linux-kernel - Re: drm/bridge: adv7511: Attach next bridge without creating connector

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Message-ID: <4b6e49ee-d2fd-4e54-88d5-ab06d8ebf644@bosc.ac.cn>
Date: Tue, 14 May 2024 00:26:15 +0800
From: Sui Jingfeng <suijingfeng@...c.ac.cn>
To: Liu Ying <victor.liu@....com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Cc: andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org,
 Laurent.pinchart@...asonboard.com, jonas@...boo.se,
 jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com,
 mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
 dmitry.baryshkov@...aro.org, biju.das.jz@...renesas.com, aford173@...il.com,
 bli@...g-olufsen.dk, robh@...nel.org, jani.nikula@...el.com
Subject: Re: drm/bridge: adv7511: Attach next bridge without creating
 connector

Hi,


On 5/13/24 16:02, Liu Ying wrote:
> The connector is created by either this ADV7511 bridge driver or
> any DRM device driver/previous bridge driver, so this ADV7511
> bridge driver should not let the next bridge driver create connector.
> 
> If the next bridge is a HDMI connector, the next bridge driver
> would fail to attach bridge from display_connector_attach() without
> the DRM_BRIDGE_ATTACH_NO_CONNECTOR flag.
> 
> Add that flag to drm_bridge_attach() function call in
> adv7511_bridge_attach() to fix the issue.
> 
> This fixes the issue where the HDMI connector bridge fails to attach
> to the previous ADV7535 bridge on i.MX8MP EVK platform:
> 
> [    2.216442] [drm:drm_bridge_attach] *ERROR* failed to attach bridge /hdmi-connector to encoder None-37: -22
> [    2.220675] mmc1: SDHCI controller on 30b50000.mmc [30b50000.mmc] using ADMA
> [    2.226262] [drm:drm_bridge_attach] *ERROR* failed to attach bridge /soc@...us@...00000/i2c@...30000/hdmi@3d to encoder None-37: -22
> [    2.245204] [drm:drm_bridge_attach] *ERROR* failed to attach bridge /soc@...us@...00000/dsi@...60000 to encoder None-37: -22
> [    2.256445] imx-lcdif 32e80000.display-controller: error -EINVAL: Failed to attach bridge for endpoint0
> [    2.265850] imx-lcdif 32e80000.display-controller: error -EINVAL: Cannot connect bridge
> [    2.274009] imx-lcdif 32e80000.display-controller: probe with driver imx-lcdif failed with error -22
> 
> Fixes: 14b3cdbd0e5b ("drm/bridge: adv7511: make it honour next bridge in DT")
> Signed-off-by: Liu Ying <victor.liu@....com>
> ---
>   drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> index dd21b81bd28f..66ccb61e2a66 100644
> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> @@ -953,7 +953,8 @@ static int adv7511_bridge_attach(struct drm_bridge *bridge,
>   	int ret = 0;
>   
>   	if (adv->next_bridge) {
> -		ret = drm_bridge_attach(bridge->encoder, adv->next_bridge, bridge, flags);
> +		ret = drm_bridge_attach(bridge->encoder, adv->next_bridge, bridge,
> +					flags | DRM_BRIDGE_ATTACH_NO_CONNECTOR);

As a side note, I think, maybe you could do better in the future.

If we know that the KMS display driver side has the HDMI connector
already created for us, we should pass DRM_BRIDGE_ATTACH_NO_CONNECTOR
from the root KMS driver side. Which is to forbidden all potential
drm bridge drivers to create a connector in the middle.

The KMS display driver side could parse the DT to know if there is
a hdmi connector, or merely just hdmi connector device node, or
something else.

However, other maintainer and/or reviewer's opinion are of cause
more valuable. I send a A-b because I thought the bug is urgency
and it's probably more important to solve this bug first. And
maybe you can Cc: <stable@...r.kernel.org> if you like.

Thanks.

>   		if (ret)
>   			return ret;
>   	}

-- 
Best regards
Sui Jingfeng