Nouveau - Nov 2018 - [PATCH 2/2] drm/nouveau: Grab an rpm reference before/after DP AUX transactions

Here's some fixes for the less important DP AUX issues I mentioned a
while back.

Lyude Paul (2):
  drm/dp: Add ->pre/post_transfer() hooks for drm_dp_aux
  drm/nouveau: Grab an rpm reference before/after DP AUX transactions

 drivers/gpu/drm/drm_dp_helper.c             |  5 ++
 drivers/gpu/drm/nouveau/nouveau_connector.c | 36 ++++++++
 drivers/gpu/drm/nouveau/nouveau_drm.c       | 12 ++-
 drivers/gpu/drm/nouveau/nouveau_drv.h       |  8 ++
 include/drm/drm_dp_helper.h                 | 91 +++++++++++++++++++++
 5 files changed, 151 insertions(+), 1 deletion(-)

-- 
2.19.1

Many DRM drivers unfortunately need to be able to access the DP AUX
channel during their suspend/resume callbacks. This leads to an annoying
catch-22: drivers which try to ensure that the DP AUX channel is
initialized and ready may need to runtime-resume the device housing the
channel, which would lead to a deadlock between runtime power management
and drm_dp_aux->hw_mutex.

So: add a simple set of optional hooks that drivers can implement in
order to perform such setup before hw_mutex is locked, then clean up
afterwards. We additionally add the drm_dp_aux_get() and
drm_dp_aux_put() functions so that users of the AUX channel that need to
prepare the AUX channel ahead of time to avoid other kinds of locking
version can do so. We'll need this if we ever want to have a universal
dp_mst_status debugfs node, since dumping the MST topology without
having the AUX channel prepared beforehand would lead to lock inversion.

Signed-off-by: Lyude Paul <lyude at redhat.com>
---
 drivers/gpu/drm/drm_dp_helper.c |  5 ++
 include/drm/drm_dp_helper.h     | 91 +++++++++++++++++++++++++++++++++
 2 files changed, 96 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 6d483487f2b4..fb1912a2f246 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -224,6 +224,10 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8
request,
 	msg.buffer = buffer;
 	msg.size = size;
 
+	ret = drm_dp_aux_get(aux);
+	if (ret)
+		return ret;
+
 	mutex_lock(&aux->hw_mutex);
 
 	/*
@@ -265,6 +269,7 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8
request,
 
 unlock:
 	mutex_unlock(&aux->hw_mutex);
+	drm_dp_aux_put(aux);
 	return ret;
 }
 
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 3314e91f6eb3..b0208bc666d1 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1243,6 +1243,46 @@ struct drm_dp_aux {
 	struct mutex hw_mutex;
 	struct work_struct crc_work;
 	u8 crc_count;
+	/**
+	 * @pre_transfer:
+	 *
+	 * An optional callback for drivers that if implemented, will be
+	 * called before locking @hw_mutex and beginning a DP AUX transaction.
+	 *
+	 * Drivers can use this to perform any initialization that might be
+	 * required before the DP AUX channel is ready to be used, such as
+	 * waking up the device housing the AUX channel.
+	 *
+	 * This callback may be called more then once for a single
+	 * transaction.
+	 *
+	 * See also:
+	 * drm_dp_aux_get()
+	 * drm_dp_aux_put()
+	 *
+	 * Returns:
+	 *
+	 * 0 on success, negative error code on failure.
+	 */
+	int (*pre_transfer)(struct drm_dp_aux *aux);
+	/**
+	 * @post_transfer:
+	 *
+	 * An optional callback for drivers that if implemented, will be
+	 * called after having performed a DP AUX transaction.
+	 *
+	 * Drivers can use this to undo any initialization that was performed
+	 * by @pre_transfer, such as putting the device housing the DP AUX
+	 * channel back to sleep.
+	 *
+	 * This callback may be called more then once for a single
+	 * transaction.
+	 *
+	 * See also:
+	 * drm_dp_aux_get()
+	 * drm_dp_aux_put()
+	 */
+	void (*post_transfer)(struct drm_dp_aux *aux);
 	ssize_t (*transfer)(struct drm_dp_aux *aux,
 			    struct drm_dp_aux_msg *msg);
 	/**
@@ -1259,6 +1299,57 @@ struct drm_dp_aux {
 	struct drm_dp_aux_cec cec;
 };
 
