drm/client: Send hotplug event after registering a client

Generate a hotplug event after registering a client to allow the
client to configure its display. Remove the hotplug calls from the
existing clients for fbdev emulation. This change fixes a concurrency
bug between registering a client and receiving events from the DRM
core. The bug is present in the fbdev emulation of all drivers.

The fbdev emulation currently generates a hotplug event before
registering the client to the device. For each new output, the DRM
core sends an additional hotplug event to each registered client.

If the DRM core detects first output between sending the artificial
hotplug and registering the device, the output's hotplug event gets
lost. If this is the first output, the fbdev console display remains
dark. This has been observed with amdgpu and fbdev-generic.

Fix this by adding hotplug generation directly to the client's
register helper drm_client_register(). Registering the client and
receiving events are serialized by struct drm_device.clientlist_mutex.
So an output is either configured by the initial hotplug event, or
the client has already been registered.

The bug was originally added in commit 6e3f17e ("drm/fb-helper:
generic: Call drm_client_add() after setup is done"), in which adding
a client and receiving a hotplug event switched order. It was hidden,
as most hardware and drivers have at least on static output configured.
Other drivers didn't use the internal DRM client or still had struct
drm_mode_config_funcs.output_poll_changed set. That callback handled
hotplug events as well. After not setting the callback in amdgpu in
commit 0e3172b ("drm/amdgpu: Don't set struct
drm_driver.output_poll_changed"), amdgpu did not show a framebuffer
console if output events got lost. The bug got copy-pasted from
fbdev-generic into the other fbdev emulation.

Reported-by: Moritz Duge <MoritzDuge@kolahilft.de>
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/2649
Fixes: 6e3f17e ("drm/fb-helper: generic: Call drm_client_add() after setup is done")
Fixes: 8ab59da ("drm/fb-helper: Move generic fbdev emulation into separate source file")
Fixes: b79fe9a ("drm/fbdev-dma: Implement fbdev emulation for GEM DMA helpers")
Fixes: 63c3815 ("drm/armada: Implement fbdev emulation as in-kernel client")
Fixes: 49953b7 ("drm/exynos: Implement fbdev emulation as in-kernel client")
Fixes: 8f1aacc ("drm/gma500: Implement client-based fbdev emulation")
Fixes: 940b869 ("drm/msm: Implement fbdev emulation as in-kernel client")
Fixes: 9e69bcd ("drm/omapdrm: Implement fbdev emulation as in-kernel client")
Fixes: e317a69 ("drm/radeon: Implement client-based fbdev emulation")
Fixes: 71ec16f ("drm/tegra: Implement fbdev emulation as in-kernel client")
Fixes: 0e3172b ("drm/amdgpu: Don't set struct drm_driver.output_poll_changed")
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Moritz Duge <MoritzDuge@kolahilft.de>
Tested-by: Torsten Krah <krah.tm@gmail.com>
Tested-by: Paul Schyska <pschyska@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@gmail.com>
Cc: Noralf Trønnes <noralf@tronnes.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Seung-Woo Kim <sw0312.kim@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Abhinav Kumar <quic_abhinavk@quicinc.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Mikko Perttunen <mperttunen@nvidia.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
Cc: linux-arm-msm@vger.kernel.org
Cc: freedreno@lists.freedesktop.org
Cc: amd-gfx@lists.freedesktop.org
Cc: linux-tegra@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v5.2+
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> # msm
Link: https://patchwork.freedesktop.org/patch/msgid/20230710091029.27503-1-tzimmermann@suse.de

Author: Thomas Zimmermann

drivers/gpu/drm/armada/armada_fbdev.c

@@ -209,10 +209,6 @@ void armada_fbdev_setup(struct drm_device *dev)
 		goto err_drm_client_init;
 	}
 
