[PATCH] drm/connector: demote connector force-probes for non-master clients

[PATCH] drm/connector: demote connector force-probes for non-master clients

[Simon Ser]

Force-probing a connector can be slow and cause flickering. As this
affects the global KMS state, let's make it so only the DRM master
can force-probe a connector.

Non-master DRM clients won't be able to force-probe a connector
anymore. Instead, KMS will perform a regular read-only connector
query.

Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
---
 drivers/gpu/drm/drm_connector.c | 11 ++++++++---
 include/uapi/drm/drm_mode.h     |  7 ++++---
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 7631f76e7f34..2f70a52a892b 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -20,6 +20,7 @@
  * OF THIS SOFTWARE.
  */
 
+#include <drm/drm_auth.h>
 #include <drm/drm_connector.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_encoder.h>
@@ -2374,9 +2375,13 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
 
 	mutex_lock(&dev->mode_config.mutex);
 	if (out_resp->count_modes == 0) {
-		connector->funcs->fill_modes(connector,
-					     dev->mode_config.max_width,
-					     dev->mode_config.max_height);
+		if (drm_is_current_master(file_priv))
+			connector->funcs->fill_modes(connector,
+						     dev->mode_config.max_width,
+						     dev->mode_config.max_height);
+		else
+			drm_dbg_kms(dev, "User-space requested a forced probe on [CONNECTOR:%d:%s] but is not the DRM master, demoting to read-only probe",
+				    connector->base.id, connector->name);
 	}
 
 	out_resp->mm_width = connector->display_info.width_mm;
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index a5e76aa06ad5..3efa2e38d89b 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -413,9 +413,10 @@ enum drm_mode_subconnector {
  *
  * **Force-probing a connector**
  *
- * If the @count_modes field is set to zero, the kernel will perform a forced
- * probe on the connector to refresh the connector status, modes and EDID.
- * A forced-probe can be slow, might cause flickering and the ioctl will block.
+ * If the @count_modes field is set to zero and the DRM client is the DRM
+ * master, the kernel will perform a forced probe on the connector to refresh
+ * the connector status, modes and EDID. A forced-probe can be slow, might
+ * cause flickering and the ioctl will block.
  *
  * User-space needs to force-probe connectors to ensure their metadata is
  * up-to-date at startup and after receiving a hot-plug event. User-space
-- 
2.31.1

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Re: [PATCH] drm/connector: demote connector force-probes for non-master clients

[Pekka Paalanen]

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On Fri,  2 Apr 2021 13:22:12 +0200
Simon Ser <contact@emersion.fr> wrote:

> Force-probing a connector can be slow and cause flickering. As this
> affects the global KMS state, let's make it so only the DRM master
> can force-probe a connector.
> 
> Non-master DRM clients won't be able to force-probe a connector
> anymore. Instead, KMS will perform a regular read-only connector
> query.
> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: Pekka Paalanen <ppaalanen@gmail.com>

Hi,

seems like a good idea to me.
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>

Btw. can force-probe be triggered via sysfs as well and does it require
root privs?


Thanks,
pq


> ---
>  drivers/gpu/drm/drm_connector.c | 11 ++++++++---
>  include/uapi/drm/drm_mode.h     |  7 ++++---
>  2 files changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 7631f76e7f34..2f70a52a892b 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -20,6 +20,7 @@
>   * OF THIS SOFTWARE.
>   */
>  
> +#include <drm/drm_auth.h>
>  #include <drm/drm_connector.h>
>  #include <drm/drm_edid.h>
>  #include <drm/drm_encoder.h>
> @@ -2374,9 +2375,13 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
>  
>  	mutex_lock(&dev->mode_config.mutex);
>  	if (out_resp->count_modes == 0) {
> -		connector->funcs->fill_modes(connector,
> -					     dev->mode_config.max_width,
> -					     dev->mode_config.max_height);
> +		if (drm_is_current_master(file_priv))
> +			connector->funcs->fill_modes(connector,
> +						     dev->mode_config.max_width,
> +						     dev->mode_config.max_height);
> +		else
> +			drm_dbg_kms(dev, "User-space requested a forced probe on [CONNECTOR:%d:%s] but is not the DRM master, demoting to read-only probe",
> +				    connector->base.id, connector->name);
>  	}
>  
>  	out_resp->mm_width = connector->display_info.width_mm;
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index a5e76aa06ad5..3efa2e38d89b 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -413,9 +413,10 @@ enum drm_mode_subconnector {
>   *
>   * **Force-probing a connector**
>   *
> - * If the @count_modes field is set to zero, the kernel will perform a forced
> - * probe on the connector to refresh the connector status, modes and EDID.
> - * A forced-probe can be slow, might cause flickering and the ioctl will block.
> + * If the @count_modes field is set to zero and the DRM client is the DRM
> + * master, the kernel will perform a forced probe on the connector to refresh
> + * the connector status, modes and EDID. A forced-probe can be slow, might
> + * cause flickering and the ioctl will block.
>   *
>   * User-space needs to force-probe connectors to ensure their metadata is
>   * up-to-date at startup and after receiving a hot-plug event. User-space