+/**
+ * drm_dp_aux_get() - Prepare a DP AUX channel for a transaction
+ * @aux: DisplayPort AUX channel to initialize
+ *
+ * If implemented by the driver, this function will invoke the
+ * &drm_dp_aux.pre_transfer callback for the given @aux device. This
function
+ * can be used to setup the DP AUX channel before going under lock, in order
+ * to avoid lock inversion between the DP AUX channel setup and
+ * &drm_dp_aux.hw_mutex. This function is implicitly called by
+ * drm_dp_dpcd_read(), drm_dp_dpcd_readb(), drm_dp_dpcd_write(), and
+ * drm_dp_dpcd_writeb().
+ *
+ * Each call to drm_dp_aux_get() must have a matching drm_dp_aux_put() call to
+ * cleanup any resources that were required for the DP AUX transaction.
+ *
+ * See also:
+ * drm_dp_aux_put()
+ *
+ * Returns:
+ * 0 on success, negative error code on failure
+ */
+static inline int drm_dp_aux_get(struct drm_dp_aux *aux)
+{
+	if (aux->pre_transfer)
+		return aux->pre_transfer(aux);
+	else
+		return 0;
+}
+
+/**
+ * drm_dp_aux_put() - Cleanup after performing a transaction on a DP AUX
+ * channel
+ * @aux: DisplayPort AUX channel to cleanup
+ *
+ * If implemented by the driver, this function will invoke the
+ * &drm_dp_aux.post_transfer callback for the given @aux device. This
function
+ * is implicitly called by drm_dp_dpcd_read(), drm_dp_dpcd_readb(),
+ * drm_dp_dpcd_write(), and drm_dp_dpcd_writeb().
+ *
+ * Each call to drm_dp_aux_get() must have a matching drm_dp_aux_put() call to
+ * cleanup any resources that were required for the DP AUX transaction.
+ *
+ * See also:
+ * drm_dp_aux_get()
+ */
+static inline void drm_dp_aux_put(struct drm_dp_aux *aux)
+{
+	if (aux->post_transfer)
+		aux->post_transfer(aux);
+}
+
 ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
 			 void *buffer, size_t size);
 ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
-- 
2.19.1

Now that we have ->pre_transfer() and ->post_transfer() for DP AUX
channel devices, we can implement these hooks in order to ensure that
the GPU is actually woken up before AUX transactions happen. This fixes
/dev/drm_dp_aux* not working while the GPU is suspended, along with some
more rare issues where the GPU might runtime-suspend if the time between
two DP AUX channel transactions ends up being longer then the runtime
suspend delay (sometimes observed on KASAN kernels where everything is
slow).

Additionally, we add tracking for the current task that's running our
runtime suspend/resume callbacks. We need this in order to avoid trying
to grab a runtime power reference when nouveau uses the DP AUX channel
for MST suspend/resume in it's runtime susped/resume callbacks.

Signed-off-by: Lyude Paul <lyude at redhat.com>
---
 drivers/gpu/drm/nouveau/nouveau_connector.c | 36 +++++++++++++++++++++
 drivers/gpu/drm/nouveau/nouveau_drm.c       | 12 ++++++-
 drivers/gpu/drm/nouveau/nouveau_drv.h       |  8 +++++
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.c
b/drivers/gpu/drm/nouveau/nouveau_connector.c
index fd80661dff92..d2e9752f2f91 100644
--- a/drivers/gpu/drm/nouveau/nouveau_connector.c
+++ b/drivers/gpu/drm/nouveau/nouveau_connector.c
@@ -1171,6 +1171,38 @@ nouveau_connector_hotplug(struct nvif_notify *notify)
 	return NVIF_NOTIFY_KEEP;
 }
 
