Re: [PATCH v3 4/4] drm/bridge: parade-ps8640: Handle DP AUX more properly

On 10/05/2022 22:29, Douglas Anderson wrote:

While it works, for the most part, to assume that the panel has finished probing when devm_of_dp_aux_populate_ep_devices() returns, it's a bit fragile. This is talked about at length in commit a1e3667a9835 ("drm/bridge: ti-sn65dsi86: Promote the AUX channel to its own sub-dev").

When reviewing the ps8640 code, I managed to convince myself that it was OK not to worry about it there and that maybe it wasn't really _that_ fragile. However, it turns out that it really is. Simply hardcoding panel_edp_probe() to return -EPROBE_DEFER was enough to put the boot process into an infinite loop. I believe this manages to trip the same issues that we used to trip with the main MSM code where something about our actions trigger Linux to re-probe previously deferred devices right away and each time we try again we re-trigger Linux to re-probe.

Let's fix this using the callback introduced in the patch ("drm/dp: Callbacks to make it easier for drivers to use DP AUX bus properly"). When using the new callback, we have to be a little careful. The probe_done() callback is no longer always called in the context of our probe routine. That means we can't rely on being able to return -EPROBE_DEFER from it. We re-jigger the order of things a bit to account for that.

With this change, the device still boots (though obviously the panel doesn't come up) if I force panel-edp to always return -EPROBE_DEFER. If I fake it and make the panel probe exactly once it also works.

Signed-off-by: Douglas Anderson dianders@chromium.org

Reviewed-by: Dmitry Baryshkov dmitry.baryshkov@linaro.org

---

Changes in v3:

• Adapt to v3 changes in aux bus.
• Use devm_drm_bridge_add() to simplify.

Changes in v2:

• Rewrote atop new method introduced by patch #1.

  drivers/gpu/drm/bridge/parade-ps8640.c | 74 ++++++++++++++++---------- 1 file changed, 46 insertions(+), 28 deletions(-)

diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c index e2467e58b5b7..ff4227f6d800 100644 --- a/drivers/gpu/drm/bridge/parade-ps8640.c +++ b/drivers/gpu/drm/bridge/parade-ps8640.c @@ -537,7 +537,7 @@ static const struct drm_bridge_funcs ps8640_bridge_funcs = { .pre_enable = ps8640_pre_enable, };

-static int ps8640_bridge_host_attach(struct device *dev, struct ps8640 *ps_bridge) +static int ps8640_bridge_get_dsi_resources(struct device *dev, struct ps8640 *ps_bridge) { struct device_node *in_ep, *dsi_node; struct mipi_dsi_device *dsi; @@ -576,13 +576,40 @@ static int ps8640_bridge_host_attach(struct device *dev, struct ps8640 *ps_bridg dsi->format = MIPI_DSI_FMT_RGB888; dsi->lanes = NUM_MIPI_LANES;

• return devm_mipi_dsi_attach(dev, dsi);

• return 0;

+}

+static int ps8640_bridge_link_panel(struct drm_dp_aux *aux) +{

• struct ps8640 *ps_bridge = aux_to_ps8640(aux);

• struct device *dev = aux->dev;

• struct device_node *np = dev->of_node;

• int ret;

• /*

• * NOTE about returning -EPROBE_DEFER from this function: if we
  

• * return an error (most relevant to -EPROBE_DEFER) it will only
  

• * be passed out to ps8640_probe() if it called this directly (AKA the
  

• * panel isn't under the "aux-bus" node). That should be fine because
  

• * if the panel is under "aux-bus" it's guaranteed to have probed by
  

• * the time this function has been called.
  

• */
  

• /* port@1 is ps8640 output port */

• ps_bridge->panel_bridge = devm_drm_of_get_bridge(dev, np, 1, 0);

• if (IS_ERR(ps_bridge->panel_bridge))

• return PTR_ERR(ps_bridge->panel_bridge);
  

• ret = devm_drm_bridge_add(dev, &ps_bridge->bridge);

• if (ret)

• return ret;
  

• return devm_mipi_dsi_attach(dev, ps_bridge->dsi); }

  static int ps8640_probe(struct i2c_client *client) { struct device *dev = &client->dev;

• struct device_node *np = dev->of_node; struct ps8640 *ps_bridge; int ret; u32 i;

@@ -623,6 +650,14 @@ static int ps8640_probe(struct i2c_client *client) if (!ps8640_of_panel_on_aux_bus(&client->dev)) ps_bridge->bridge.ops = DRM_BRIDGE_OP_EDID;

• /*

• * Get MIPI DSI resources early. These can return -EPROBE_DEFER so
  

• * we want to get them out of the way sooner.
  

• */
  

• ret = ps8640_bridge_get_dsi_resources(&client->dev, ps_bridge);

• if (ret)

• return ret;
  

• ps_bridge->page[PAGE0_DP_CNTL] = client;

  ps_bridge->regmap[PAGE0_DP_CNTL] = devm_regmap_init_i2c(client, ps8640_regmap_config);

@@ -665,35 +700,19 @@ static int ps8640_probe(struct i2c_client *client) if (ret) return ret;

• devm_of_dp_aux_populate_ep_devices(&ps_bridge->aux);

• ret = devm_of_dp_aux_populate_bus(&ps_bridge->aux, ps8640_bridge_link_panel);

• /* port@1 is ps8640 output port */
• ps_bridge->panel_bridge = devm_drm_of_get_bridge(dev, np, 1, 0);
• if (IS_ERR(ps_bridge->panel_bridge))

• return PTR_ERR(ps_bridge->panel_bridge);
  

• drm_bridge_add(&ps_bridge->bridge);
• ret = ps8640_bridge_host_attach(dev, ps_bridge);
• if (ret)

• goto err_bridge_remove;
  

• return 0;

• /*

• * If devm_of_dp_aux_populate_bus() returns -ENODEV then it's up to
  

• * usa to call ps8640_bridge_link_panel() directly. NOTE: in this case
  

• * the function is allowed to -EPROBE_DEFER.
  

• */
  

• if (ret == -ENODEV)

• return ps8640_bridge_link_panel(&ps_bridge->aux);
  
  

-err_bridge_remove:

• drm_bridge_remove(&ps_bridge->bridge); return ret; }

-static int ps8640_remove(struct i2c_client *client) -{

• struct ps8640 *ps_bridge = i2c_get_clientdata(client);
• drm_bridge_remove(&ps_bridge->bridge);
• return 0;

-}

• static const struct of_device_id ps8640_match[] = { { .compatible = "parade,ps8640" }, { }

@@ -702,7 +721,6 @@ MODULE_DEVICE_TABLE(of, ps8640_match);

static struct i2c_driver ps8640_driver = { .probe_new = ps8640_probe,

• .remove = ps8640_remove, .driver = { .name = "ps8640", .of_match_table = ps8640_match,