Re: [PATCH v4 20/27] drm/bridge: ti-sn65dsi86: Promote the AUX channel to its own sub-dev

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Fri 16 Apr 17:39 CDT 2021, Douglas Anderson wrote:

> We'd like to be able to expose the DDC-over-AUX channel bus to our
> panel. This gets into a chicken-and-egg problem because:
> - The panel wants to get its DDC at probe time.
> - The ti-sn65dsi86 MIPI-to-eDP bridge code, which provides the DDC
>   bus, wants to get the panel at probe time.
> 
> By using a sub device we can fully create the AUX channel bits so that
> the panel can get them. Then the panel can finish probing and the
> bridge can probe.
> 
> To accomplish this, we also move registering the AUX channel out of
> the bridge's attach code and do it right at probe time. We use devm to
> manage cleanup.
> 
> NOTE: there's a little bit of a trick here. Though the AUX channel can
> run without the MIPI-to-eDP bits of the code, the MIPI-to-eDP bits
> can't run without the AUX channel. We could come up a complicated
> signaling scheme (have the MIPI-to-eDP bits return EPROBE_DEFER for a
> while or wait on some sort of completion), but it seems simple enough
> to just not even bother creating the bridge device until the AUX
> channel probes. That's what we'll do.
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
> (no changes since v1)
> 
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 82 ++++++++++++++++++++-------
>  1 file changed, 63 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index 875e5dbe6594..8253098bcdbf 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -116,6 +116,7 @@
>   * struct ti_sn65dsi86 - Platform data for ti-sn65dsi86 driver.
>   * @bridge_aux:   AUX-bus sub device for MIPI-to-eDP bridge functionality.
>   * @gpio_aux:     AUX-bus sub device for GPIO controller functionality.
> + * @aux_aux:      AUX-bus sub device for eDP AUX channel functionality.
>   *
>   * @dev:          Pointer to the top level (i2c) device.
>   * @regmap:       Regmap for accessing i2c.
> @@ -148,6 +149,7 @@
>  struct ti_sn65dsi86 {
>  	struct auxiliary_device		bridge_aux;
>  	struct auxiliary_device		gpio_aux;
> +	struct auxiliary_device		aux_aux;
>  
>  	struct device			*dev;
>  	struct regmap			*regmap;
> @@ -483,18 +485,12 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge,
>  		return -EINVAL;
>  	}
>  
> -	ret = drm_dp_aux_register(&pdata->aux);
> -	if (ret < 0) {
> -		drm_err(bridge->dev, "Failed to register DP AUX channel: %d\n", ret);
> -		return ret;
> -	}
> -
>  	ret = drm_connector_init(bridge->dev, &pdata->connector,
>  				 &ti_sn_bridge_connector_funcs,
>  				 DRM_MODE_CONNECTOR_eDP);
>  	if (ret) {
>  		DRM_ERROR("Failed to initialize connector with drm\n");
> -		goto err_conn_init;
> +		return ret;
>  	}
>  
>  	drm_connector_helper_add(&pdata->connector,
> @@ -551,8 +547,6 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge,
>  	mipi_dsi_device_unregister(dsi);
>  err_dsi_host:
>  	drm_connector_cleanup(&pdata->connector);
> -err_conn_init:
> -	drm_dp_aux_unregister(&pdata->aux);
>  	return ret;
>  }
>  
> @@ -1316,11 +1310,6 @@ static int ti_sn_bridge_probe(struct auxiliary_device *adev,
>  	if (ret)
>  		return ret;
>  
> -	pdata->aux.name = "ti-sn65dsi86-aux";
> -	pdata->aux.dev = pdata->dev;
> -	pdata->aux.transfer = ti_sn_aux_transfer;
> -	drm_dp_aux_init(&pdata->aux);
> -
>  	pdata->bridge.funcs = &ti_sn_bridge_funcs;
>  	pdata->bridge.of_node = np;
>  
> @@ -1419,6 +1408,54 @@ static int ti_sn65dsi86_add_aux_device(struct ti_sn65dsi86 *pdata,
>  	return ret;
>  }
>  
> +static void ti_sn65dsi86_unregister_dp_aux(void *data)
> +{
> +	drm_dp_aux_unregister(data);
> +}
> +
> +static int ti_sn_aux_probe(struct auxiliary_device *adev,
> +			   const struct auxiliary_device_id *id)
> +{
> +	struct ti_sn65dsi86 *pdata = dev_get_drvdata(adev->dev.parent);
> +	int ret;
> +
> +	pdata->aux.name = "ti-sn65dsi86-aux";
> +	pdata->aux.dev = pdata->dev;
> +	pdata->aux.transfer = ti_sn_aux_transfer;
> +	drm_dp_aux_init(&pdata->aux);
> +
> +	ret = drm_dp_aux_register(&pdata->aux);
> +	if (ret < 0) {
> +		drm_err(pdata, "Failed to register DP AUX channel: %d\n", ret);
> +		return ret;
> +	}
> +	ret = devm_add_action_or_reset(&adev->dev,
> +				       ti_sn65dsi86_unregister_dp_aux, &pdata->aux);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * The eDP to MIPI bridge parts don't work until the AUX channel is
> +	 * setup so we don't add it in the main driver probe, we add it now.
> +	 */
> +	return ti_sn65dsi86_add_aux_device(pdata, &pdata->bridge_aux, "bridge");
> +}
> +
> +static const struct auxiliary_device_id ti_sn_aux_id_table[] = {
> +	{ .name = "ti_sn65dsi86.aux", },
> +	{},
> +};
> +
> +MODULE_DEVICE_TABLE(auxiliary, ti_sn_aux_id_table);
> +
> +static struct auxiliary_driver ti_sn_aux_driver = {
> +	.name = "aux",
> +	.probe = ti_sn_aux_probe,
> +	.id_table = ti_sn_aux_id_table,
> +};
> +
> +module_auxiliary_driver(ti_sn_aux_driver);

