[PATCH v2 02/20] drm/tegra: Don't register DP AUX channels before connectors

[PATCH v2 02/20] drm/tegra: Don't register DP AUX channels before connectors

[Lyude Paul]

As pointed out by the documentation for drm_dp_aux_register(),
drm_dp_aux_init() should be used in situations where the AUX channel for a
display driver can potentially be registered before it's respective DRM
driver. This is the case with Tegra, since the DP aux channel exists as a
platform device instead of being a grandchild of the DRM device.

Since we're about to add a backpointer to a DP AUX channel's respective DRM
device, let's fix this so that we don't potentially allow userspace to use
the AUX channel before we've associated it with it's DRM connector.

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
 drivers/gpu/drm/tegra/dpaux.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/tegra/dpaux.c b/drivers/gpu/drm/tegra/dpaux.c
index 105fb9cdbb3b..ea56c6ec25e4 100644
--- a/drivers/gpu/drm/tegra/dpaux.c
+++ b/drivers/gpu/drm/tegra/dpaux.c
@@ -534,9 +534,7 @@ static int tegra_dpaux_probe(struct platform_device *pdev)
 	dpaux->aux.transfer = tegra_dpaux_transfer;
 	dpaux->aux.dev = &pdev->dev;
 
-	err = drm_dp_aux_register(&dpaux->aux);
-	if (err < 0)
-		return err;
+	drm_dp_aux_init(&dpaux->aux);
 
 	/*
 	 * Assume that by default the DPAUX/I2C pads will be used for HDMI,
@@ -589,8 +587,6 @@ static int tegra_dpaux_remove(struct platform_device *pdev)
 	pm_runtime_put_sync(&pdev->dev);
 	pm_runtime_disable(&pdev->dev);
 
-	drm_dp_aux_unregister(&dpaux->aux);
-
 	mutex_lock(&dpaux_lock);
 	list_del(&dpaux->list);
 	mutex_unlock(&dpaux_lock);
@@ -723,6 +719,10 @@ int drm_dp_aux_attach(struct drm_dp_aux *aux, struct tegra_output *output)
 	unsigned long timeout;
 	int err;
 
+	err = drm_dp_aux_register(aux);
+	if (err < 0)
+		return err;
+
 	output->connector.polled = DRM_CONNECTOR_POLL_HPD;
 	dpaux->output = output;
 
@@ -760,6 +760,7 @@ int drm_dp_aux_detach(struct drm_dp_aux *aux)
 	unsigned long timeout;
 	int err;
 
+	drm_dp_aux_unregister(aux);
 	disable_irq(dpaux->irq);
 
 	if (dpaux->output->panel) {
-- 
2.30.2

[PATCH v2 05/20] drm/dp: Add backpointer to drm_device in drm_dp_aux

[Lyude Paul]

This is something that we've wanted for a while now: the ability to
actually look up the respective drm_device for a given drm_dp_aux struct.
This will also allow us to transition over to using the drm_dbg_*() helpers
for debug message printing, as we'll finally have a drm_device to reference
for doing so.

Note that there is one limitation with this - because some DP AUX adapters
exist as platform devices which are initialized independently of their
respective DRM devices, one cannot rely on drm_dp_aux->drm_dev to always be
non-NULL until drm_dp_aux_register() has been called. We make sure to point
this out in the documentation for struct drm_dp_aux.