+static int
+nouveau_connector_aux_pre_xfer(struct drm_dp_aux *obj)
+{
+	struct nouveau_connector *nv_connector +		container_of(obj,
typeof(*nv_connector), aux);
+	struct nouveau_drm *drm = nouveau_drm(nv_connector->base.dev);
+	int ret;
+
+	if (nouveau_is_rpm_worker(drm))
+		return 0;
+
+	ret = pm_runtime_get_sync(drm->dev->dev);
+	if (ret < 0 && ret != -EAGAIN)
+		return ret;
+
+	return 0;
+}
+
+static void
+nouveau_connector_aux_post_xfer(struct drm_dp_aux *obj)
+{
+	struct nouveau_connector *nv_connector +		container_of(obj,
typeof(*nv_connector), aux);
+	struct nouveau_drm *drm = nouveau_drm(nv_connector->base.dev);
+
+	if (nouveau_is_rpm_worker(drm))
+		return;
+
+	pm_runtime_mark_last_busy(drm->dev->dev);
+	pm_runtime_put_autosuspend(drm->dev->dev);
+}
+
 static ssize_t
 nouveau_connector_aux_xfer(struct drm_dp_aux *obj, struct drm_dp_aux_msg *msg)
 {
@@ -1341,6 +1373,10 @@ nouveau_connector_create(struct drm_device *dev, int
index)
 	case DRM_MODE_CONNECTOR_DisplayPort:
 	case DRM_MODE_CONNECTOR_eDP:
 		nv_connector->aux.dev = dev->dev;
+		nv_connector->aux.pre_transfer +			nouveau_connector_aux_pre_xfer;
+		nv_connector->aux.post_transfer +			nouveau_connector_aux_post_xfer;
 		nv_connector->aux.transfer = nouveau_connector_aux_xfer;
 		ret = drm_dp_aux_register(&nv_connector->aux);
 		if (ret) {
diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c
b/drivers/gpu/drm/nouveau/nouveau_drm.c
index 2b2baf6e0e0d..4323e9e61c2e 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
@@ -859,6 +859,7 @@ nouveau_pmops_runtime_suspend(struct device *dev)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct drm_device *drm_dev = pci_get_drvdata(pdev);
+	struct nouveau_drm *drm = nouveau_drm(drm_dev);
 	int ret;
 
 	if (!nouveau_pmops_runtime()) {
@@ -866,6 +867,8 @@ nouveau_pmops_runtime_suspend(struct device *dev)
 		return -EBUSY;
 	}
 
+	drm->rpm_task = current;
+
 	nouveau_switcheroo_optimus_dsm();
 	ret = nouveau_do_suspend(drm_dev, true);
 	pci_save_state(pdev);
@@ -873,6 +876,8 @@ nouveau_pmops_runtime_suspend(struct device *dev)
 	pci_ignore_hotplug(pdev);
 	pci_set_power_state(pdev, PCI_D3cold);
 	drm_dev->switch_power_state = DRM_SWITCH_POWER_DYNAMIC_OFF;
+
+	drm->rpm_task = NULL;
 	return ret;
 }
 
@@ -881,6 +886,7 @@ nouveau_pmops_runtime_resume(struct device *dev)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct drm_device *drm_dev = pci_get_drvdata(pdev);
+	struct nouveau_drm *drm = nouveau_drm(drm_dev);
 	struct nvif_device *device = &nouveau_drm(drm_dev)->client.device;
 	int ret;
 
@@ -889,11 +895,13 @@ nouveau_pmops_runtime_resume(struct device *dev)
 		return -EBUSY;
 	}
 
+	drm->rpm_task = current;
+
 	pci_set_power_state(pdev, PCI_D0);
 	pci_restore_state(pdev);
 	ret = pci_enable_device(pdev);
 	if (ret)
-		return ret;
+		goto out;
 	pci_set_master(pdev);
 
 	ret = nouveau_do_resume(drm_dev, true);
@@ -905,6 +913,8 @@ nouveau_pmops_runtime_resume(struct device *dev)
 	/* Monitors may have been connected / disconnected during suspend */
 	schedule_work(&nouveau_drm(drm_dev)->hpd_work);
 
