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Date:   Wed, 3 Jun 2020 02:51:39 +0300
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Adrian Ratiu <adrian.ratiu@collabora.com>
Cc:     linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linux-rockchip@lists.infradead.org,
        Andrzej Hajda <a.hajda@samsung.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@siol.net>,
        Heiko Stuebner <heiko@sntech.de>, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-imx@nxp.com,
        kernel@collabora.com, linux-stm32@st-md-mailman.stormreply.com
Subject: Re: [PATCH v8 04/10] drm: bridge: dw_mipi_dsi: allow bridge daisy
 chaining
Message-ID: <20200602235139.GS6547@pendragon.ideasonboard.com>
References: <20200427081952.3536741-1-adrian.ratiu@collabora.com>
 <20200427081952.3536741-5-adrian.ratiu@collabora.com>
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Hi Adrian,

Thank you for the patch.

On Mon, Apr 27, 2020 at 11:19:46AM +0300, Adrian Ratiu wrote:
> Up until now the assumption was that the synopsis dsi bridge will
> directly connect to an encoder provided by the platform driver, but
> the current practice for drivers is to leave the encoder empty via
> the simple encoder API and add their logic to their own drm_bridge.
> 
> Thus we need an ablility to connect the DSI bridge to another bridge
> provided by the platform driver, so we extend the dw_mipi_dsi bind()
> API with a new "previous bridge" arg instead of just hardcoding NULL.
> 
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
> ---
> New in v8.
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c   | 6 ++++--
>  drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c | 2 +-
>  include/drm/bridge/dw_mipi_dsi.h                | 5 ++++-
>  3 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> index 16fd87055e7b7..140ff40fa1b62 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> @@ -1456,11 +1456,13 @@ EXPORT_SYMBOL_GPL(dw_mipi_dsi_remove);
>  /*
>   * Bind/unbind API, used from platforms based on the component framework.
>   */
> -int dw_mipi_dsi_bind(struct dw_mipi_dsi *dsi, struct drm_encoder *encoder)
> +int dw_mipi_dsi_bind(struct dw_mipi_dsi *dsi,
> +		     struct drm_encoder *encoder,
> +		     struct drm_bridge *prev_bridge)
>  {
>  	int ret;
>  
> -	ret = drm_bridge_attach(encoder, &dsi->bridge, NULL, 0);
> +	ret = drm_bridge_attach(encoder, &dsi->bridge, prev_bridge, 0);

Please note that chaining of bridges doesn't work well if multiple
bridges in the chain try to create a connector. This is why a
DRM_BRIDGE_ATTACH_NO_CONNECTOR flag has been added, with a helper to
create a connector for a chain of bridges (drm_bridge_connector_init()).
This won't play well with the component framework. I would recommend
using the of_drm_find_bridge() instead in the rockchip driver, and
deprecating dw_mipi_dsi_bind().

>  	if (ret) {
>  		DRM_ERROR("Failed to initialize bridge with drm\n");
>  		return ret;
> diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c
> index 3feff0c45b3f7..83ef43be78135 100644
> --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c
> +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c
> @@ -929,7 +929,7 @@ static int dw_mipi_dsi_rockchip_bind(struct device *dev,
>  		return ret;
>  	}
>  
> -	ret = dw_mipi_dsi_bind(dsi->dmd, &dsi->encoder);
> +	ret = dw_mipi_dsi_bind(dsi->dmd, &dsi->encoder, NULL);
>  	if (ret) {
>  		DRM_DEV_ERROR(dev, "Failed to bind: %d\n", ret);
>  		return ret;
> diff --git a/include/drm/bridge/dw_mipi_dsi.h b/include/drm/bridge/dw_mipi_dsi.h
> index b0e390b3288e8..699b3531f5b36 100644
> --- a/include/drm/bridge/dw_mipi_dsi.h
> +++ b/include/drm/bridge/dw_mipi_dsi.h
> @@ -14,6 +14,7 @@
>  #include <drm/drm_modes.h>
>  
>  struct drm_display_mode;
> +struct drm_bridge;
>  struct drm_encoder;
>  struct dw_mipi_dsi;
>  struct mipi_dsi_device;
> @@ -62,7 +63,9 @@ struct dw_mipi_dsi *dw_mipi_dsi_probe(struct platform_device *pdev,
>  				      const struct dw_mipi_dsi_plat_data
>  				      *plat_data);
>  void dw_mipi_dsi_remove(struct dw_mipi_dsi *dsi);
> -int dw_mipi_dsi_bind(struct dw_mipi_dsi *dsi, struct drm_encoder *encoder);
> +int dw_mipi_dsi_bind(struct dw_mipi_dsi *dsi,
> +		     struct drm_encoder *encoder,
> +		     struct drm_bridge *prev_bridge);
>  void dw_mipi_dsi_unbind(struct dw_mipi_dsi *dsi);
>  void dw_mipi_dsi_set_slave(struct dw_mipi_dsi *dsi, struct dw_mipi_dsi *slave);
>  

-- 
Regards,

Laurent Pinchart