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
 drivers/gpu/drm/amd/amdgpu/atombios_dp.c                 | 1 +
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c  | 1 +
 drivers/gpu/drm/bridge/analogix/analogix-anx6345.c       | 1 +
 drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c       | 1 +
 drivers/gpu/drm/bridge/analogix/analogix_dp_core.c       | 1 +
 drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c      | 1 +
 drivers/gpu/drm/bridge/tc358767.c                        | 1 +
 drivers/gpu/drm/bridge/ti-sn65dsi86.c                    | 1 +
 drivers/gpu/drm/drm_dp_aux_dev.c                         | 6 ++++++
 drivers/gpu/drm/drm_dp_mst_topology.c                    | 1 +
 drivers/gpu/drm/i915/display/intel_dp_aux.c              | 1 +
 drivers/gpu/drm/msm/edp/edp.h                            | 3 +--
 drivers/gpu/drm/msm/edp/edp_aux.c                        | 5 +++--
 drivers/gpu/drm/msm/edp/edp_ctrl.c                       | 2 +-
 drivers/gpu/drm/nouveau/nouveau_connector.c              | 1 +
 drivers/gpu/drm/radeon/atombios_dp.c                     | 1 +
 drivers/gpu/drm/tegra/dpaux.c                            | 1 +
 drivers/gpu/drm/xlnx/zynqmp_dp.c                         | 1 +
 include/drm/drm_dp_helper.h                              | 9 ++++++++-
 19 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/atombios_dp.c b/drivers/gpu/drm/amd/amdgpu/atombios_dp.c
index a3ba9ca11e98..6d35da65e09f 100644
--- a/drivers/gpu/drm/amd/amdgpu/atombios_dp.c
+++ b/drivers/gpu/drm/amd/amdgpu/atombios_dp.c
@@ -188,6 +188,7 @@ void amdgpu_atombios_dp_aux_init(struct amdgpu_connector *amdgpu_connector)
 {
 	amdgpu_connector->ddc_bus->rec.hpd = amdgpu_connector->hpd.hpd;
 	amdgpu_connector->ddc_bus->aux.transfer = amdgpu_atombios_dp_aux_transfer;
+	amdgpu_connector->ddc_bus->aux.drm_dev = amdgpu_connector->base.dev;
 	drm_dp_aux_init(&amdgpu_connector->ddc_bus->aux);
 	amdgpu_connector->ddc_bus->has_aux = true;
 }
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
index 73cdb9fe981a..b8b69c33fb2b 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -434,6 +434,7 @@ void amdgpu_dm_initialize_dp_connector(struct amdgpu_display_manager *dm,
 			  link_index);
 	aconnector->dm_dp_aux.aux.transfer = dm_dp_aux_transfer;
 	aconnector->dm_dp_aux.ddc_service = aconnector->dc_link->ddc;
+	aconnector->dm_dp_aux.aux.drm_dev = dm->ddev;
 
 	drm_dp_aux_init(&aconnector->dm_dp_aux.aux);
 	drm_dp_cec_register_connector(&aconnector->dm_dp_aux.aux,
diff --git a/drivers/gpu/drm/bridge/analogix/analogix-anx6345.c b/drivers/gpu/drm/bridge/analogix/analogix-anx6345.c
index aa6cda458eb9..e33cd077595a 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix-anx6345.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix-anx6345.c
@@ -537,6 +537,7 @@ static int anx6345_bridge_attach(struct drm_bridge *bridge,
 	/* Register aux channel */
 	anx6345->aux.name = "DP-AUX";
 	anx6345->aux.dev = &anx6345->client->dev;
+	anx6345->aux.drm_dev = bridge->dev;
 	anx6345->aux.transfer = anx6345_aux_transfer;
 
 	err = drm_dp_aux_register(&anx6345->aux);
diff --git a/drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c b/drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c
index f20558618220..5e6a0ed39199 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c
@@ -905,6 +905,7 @@ static int anx78xx_bridge_attach(struct drm_bridge *bridge,
 	/* Register aux channel */
 	anx78xx->aux.name = "DP-AUX";
 	anx78xx->aux.dev = &anx78xx->client->dev;
+	anx78xx->aux.drm_dev = bridge->dev;
 	anx78xx->aux.transfer = anx78xx_aux_transfer;
 
 	err = drm_dp_aux_register(&anx78xx->aux);
diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index f115233b1cb9..550814ca2139 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -1765,6 +1765,7 @@ int analogix_dp_bind(struct analogix_dp_device *dp, struct drm_device *drm_dev)
 	dp->aux.name = "DP-AUX";
 	dp->aux.transfer = analogix_dpaux_transfer;
 	dp->aux.dev = dp->dev;
+	dp->aux.drm_dev = drm_dev;
 
 	ret = drm_dp_aux_register(&dp->aux);
 	if (ret)
diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
index d966a33743b5..fe821ad628ec 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
@@ -1674,6 +1674,7 @@ static int cdns_mhdp_attach(struct drm_bridge *bridge,
 
 	dev_dbg(mhdp->dev, "%s\n", __func__);
 
+	mhdp->aux.drm_dev = bridge->dev;
 	ret = drm_dp_aux_register(&mhdp->aux);
 	if (ret < 0)
 		return ret;
diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
index da89922721ed..23a6f90b694b 100644
--- a/drivers/gpu/drm/bridge/tc358767.c
+++ b/drivers/gpu/drm/bridge/tc358767.c
@@ -1414,6 +1414,7 @@ static int tc_bridge_attach(struct drm_bridge *bridge,
 	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
 		return 0;
 