+out:
+	drm->rpm_task = NULL;
 	return ret;
 }
 
diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h
b/drivers/gpu/drm/nouveau/nouveau_drv.h
index 0b2191fa96f7..e8d4203ddfb4 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drv.h
+++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
@@ -212,6 +212,8 @@ struct nouveau_drm {
 	bool have_disp_power_ref;
 
 	struct dev_pm_domain vga_pm_domain;
+
+	struct task_struct *rpm_task;
 };
 
 static inline struct nouveau_drm *
@@ -231,6 +233,12 @@ int nouveau_pmops_suspend(struct device *);
 int nouveau_pmops_resume(struct device *);
 bool nouveau_pmops_runtime(void);
 
+static inline bool
+nouveau_is_rpm_worker(struct nouveau_drm *drm)
+{
+	return drm->rpm_task == current;
+}
+
 #include <nvkm/core/tegra.h>
 
 struct drm_device *
-- 
2.19.1

why the nouveau_is_rpm_worker stuff?
On Sat, Nov 17, 2018 at 2:50 AM Lyude Paul <lyude at redhat.com>
wrote:
>
> Now that we have ->pre_transfer() and ->post_transfer() for DP AUX
> channel devices, we can implement these hooks in order to ensure that
> the GPU is actually woken up before AUX transactions happen. This fixes
> /dev/drm_dp_aux* not working while the GPU is suspended, along with some
> more rare issues where the GPU might runtime-suspend if the time between
> two DP AUX channel transactions ends up being longer then the runtime
> suspend delay (sometimes observed on KASAN kernels where everything is
> slow).
>
> Additionally, we add tracking for the current task that's running our
> runtime suspend/resume callbacks. We need this in order to avoid trying
> to grab a runtime power reference when nouveau uses the DP AUX channel
> for MST suspend/resume in it's runtime susped/resume callbacks.
>
> Signed-off-by: Lyude Paul <lyude at redhat.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_connector.c | 36 +++++++++++++++++++++
>  drivers/gpu/drm/nouveau/nouveau_drm.c       | 12 ++++++-
>  drivers/gpu/drm/nouveau/nouveau_drv.h       |  8 +++++
>  3 files changed, 55 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.c
b/drivers/gpu/drm/nouveau/nouveau_connector.c
> index fd80661dff92..d2e9752f2f91 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_connector.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_connector.c
> @@ -1171,6 +1171,38 @@ nouveau_connector_hotplug(struct nvif_notify
*notify)
>         return NVIF_NOTIFY_KEEP;
>  }
>
> +static int
> +nouveau_connector_aux_pre_xfer(struct drm_dp_aux *obj)
> +{
> +       struct nouveau_connector *nv_connector > +              
container_of(obj, typeof(*nv_connector), aux);
> +       struct nouveau_drm *drm = nouveau_drm(nv_connector->base.dev);
> +       int ret;
> +
> +       if (nouveau_is_rpm_worker(drm))
> +               return 0;
> +
> +       ret = pm_runtime_get_sync(drm->dev->dev);
> +       if (ret < 0 && ret != -EAGAIN)
> +               return ret;
> +
> +       return 0;
> +}
> +
> +static void
> +nouveau_connector_aux_post_xfer(struct drm_dp_aux *obj)
> +{
> +       struct nouveau_connector *nv_connector > +              
container_of(obj, typeof(*nv_connector), aux);
> +       struct nouveau_drm *drm = nouveau_drm(nv_connector->base.dev);
> +
> +       if (nouveau_is_rpm_worker(drm))
> +               return;
> +
> +       pm_runtime_mark_last_busy(drm->dev->dev);
> +       pm_runtime_put_autosuspend(drm->dev->dev);
> +}
> +
>  static ssize_t
>  nouveau_connector_aux_xfer(struct drm_dp_aux *obj, struct drm_dp_aux_msg
*msg)
>  {
> @@ -1341,6 +1373,10 @@ nouveau_connector_create(struct drm_device *dev, int
index)
>         case DRM_MODE_CONNECTOR_DisplayPort:
