.master_dsi_link_id == id)
>   
> +bool early_poweron;
> +MODULE_PARM_DESC(early_poweron, "Power DSI controller early");
> +module_param(early_poweron, bool, 0600);

Nit: dsi_early_poweron (to be clear that it related to DSI only).

I thought about suggesting 'dsi_no_early_poweron' instead to catch 
possible issues with other bridges. But... I think with Dave's series 
will have to enable bridges one by one, so it doesn't make real sense.

> +
>   static inline struct msm_dsi *dsi_mgr_get_dsi(int id)
>   {
>   	return msm_dsim_glb.dsi[id];
> @@ -389,6 +393,9 @@ static void dsi_mgr_bridge_pre_enable(struct drm_bridge *bridge)
>   	if (is_bonded_dsi && !IS_MASTER_DSI_LINK(id))
>   		return;
>   
> +	if (!early_poweron)
> +		dsi_mgr_bridge_power_on(bridge);
> +
>   	/* Always call panel functions once, because even for dual panels,
>   	 * there is only one drm_panel instance.
>   	 */
> @@ -570,7 +577,8 @@ static void dsi_mgr_bridge_mode_set(struct drm_bridge *bridge,
>   	if (is_bonded_dsi && other_dsi)
>   		msm_dsi_host_set_display_mode(other_dsi->host, adjusted_mode);
>   
> -	dsi_mgr_bridge_power_on(bridge);
> +	if (early_poweron)
> +		dsi_mgr_bridge_power_on(bridge);
>   }
>   
>   static enum drm_mode_status dsi_mgr_bridge_mode_valid(struct drm_bridge *bridge,


-- 
With best wishes
Dmitry