+	tc->aux.drm_dev = drm;
 	ret = drm_dp_aux_register(&tc->aux);
 	if (ret < 0)
 		return ret;
diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 88df4dd0f39d..8e24272bbf00 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -362,6 +362,7 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge,
 		return -EINVAL;
 	}
 
+	pdata->aux.drm_dev = bridge->dev;
 	ret = drm_dp_aux_register(&pdata->aux);
 	if (ret < 0) {
 		drm_err(bridge->dev, "Failed to register DP AUX channel: %d\n", ret);
diff --git a/drivers/gpu/drm/drm_dp_aux_dev.c b/drivers/gpu/drm/drm_dp_aux_dev.c
index e25181bf2c48..06b374cae956 100644
--- a/drivers/gpu/drm/drm_dp_aux_dev.c
+++ b/drivers/gpu/drm/drm_dp_aux_dev.c
@@ -278,6 +278,12 @@ void drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux)
 	if (!aux_dev) /* attach must have failed */
 		return;
 
+	/*
+	 * As some AUX adapters may exist as platform devices which outlive their respective DRM
+	 * devices, we clear drm_dev to ensure that we never accidentally reference a stale pointer
+	 */
+	aux->drm_dev = NULL;
+
 	mutex_lock(&aux_idr_mutex);
 	idr_remove(&aux_idr, aux_dev->index);
 	mutex_unlock(&aux_idr_mutex);
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 42a0c6888c33..1a7a8b085de4 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2350,6 +2350,7 @@ drm_dp_mst_add_port(struct drm_device *dev,
 	port->aux.is_remote = true;
 
 	/* initialize the MST downstream port's AUX crc work queue */
+	port->aux.drm_dev = dev;
 	drm_dp_remote_aux_init(&port->aux);
 
 	/*
diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
index 7e83bc2cc34a..c4b446d6a042 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
@@ -682,6 +682,7 @@ void intel_dp_aux_init(struct intel_dp *intel_dp)
 	else
 		intel_dp->get_aux_send_ctl = g4x_get_aux_send_ctl;
 
+	intel_dp->aux.drm_dev = &dev_priv->drm;
 	drm_dp_aux_init(&intel_dp->aux);
 
 	/* Failure to allocate our preferred name is not critical */
diff --git a/drivers/gpu/drm/msm/edp/edp.h b/drivers/gpu/drm/msm/edp/edp.h
index eb34243dad53..8590f2ce274d 100644
--- a/drivers/gpu/drm/msm/edp/edp.h
+++ b/drivers/gpu/drm/msm/edp/edp.h
@@ -46,8 +46,7 @@ void edp_bridge_destroy(struct drm_bridge *bridge);
 struct drm_connector *msm_edp_connector_init(struct msm_edp *edp);
 
 /* AUX */
-void *msm_edp_aux_init(struct device *dev, void __iomem *regbase,
-			struct drm_dp_aux **drm_aux);
+void *msm_edp_aux_init(struct msm_edp *edp, void __iomem *regbase, struct drm_dp_aux **drm_aux);
 void msm_edp_aux_destroy(struct device *dev, struct edp_aux *aux);
 irqreturn_t msm_edp_aux_irq(struct edp_aux *aux, u32 isr);
 void msm_edp_aux_ctrl(struct edp_aux *aux, int enable);
diff --git a/drivers/gpu/drm/msm/edp/edp_aux.c b/drivers/gpu/drm/msm/edp/edp_aux.c
index df10a0196d94..e3d85c622cfb 100644
--- a/drivers/gpu/drm/msm/edp/edp_aux.c
+++ b/drivers/gpu/drm/msm/edp/edp_aux.c
@@ -184,9 +184,9 @@ static ssize_t edp_aux_transfer(struct drm_dp_aux *drm_aux,
 	return ret;
 }
 
-void *msm_edp_aux_init(struct device *dev, void __iomem *regbase,
-	struct drm_dp_aux **drm_aux)
+void *msm_edp_aux_init(struct msm_edp *edp, void __iomem *regbase, struct drm_dp_aux **drm_aux)
 {
+	struct device *dev = &edp->pdev->dev;
 	struct edp_aux *aux = NULL;
 	int ret;
 