>         case DRM_MODE_CONNECTOR_eDP:
>                 nv_connector->aux.dev = dev->dev;
> +               nv_connector->aux.pre_transfer > +                   
nouveau_connector_aux_pre_xfer;
> +               nv_connector->aux.post_transfer > +                  
nouveau_connector_aux_post_xfer;
>                 nv_connector->aux.transfer = nouveau_connector_aux_xfer;
>                 ret = drm_dp_aux_register(&nv_connector->aux);
>                 if (ret) {
> diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c
b/drivers/gpu/drm/nouveau/nouveau_drm.c
> index 2b2baf6e0e0d..4323e9e61c2e 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_drm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
> @@ -859,6 +859,7 @@ nouveau_pmops_runtime_suspend(struct device *dev)
>  {
>         struct pci_dev *pdev = to_pci_dev(dev);
>         struct drm_device *drm_dev = pci_get_drvdata(pdev);
> +       struct nouveau_drm *drm = nouveau_drm(drm_dev);
>         int ret;
>
>         if (!nouveau_pmops_runtime()) {
> @@ -866,6 +867,8 @@ nouveau_pmops_runtime_suspend(struct device *dev)
>                 return -EBUSY;
>         }
>
> +       drm->rpm_task = current;
> +
>         nouveau_switcheroo_optimus_dsm();
>         ret = nouveau_do_suspend(drm_dev, true);
>         pci_save_state(pdev);
> @@ -873,6 +876,8 @@ nouveau_pmops_runtime_suspend(struct device *dev)
>         pci_ignore_hotplug(pdev);
>         pci_set_power_state(pdev, PCI_D3cold);
>         drm_dev->switch_power_state = DRM_SWITCH_POWER_DYNAMIC_OFF;
> +
> +       drm->rpm_task = NULL;
>         return ret;
>  }
>
> @@ -881,6 +886,7 @@ nouveau_pmops_runtime_resume(struct device *dev)
>  {
>         struct pci_dev *pdev = to_pci_dev(dev);
>         struct drm_device *drm_dev = pci_get_drvdata(pdev);
> +       struct nouveau_drm *drm = nouveau_drm(drm_dev);
>         struct nvif_device *device =
&nouveau_drm(drm_dev)->client.device;
>         int ret;
>
> @@ -889,11 +895,13 @@ nouveau_pmops_runtime_resume(struct device *dev)
>                 return -EBUSY;
>         }
>
> +       drm->rpm_task = current;
> +
>         pci_set_power_state(pdev, PCI_D0);
>         pci_restore_state(pdev);
>         ret = pci_enable_device(pdev);
>         if (ret)
> -               return ret;
> +               goto out;
>         pci_set_master(pdev);
>
>         ret = nouveau_do_resume(drm_dev, true);
> @@ -905,6 +913,8 @@ nouveau_pmops_runtime_resume(struct device *dev)
>         /* Monitors may have been connected / disconnected during suspend
*/
>         schedule_work(&nouveau_drm(drm_dev)->hpd_work);
>
> +out:
> +       drm->rpm_task = NULL;
>         return ret;
>  }
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h
b/drivers/gpu/drm/nouveau/nouveau_drv.h
> index 0b2191fa96f7..e8d4203ddfb4 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_drv.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
> @@ -212,6 +212,8 @@ struct nouveau_drm {
>         bool have_disp_power_ref;
>
>         struct dev_pm_domain vga_pm_domain;
> +
> +       struct task_struct *rpm_task;
>  };
>
>  static inline struct nouveau_drm *
> @@ -231,6 +233,12 @@ int nouveau_pmops_suspend(struct device *);
>  int nouveau_pmops_resume(struct device *);
>  bool nouveau_pmops_runtime(void);
>
> +static inline bool
> +nouveau_is_rpm_worker(struct nouveau_drm *drm)
> +{
> +       return drm->rpm_task == current;
> +}
> +
>  #include <nvkm/core/tegra.h>
>
>  struct drm_device *
> --
> 2.19.1
>
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> Nouveau at lists.freedesktop.org
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