As with the earlier patch, please drop MODULE_DEVICE_TABLE() and rework
module_driver().

Regards,
Bjorn

> +
>  static int ti_sn65dsi86_probe(struct i2c_client *client,
>  			      const struct i2c_device_id *id)
>  {
> @@ -1477,10 +1514,11 @@ static int ti_sn65dsi86_probe(struct i2c_client *client,
>  	 * motiviation here is to solve the chicken-and-egg problem of probe
>  	 * ordering. The bridge wants the panel to be there when it probes.
>  	 * The panel wants its HPD GPIO (provided by sn65dsi86 on some boards)
> -	 * when it probes. There will soon be other devices (DDC I2C bus, PWM)
> -	 * that have the same problem. Having sub-devices allows the some sub
> -	 * devices to finish probing even if others return -EPROBE_DEFER and
> -	 * gets us around the problems.
> +	 * when it probes. The panel and maybe backlight might want the DDC
> +	 * bus. Soon the PWM provided by the bridge chip will have the same
> +	 * problem. Having sub-devices allows the some sub devices to finish
> +	 * probing even if others return -EPROBE_DEFER and gets us around the
> +	 * problems.
>  	 */
>  
>  	if (IS_ENABLED(CONFIG_OF_GPIO)) {
> @@ -1489,7 +1527,13 @@ static int ti_sn65dsi86_probe(struct i2c_client *client,
>  			return ret;
>  	}
>  
> -	return ti_sn65dsi86_add_aux_device(pdata, &pdata->bridge_aux, "bridge");
> +	/*
> +	 * NOTE: At the end of the AUX channel probe we'll add the aux device
> +	 * for the bridge. This is because the bridge can't be used until the
> +	 * AUX channel is there and this is a very simple solution to the
> +	 * dependency problem.
> +	 */
> +	return ti_sn65dsi86_add_aux_device(pdata, &pdata->aux_aux, "aux");
>  }
>  
>  static struct i2c_device_id ti_sn65dsi86_id[] = {
> -- 
> 2.31.1.368.gbe11c130af-goog
>