@@ -201,6 +201,7 @@ void *msm_edp_aux_init(struct device *dev, void __iomem *regbase,
 
 	aux->drm_aux.name = "msm_edp_aux";
 	aux->drm_aux.dev = dev;
+	aux->drm_aux.drm_dev = edp->dev;
 	aux->drm_aux.transfer = edp_aux_transfer;
 	ret = drm_dp_aux_register(&aux->drm_aux);
 	if (ret) {
diff --git a/drivers/gpu/drm/msm/edp/edp_ctrl.c b/drivers/gpu/drm/msm/edp/edp_ctrl.c
index 0d9657cc70db..57af3d8b6699 100644
--- a/drivers/gpu/drm/msm/edp/edp_ctrl.c
+++ b/drivers/gpu/drm/msm/edp/edp_ctrl.c
@@ -1153,7 +1153,7 @@ int msm_edp_ctrl_init(struct msm_edp *edp)
 	}
 
 	/* Init aux and phy */
-	ctrl->aux = msm_edp_aux_init(dev, ctrl->base, &ctrl->drm_aux);
+	ctrl->aux = msm_edp_aux_init(edp, ctrl->base, &ctrl->drm_aux);
 	if (!ctrl->aux || !ctrl->drm_aux) {
 		pr_err("%s:failed to init aux\n", __func__);
 		return -ENOMEM;
diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.c b/drivers/gpu/drm/nouveau/nouveau_connector.c
index bfce762adcf0..d1b49508ecb9 100644
--- a/drivers/gpu/drm/nouveau/nouveau_connector.c
+++ b/drivers/gpu/drm/nouveau/nouveau_connector.c
@@ -1355,6 +1355,7 @@ nouveau_connector_create(struct drm_device *dev,
 	case DRM_MODE_CONNECTOR_DisplayPort:
 	case DRM_MODE_CONNECTOR_eDP:
 		nv_connector->aux.dev = connector->kdev;
+		nv_connector->aux.drm_dev = dev;
 		nv_connector->aux.transfer = nouveau_connector_aux_xfer;
 		snprintf(aux_name, sizeof(aux_name), "sor-%04x-%04x",
 			 dcbe->hasht, dcbe->hashm);
diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
index 15b00a347560..c50c504bad50 100644
--- a/drivers/gpu/drm/radeon/atombios_dp.c
+++ b/drivers/gpu/drm/radeon/atombios_dp.c
@@ -232,6 +232,7 @@ void radeon_dp_aux_init(struct radeon_connector *radeon_connector)
 
 	radeon_connector->ddc_bus->rec.hpd = radeon_connector->hpd.hpd;
 	radeon_connector->ddc_bus->aux.dev = radeon_connector->base.kdev;
+	radeon_connector->ddc_bus->aux.drm_dev = radeon_connector->base.dev;
 	if (ASIC_IS_DCE5(rdev)) {
 		if (radeon_auxch)
 			radeon_connector->ddc_bus->aux.transfer = radeon_dp_aux_transfer_native;
diff --git a/drivers/gpu/drm/tegra/dpaux.c b/drivers/gpu/drm/tegra/dpaux.c
index ea56c6ec25e4..7d7cc90b6fc9 100644
--- a/drivers/gpu/drm/tegra/dpaux.c
+++ b/drivers/gpu/drm/tegra/dpaux.c
@@ -719,6 +719,7 @@ int drm_dp_aux_attach(struct drm_dp_aux *aux, struct tegra_output *output)
 	unsigned long timeout;
 	int err;
 
+	aux->drm_dev = output->connector.dev;
 	err = drm_dp_aux_register(aux);
 	if (err < 0)
 		return err;
diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
index 99158ee67d02..8272eee03adc 100644
--- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
+++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
@@ -1069,6 +1069,7 @@ static int zynqmp_dp_aux_init(struct zynqmp_dp *dp)
 
 	dp->aux.name = "ZynqMP DP AUX";
 	dp->aux.dev = dp->dev;
+	dp->aux.drm_dev = dp->drm;
 	dp->aux.transfer = zynqmp_dp_aux_transfer;
 
