linux-kernel - Re: [RFC] dcss: fix attaching to sn56dsi86 bridge

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Message-ID: <20201125065549.t36mg4nzyoug72yu@fsr-ub1864-141>
Date:   Wed, 25 Nov 2020 08:55:49 +0200
From:   Laurentiu Palcu <laurentiu.palcu@....nxp.com>
To:     "Lukas F. Hartmann" <lukas@...re.com>
Cc:     agx@...xcpu.org, laurentiu.palcu@....com,
        Lucas Stach <l.stach@...gutronix.de>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] dcss: fix attaching to sn56dsi86 bridge

Hi Lukas,

On Tue, Nov 24, 2020 at 06:19:57PM +0100, Lukas F. Hartmann wrote:
> The sn56dsi86 DSI to eDP bridge driver does not support attaching
> without a drm connector.

I think the SN65DSI86 driver is exactly what you should focus on, so
that it works when connector is optional. The ADV7511/ADV7533/ADV7535
driver provides the best example on how it should be done.

Thanks,
laurentiu

> This patch makes the attachment work. Required for the display chain
> in MNT Reform 2.0 (DCSS->NWL DSI->SN56DSI86->EDP).
> 
> Signed-off-by: Lukas F. Hartmann <lukas@...re.com>
> ---
>  drivers/gpu/drm/imx/dcss/dcss-kms.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/imx/dcss/dcss-kms.c b/drivers/gpu/drm/imx/dcss/dcss-kms.c
> index 135a62366..4967f828b 100644
> --- a/drivers/gpu/drm/imx/dcss/dcss-kms.c
> +++ b/drivers/gpu/drm/imx/dcss/dcss-kms.c
> @@ -82,6 +82,7 @@ static int dcss_kms_bridge_connector_init(struct dcss_kms_dev *kms)
>  	struct drm_crtc *crtc = (struct drm_crtc *)&kms->crtc;
>  	struct drm_panel *panel;
>  	struct drm_bridge *bridge;
> +	struct drm_connector_list_iter iter;
>  	int ret;
> 
>  	ret = drm_of_find_panel_or_bridge(ddev->dev->of_node, 0, 0,
> @@ -104,19 +105,19 @@ static int dcss_kms_bridge_connector_init(struct dcss_kms_dev *kms)
>  		return ret;
>  	}
> 
> -	ret = drm_bridge_attach(encoder, bridge, NULL,
> -				DRM_BRIDGE_ATTACH_NO_CONNECTOR);
> +	ret = drm_bridge_attach(encoder, bridge, NULL, 0);
>  	if (ret < 0) {
>  		dev_err(ddev->dev, "Unable to attach bridge %pOF\n",
>  			bridge->of_node);
>  		return ret;
>  	}
> 
> -	kms->connector = drm_bridge_connector_init(ddev, encoder);
> -	if (IS_ERR(kms->connector)) {
> -		dev_err(ddev->dev, "Unable to create bridge connector.\n");
> -		return PTR_ERR(kms->connector);
> -	}
> +	/*
> +	 * This hack to look up the connector is copied from mxsfb.
> +	 */
> +	drm_connector_list_iter_begin(ddev, &iter);
> +	kms->connector = drm_connector_list_iter_next(&iter);
> +	drm_connector_list_iter_end(&iter);
> 
>  	drm_connector_attach_encoder(kms->connector, encoder);
> 
> --
> 2.28.0