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

Bjorn Andersson
2021-04-23T15:00:01Z

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
>