 	return drm_dp_aux_register(&dp->aux);
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 5efa0d329b67..4abe0cea1302 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1838,6 +1838,8 @@ struct drm_dp_aux_cec {
  * @name: user-visible name of this AUX channel and the I2C-over-AUX adapter
  * @ddc: I2C adapter that can be used for I2C-over-AUX communication
  * @dev: pointer to struct device that is the parent for this AUX channel
+ * @drm_dev: pointer to the &drm_device that owns this AUX channel. Beware, this may be %NULL
+ * before drm_dp_aux_register() has been called.
  * @crtc: backpointer to the crtc that is currently using this AUX channel
  * @hw_mutex: internal mutex used for locking transfers
  * @crc_work: worker that captures CRCs for each frame
@@ -1845,7 +1847,11 @@ struct drm_dp_aux_cec {
  * @transfer: transfers a message representing a single AUX transaction
  *
  * The @dev field should be set to a pointer to the device that implements the
- * AUX channel.
+ * AUX channel. As well, the @drm_dev field should be set to the &drm_device
+ * that will be using this AUX channel as early as possible. For many graphics
+ * drivers this should happen before drm_dp_aux_init(), however it's perfectly
+ * fine to set this field later so long as it's assigned before calling
+ * drm_dp_aux_register().
  *
  * The @name field may be used to specify the name of the I2C adapter. If set to
  * %NULL, dev_name() of @dev will be used.
@@ -1877,6 +1883,7 @@ struct drm_dp_aux {
 	const char *name;
 	struct i2c_adapter ddc;
 	struct device *dev;
+	struct drm_device *drm_dev;
 	struct drm_crtc *crtc;
 	struct mutex hw_mutex;
 	struct work_struct crc_work;
-- 
2.30.2

Re: [PATCH v2 02/20] drm/tegra: Don't register DP AUX channels before connectors

[Thierry Reding]

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On Fri, Mar 26, 2021 at 04:37:49PM -0400, Lyude Paul wrote:
> As pointed out by the documentation for drm_dp_aux_register(),
> drm_dp_aux_init() should be used in situations where the AUX channel for a
> display driver can potentially be registered before it's respective DRM
> driver. This is the case with Tegra, since the DP aux channel exists as a
> platform device instead of being a grandchild of the DRM device.
> 
> Since we're about to add a backpointer to a DP AUX channel's respective DRM
> device, let's fix this so that we don't potentially allow userspace to use
> the AUX channel before we've associated it with it's DRM connector.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> ---
>  drivers/gpu/drm/tegra/dpaux.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)

Acked-by: Thierry Reding <treding@nvidia.com>

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Re: [PATCH v2 05/20] drm/dp: Add backpointer to drm_device in drm_dp_aux

[Thierry Reding]

[-- Attachment #1: Type: text/plain, Size: 943 bytes --]

On Fri, Mar 26, 2021 at 04:37:52PM -0400, Lyude Paul wrote:
> This is something that we've wanted for a while now: the ability to
> actually look up the respective drm_device for a given drm_dp_aux struct.
> This will also allow us to transition over to using the drm_dbg_*() helpers
> for debug message printing, as we'll finally have a drm_device to reference
> for doing so.
> 
> Note that there is one limitation with this - because some DP AUX adapters
> exist as platform devices which are initialized independently of their
> respective DRM devices, one cannot rely on drm_dp_aux->drm_dev to always be
> non-NULL until drm_dp_aux_register() has been called. We make sure to point
> this out in the documentation for struct drm_dp_aux.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> ---
[...]
>  drivers/gpu/drm/tegra/dpaux.c                            | 1 +
[...]

Acked-by: Thierry Reding <treding@nvidia.com>

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Re: [PATCH v2 05/20] drm/dp: Add backpointer to drm_device in drm_dp_aux

[Jani Nikula]

On Fri, 26 Mar 2021, Lyude Paul <lyude@redhat.com> wrote:
>   * The @dev field should be set to a pointer to the device that implements the
> - * AUX channel.
> + * AUX channel. As well, the @drm_dev field should be set to the &drm_device
> + * that will be using this AUX channel as early as possible. For many graphics
> + * drivers this should happen before drm_dp_aux_init(), however it's perfectly
> + * fine to set this field later so long as it's assigned before calling
> + * drm_dp_aux_register().

Perhaps add a follow-up patch to actually ensure this is the case in
drm_dp_aux_register()?

>   *
>   * The @name field may be used to specify the name of the I2C adapter. If set to
>   * %NULL, dev_name() of @dev will be used.
> @@ -1877,6 +1883,7 @@ struct drm_dp_aux {
>  	const char *name;
>  	struct i2c_adapter ddc;
>  	struct device *dev;
> +	struct drm_device *drm_dev;

Bikeshed, I would probably have called it just drm for brevity, but no
strong feelings.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center