Re: [PATCH v3] drm/mediatek: mtk_dsi: Avoid EPROBE_DEFER loop with external bridge

AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx> · Thu, 27 Jan 2022 16:46:19 +0100

Il 27/01/22 16:21, Chun-Kuang Hu ha scritto:
Hi, Angelo:

AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx> 於
2022年1月27日 週四 下午10:36寫道：

DRM bridge drivers are now attaching their DSI device at probe time,
which requires us to register our DSI host in order to let the bridge
to probe: this recently started producing an endless -EPROBE_DEFER
loop on some machines that are using external bridges, like the
parade-ps8640, found on the ACER Chromebook R13.

Now that the DSI hosts/devices probe sequence is documented, we can
do adjustments to the mtk_dsi driver as to both fix now and make sure
to avoid this situation in the future: for this, following what is
documented in drm_bridge.c, move the mtk_dsi component_add() to the
mtk_dsi_ops.attach callback and delete it in the detach callback;
keeping in mind that we are registering a drm_bridge for our DSI,
which is only used/attached if the DSI Host is bound, it wouldn't
make sense to keep adding our bridge at probe time (as it would
be useless to have it if mtk_dsi_ops.attach() fails!), so also move
that one to the dsi host attach function (and remove it in detach).

Fixes: 209264a85707 ("drm/bridge: Document the probe issue with MIPI-DSI bridges")

The fixed tag should indicate the patch which cause the bug, but why a
patch just adding document would cause bug?
So no any patch cause bug? This patch just want to prevent a possible bug?


I think you've missed my previous message on v2, so I will paste it here:

unfortunately I couldn't find a valid commit for a Fixes tag. This
started being an issue at some point, when the DRM was changed to
adhere to the documented probe sequence: the MediaTek DSI driver was
not the only one that got broken/affected by these changes.

If you have any advice on which commit should be tagged, I'm open for
any kind of suggestion.


I tried to check on other drivers which got fixed for the same behavior,
for example drm/msm, but none of them had a Fixes tag.
When the DRM got changed to adhere to this sequence, some drm/bridge
drivers were also changed; this has created some incompatibilities with
some drm drivers, including drm/msm and drm/mediatek.

This commit is not fixing a latent bug that was introduced in drm/mediatek
but rather one that was induced by the new, fixed, probe flow that got
recently documented - and to which drivers should adhere; failing to adhere
to that will produce an endless -EPROBE_DEFER loop, due to other drivers
(as mentioned, for example drm/bridge drivers) having been changed to use
that probe sequence.


Regards,
Angelo

Regards,
Chun-Kuang.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
Reviewed-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
Reviewed-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>

---
  drivers/gpu/drm/mediatek/mtk_dsi.c | 167 +++++++++++++++--------------
  1 file changed, 84 insertions(+), 83 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
index 5d90d2eb0019..bced4c7d668e 100644
--- a/drivers/gpu/drm/mediatek/mtk_dsi.c
+++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
@@ -786,18 +786,101 @@ void mtk_dsi_ddp_stop(struct device *dev)
         mtk_dsi_poweroff(dsi);
  }

+static int mtk_dsi_encoder_init(struct drm_device *drm, struct mtk_dsi *dsi)
+{
+       int ret;
+
+       ret = drm_simple_encoder_init(drm, &dsi->encoder,
+                                     DRM_MODE_ENCODER_DSI);
+       if (ret) {
+               DRM_ERROR("Failed to encoder init to drm\n");
+               return ret;
+       }
+
+       dsi->encoder.possible_crtcs = mtk_drm_find_possible_crtc_by_comp(drm, dsi->host.dev);
+
+       ret = drm_bridge_attach(&dsi->encoder, &dsi->bridge, NULL,
+                               DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+       if (ret)
+               goto err_cleanup_encoder;
+
+       dsi->connector = drm_bridge_connector_init(drm, &dsi->encoder);
+       if (IS_ERR(dsi->connector)) {
+               DRM_ERROR("Unable to create bridge connector\n");
+               ret = PTR_ERR(dsi->connector);
+               goto err_cleanup_encoder;
+       }
+       drm_connector_attach_encoder(dsi->connector, &dsi->encoder);
+
+       return 0;
+
+err_cleanup_encoder:
+       drm_encoder_cleanup(&dsi->encoder);
+       return ret;
+}
+
+static int mtk_dsi_bind(struct device *dev, struct device *master, void *data)
+{
+       int ret;
+       struct drm_device *drm = data;
+       struct mtk_dsi *dsi = dev_get_drvdata(dev);
+
+       ret = mtk_dsi_encoder_init(drm, dsi);
+       if (ret)
+               return ret;
+
+       return device_reset_optional(dev);
+}
+
+static void mtk_dsi_unbind(struct device *dev, struct device *master,
+                          void *data)
+{
+       struct mtk_dsi *dsi = dev_get_drvdata(dev);
+
+       drm_encoder_cleanup(&dsi->encoder);
+}
+
+static const struct component_ops mtk_dsi_component_ops = {
+       .bind = mtk_dsi_bind,
+       .unbind = mtk_dsi_unbind,
+};
+
  static int mtk_dsi_host_attach(struct mipi_dsi_host *host,
                                struct mipi_dsi_device *device)
  {
         struct mtk_dsi *dsi = host_to_dsi(host);
+       struct device *dev = host->dev;
+       int ret;