-	ret = armada_fbdev_client_hotplug(&fbh->client);
-	if (ret)
-		drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
-
 	drm_client_register(&fbh->client);
 
 	return;

drivers/gpu/drm/drm_client.c

@@ -122,13 +122,34 @@ EXPORT_SYMBOL(drm_client_init);
  * drm_client_register() it is no longer permissible to call drm_client_release()
  * directly (outside the unregister callback), instead cleanup will happen
  * automatically on driver unload.
+ *
+ * Registering a client generates a hotplug event that allows the client
+ * to set up its display from pre-existing outputs. The client must have
+ * initialized its state to able to handle the hotplug event successfully.
  */
 void drm_client_register(struct drm_client_dev *client)
 {
 	struct drm_device *dev = client->dev;
+	int ret;
 
 	mutex_lock(&dev->clientlist_mutex);
 	list_add(&client->list, &dev->clientlist);
+
+	if (client->funcs && client->funcs->hotplug) {
+		/*
+		 * Perform an initial hotplug event to pick up the
+		 * display configuration for the client. This step
+		 * has to be performed *after* registering the client
+		 * in the list of clients, or a concurrent hotplug
+		 * event might be lost; leaving the display off.
+		 *
+		 * Hold the clientlist_mutex as for a regular hotplug
+		 * event.
+		 */
+		ret = client->funcs->hotplug(client);
+		if (ret)
+			drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
+	}
 	mutex_unlock(&dev->clientlist_mutex);
 }
 EXPORT_SYMBOL(drm_client_register);

drivers/gpu/drm/drm_fbdev_dma.c

@@ -252,10 +252,6 @@ void drm_fbdev_dma_setup(struct drm_device *dev, unsigned int preferred_bpp)
 		goto err_drm_client_init;
 	}
 
-	ret = drm_fbdev_dma_client_hotplug(&fb_helper->client);
-	if (ret)
-		drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
-
 	drm_client_register(&fb_helper->client);
 
 	return;

drivers/gpu/drm/drm_fbdev_generic.c

@@ -339,10 +339,6 @@ void drm_fbdev_generic_setup(struct drm_device *dev, unsigned int preferred_bpp)
 		goto err_drm_client_init;
 	}
 
-	ret = drm_fbdev_generic_client_hotplug(&fb_helper->client);
-	if (ret)
-		drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
-
 	drm_client_register(&fb_helper->client);
 
 	return;

drivers/gpu/drm/exynos/exynos_drm_fbdev.c

@@ -215,10 +215,6 @@ void exynos_drm_fbdev_setup(struct drm_device *dev)
 	if (ret)
 		goto err_drm_client_init;
 
-	ret = exynos_drm_fbdev_client_hotplug(&fb_helper->client);
-	if (ret)
-		drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
-
 	drm_client_register(&fb_helper->client);
 
 	return;

drivers/gpu/drm/gma500/fbdev.c

@@ -328,10 +328,6 @@ void psb_fbdev_setup(struct drm_psb_private *dev_priv)
 		goto err_drm_fb_helper_unprepare;
 	}
 
-	ret = psb_fbdev_client_hotplug(&fb_helper->client);
-	if (ret)
-		drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
-
 	drm_client_register(&fb_helper->client);
 
 	return;

drivers/gpu/drm/msm/msm_fbdev.c

@@ -246,10 +246,6 @@ void msm_fbdev_setup(struct drm_device *dev)
 		goto err_drm_fb_helper_unprepare;
 	}
 
-	ret = msm_fbdev_client_hotplug(&helper->client);
-	if (ret)
-		drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
-
 	drm_client_register(&helper->client);
 
 	return;

drivers/gpu/drm/omapdrm/omap_fbdev.c

@@ -318,10 +318,6 @@ void omap_fbdev_setup(struct drm_device *dev)
 
 	INIT_WORK(&fbdev->work, pan_worker);
 
-	ret = omap_fbdev_client_hotplug(&helper->client);
-	if (ret)
-		drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
-
 	drm_client_register(&helper->client);
 
 	return;

drivers/gpu/drm/radeon/radeon_fbdev.c

@@ -383,10 +383,6 @@ void radeon_fbdev_setup(struct radeon_device *rdev)
 		goto err_drm_client_init;
 	}
 
-	ret = radeon_fbdev_client_hotplug(&fb_helper->client);
-	if (ret)
-		drm_dbg_kms(rdev->ddev, "client hotplug ret=%d\n", ret);
-
 	drm_client_register(&fb_helper->client);
 
 	return;

drivers/gpu/drm/tegra/fbdev.c

@@ -225,10 +225,6 @@ void tegra_fbdev_setup(struct drm_device *dev)
 	if (ret)
 		goto err_drm_client_init;
 
-	ret = tegra_fbdev_client_hotplug(&helper->client);
-	if (ret)
-		drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
-
 	drm_client_register(&helper->client);
 
 	return;