linux-kernel - Re: [PATCH v3 3/4] drm/bridge: ti-sn65dsi86: Read EDID blob over DDC

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Date:   Thu, 18 Mar 2021 02:20:43 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Jonas Karlman <jonas@...boo.se>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Douglas Anderson <dianders@...omium.org>,
        Sean Paul <seanpaul@...omium.org>
Subject: Re: [PATCH v3 3/4] drm/bridge: ti-sn65dsi86: Read EDID blob over DDC

Hi Stephen,

Reviving a bit of an old thread, for a question.

On Mon, Nov 02, 2020 at 10:11:43AM -0800, Stephen Boyd wrote:
> Use the DDC connection to read the EDID from the eDP panel instead of
> relying on the panel to tell us the modes.
> 
> Reviewed-by: Douglas Anderson <dianders@...omium.org>
> Reviewed-by: Laurent Pinchart <Laurent.pinchart@...asonboard.com>
> Cc: Jonas Karlman <jonas@...boo.se>
> Cc: Jernej Skrabec <jernej.skrabec@...l.net>
> Cc: Sean Paul <seanpaul@...omium.org>
> Acked-by: Sam Ravnborg <sam@...nborg.org>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index 8276fa50138f..6b6e98ca2881 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -119,6 +119,7 @@
>   * @debugfs:      Used for managing our debugfs.
>   * @host_node:    Remote DSI node.
>   * @dsi:          Our MIPI DSI source.
> + * @edid:         Detected EDID of eDP panel.
>   * @refclk:       Our reference clock.
>   * @panel:        Our panel.
>   * @enable_gpio:  The GPIO we toggle to enable the bridge.
> @@ -144,6 +145,7 @@ struct ti_sn_bridge {
>  	struct drm_bridge		bridge;
>  	struct drm_connector		connector;
>  	struct dentry			*debugfs;
> +	struct edid			*edid;
>  	struct device_node		*host_node;
>  	struct mipi_dsi_device		*dsi;
>  	struct clk			*refclk;
> @@ -265,6 +267,23 @@ connector_to_ti_sn_bridge(struct drm_connector *connector)
>  static int ti_sn_bridge_connector_get_modes(struct drm_connector *connector)
>  {
>  	struct ti_sn_bridge *pdata = connector_to_ti_sn_bridge(connector);
> +	struct edid *edid = pdata->edid;
> +	int num, ret;
> +
> +	if (!edid) {
> +		pm_runtime_get_sync(pdata->dev);
> +		edid = pdata->edid = drm_get_edid(connector, &pdata->aux.ddc);
> +		pm_runtime_put(pdata->dev);

Is there any specific reason to use the indirect access method, compared
to the direct method that translates access to an I2C ancillary address
to an I2C-over-AUX transaction (see page 20 of SLLSEH2B) ? The direct
method seems it would be more efficient.

> +	}
> +
> +	if (edid && drm_edid_is_valid(edid)) {
> +		ret = drm_connector_update_edid_property(connector, edid);
> +		if (!ret) {
> +			num = drm_add_edid_modes(connector, edid);
> +			if (num)
> +				return num;
> +		}
> +	}
>  
>  	return drm_panel_get_modes(pdata->panel, connector);
>  }
> @@ -1245,6 +1264,7 @@ static int ti_sn_bridge_remove(struct i2c_client *client)
>  	if (!pdata)
>  		return -EINVAL;
>  
> +	kfree(pdata->edid);
>  	ti_sn_debugfs_remove(pdata);
>  
>  	of_node_put(pdata->host_node);

-- 
Regards,

Laurent Pinchart