         dsi->lanes = device->lanes;
         dsi->format = device->format;
         dsi->mode_flags = device->mode_flags;
+       dsi->next_bridge = devm_drm_of_get_bridge(dev, dev->of_node, 0, 0);
+       if (IS_ERR(dsi->next_bridge))
+               return PTR_ERR(dsi->next_bridge);
+
+       drm_bridge_add(&dsi->bridge);
+
+       ret = component_add(host->dev, &mtk_dsi_component_ops);
+       if (ret) {
+               DRM_ERROR("failed to add dsi_host component: %d\n", ret);
+               drm_bridge_remove(&dsi->bridge);
+               return ret;
+       }

         return 0;
  }

+static int mtk_dsi_host_detach(struct mipi_dsi_host *host,
+                              struct mipi_dsi_device *device)
+{
+       struct mtk_dsi *dsi = host_to_dsi(host);
+
+       component_del(host->dev, &mtk_dsi_component_ops);
+       drm_bridge_remove(&dsi->bridge);
+       return 0;
+}
+
  static void mtk_dsi_wait_for_idle(struct mtk_dsi *dsi)
  {
         int ret;
@@ -938,73 +1021,14 @@ static ssize_t mtk_dsi_host_transfer(struct mipi_dsi_host *host,

  static const struct mipi_dsi_host_ops mtk_dsi_ops = {
         .attach = mtk_dsi_host_attach,
+       .detach = mtk_dsi_host_detach,
         .transfer = mtk_dsi_host_transfer,
  };

-static int mtk_dsi_encoder_init(struct drm_device *drm, struct mtk_dsi *dsi)
-{
-       int ret;
-
-       ret = drm_simple_encoder_init(drm, &dsi->encoder,
-                                     DRM_MODE_ENCODER_DSI);
-       if (ret) {
-               DRM_ERROR("Failed to encoder init to drm\n");
-               return ret;
-       }
-
-       dsi->encoder.possible_crtcs = mtk_drm_find_possible_crtc_by_comp(drm, dsi->host.dev);
-
-       ret = drm_bridge_attach(&dsi->encoder, &dsi->bridge, NULL,
-                               DRM_BRIDGE_ATTACH_NO_CONNECTOR);
-       if (ret)
-               goto err_cleanup_encoder;
-
-       dsi->connector = drm_bridge_connector_init(drm, &dsi->encoder);
-       if (IS_ERR(dsi->connector)) {
-               DRM_ERROR("Unable to create bridge connector\n");
-               ret = PTR_ERR(dsi->connector);
-               goto err_cleanup_encoder;
-       }
-       drm_connector_attach_encoder(dsi->connector, &dsi->encoder);
-
-       return 0;
-
-err_cleanup_encoder:
-       drm_encoder_cleanup(&dsi->encoder);
-       return ret;
-}
-
-static int mtk_dsi_bind(struct device *dev, struct device *master, void *data)
-{
-       int ret;
-       struct drm_device *drm = data;
-       struct mtk_dsi *dsi = dev_get_drvdata(dev);
-
-       ret = mtk_dsi_encoder_init(drm, dsi);
-       if (ret)
-               return ret;
-
-       return device_reset_optional(dev);
-}
-
-static void mtk_dsi_unbind(struct device *dev, struct device *master,
-                          void *data)
-{
-       struct mtk_dsi *dsi = dev_get_drvdata(dev);
-
-       drm_encoder_cleanup(&dsi->encoder);
-}
-
-static const struct component_ops mtk_dsi_component_ops = {
-       .bind = mtk_dsi_bind,
-       .unbind = mtk_dsi_unbind,
-};
-
  static int mtk_dsi_probe(struct platform_device *pdev)
  {
         struct mtk_dsi *dsi;
         struct device *dev = &pdev->dev;
-       struct drm_panel *panel;
         struct resource *regs;
         int irq_num;
         int ret;
@@ -1021,19 +1045,6 @@ static int mtk_dsi_probe(struct platform_device *pdev)
                 return ret;
         }

-       ret = drm_of_find_panel_or_bridge(dev->of_node, 0, 0,
-                                         &panel, &dsi->next_bridge);
-       if (ret)
-               goto err_unregister_host;
-
-       if (panel) {
-               dsi->next_bridge = devm_drm_panel_bridge_add(dev, panel);
-               if (IS_ERR(dsi->next_bridge)) {
-                       ret = PTR_ERR(dsi->next_bridge);
-                       goto err_unregister_host;
-               }
-       }
-
         dsi->driver_data = of_device_get_match_data(dev);

         dsi->engine_clk = devm_clk_get(dev, "engine");
@@ -1098,14 +1109,6 @@ static int mtk_dsi_probe(struct platform_device *pdev)
         dsi->bridge.of_node = dev->of_node;
         dsi->bridge.type = DRM_MODE_CONNECTOR_DSI;

-       drm_bridge_add(&dsi->bridge);
-
-       ret = component_add(&pdev->dev, &mtk_dsi_component_ops);
-       if (ret) {
-               dev_err(&pdev->dev, "failed to add component: %d\n", ret);
-               goto err_unregister_host;
-       }
-
         return 0;

  err_unregister_host:
@@ -1118,8 +1121,6 @@ static int mtk_dsi_remove(struct platform_device *pdev)
         struct mtk_dsi *dsi = platform_get_drvdata(pdev);

         mtk_output_dsi_disable(dsi);
-       drm_bridge_remove(&dsi->bridge);
-       component_del(&pdev->dev, &mtk_dsi_component_ops);
         mipi_dsi_host_unregister(&dsi->host);

         return 0;
--
2.33.1



--
AngeloGioacchino Del Regno
Software Engineer

Collabora Ltd.
Platinum Building, St John's Innovation Park, Cambridge CB4 0DS, UK
Registered in England & Wales, no. 5513718