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Re: [PATCH] drm/connector: demote connector force-probes for non-master clients

[Simon Ser]

On Wednesday, April 7th, 2021 at 9:02 AM, Pekka Paalanen <ppaalanen@gmail.com> wrote:

> Btw. can force-probe be triggered via sysfs as well and does it require
> root privs?

sysfs can force-probe like so:

    echo detect | sudo tee /sys/class/drm/card0-DP-1/status

But this requires root, yes.
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Re: [PATCH] drm/connector: demote connector force-probes for non-master clients

[Pekka Paalanen]

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On Wed, 07 Apr 2021 07:16:30 +0000
Simon Ser <contact@emersion.fr> wrote:

> On Wednesday, April 7th, 2021 at 9:02 AM, Pekka Paalanen <ppaalanen@gmail.com> wrote:
> 
> > Btw. can force-probe be triggered via sysfs as well and does it require
> > root privs?  
> 
> sysfs can force-probe like so:
> 
>     echo detect | sudo tee /sys/class/drm/card0-DP-1/status
> 
> But this requires root, yes.

Ah, all good then.


Thanks,
pq

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Re: [PATCH] drm/connector: demote connector force-probes for non-master clients

[Simon Ser]

Ping Daniel Vetter
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Re: [PATCH] drm/connector: demote connector force-probes for non-master clients

[Daniel Vetter]

On Fri, Apr 02, 2021 at 01:22:12PM +0200, Simon Ser wrote:
> Force-probing a connector can be slow and cause flickering. As this
> affects the global KMS state, let's make it so only the DRM master
> can force-probe a connector.
> 
> Non-master DRM clients won't be able to force-probe a connector
> anymore. Instead, KMS will perform a regular read-only connector
> query.
> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: Pekka Paalanen <ppaalanen@gmail.com>
> ---
>  drivers/gpu/drm/drm_connector.c | 11 ++++++++---
>  include/uapi/drm/drm_mode.h     |  7 ++++---
>  2 files changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 7631f76e7f34..2f70a52a892b 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -20,6 +20,7 @@
>   * OF THIS SOFTWARE.
>   */
>  
> +#include <drm/drm_auth.h>
>  #include <drm/drm_connector.h>
>  #include <drm/drm_edid.h>
>  #include <drm/drm_encoder.h>
> @@ -2374,9 +2375,13 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
>  
>  	mutex_lock(&dev->mode_config.mutex);
>  	if (out_resp->count_modes == 0) {
> -		connector->funcs->fill_modes(connector,
> -					     dev->mode_config.max_width,
> -					     dev->mode_config.max_height);
> +		if (drm_is_current_master(file_priv))
> +			connector->funcs->fill_modes(connector,
> +						     dev->mode_config.max_width,
> +						     dev->mode_config.max_height);
> +		else
> +			drm_dbg_kms(dev, "User-space requested a forced probe on [CONNECTOR:%d:%s] but is not the DRM master, demoting to read-only probe",
> +				    connector->base.id, connector->name);
>  	}
>  
>  	out_resp->mm_width = connector->display_info.width_mm;
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index a5e76aa06ad5..3efa2e38d89b 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -413,9 +413,10 @@ enum drm_mode_subconnector {
>   *
>   * **Force-probing a connector**
>   *
> - * If the @count_modes field is set to zero, the kernel will perform a forced
> - * probe on the connector to refresh the connector status, modes and EDID.
> - * A forced-probe can be slow, might cause flickering and the ioctl will block.
> + * If the @count_modes field is set to zero and the DRM client is the DRM

*current* DRM master

The drm master/client relationship survives a DROPMASTER ioctl, but also
it's only really relevant for the old authmagic dance. But just to be
consistent here.

> + * master, the kernel will perform a forced probe on the connector to refresh
> + * the connector status, modes and EDID. A forced-probe can be slow, might
> + * cause flickering and the ioctl will block.

Do we have an igt for this? Timing test should do the job I think,
assuming we have at least one output which requires an edid read (so maybe
skip the test if a forced probe takes less than 10ms or so).

Patch lgtm, but igt would be really nice here.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

>   *
>   * User-space needs to force-probe connectors to ensure their metadata is
>   * up-to-date at startup and after receiving a hot-plug event. User-space
> -- 
> 2.31.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH] drm/connector: demote connector force-probes for non-master clients

[Simon Ser]

On Tuesday, April 20th, 2021 at 11:14 AM, Daniel Vetter <daniel@ffwll.ch> wrote:

> Do we have an igt for this? Timing test should do the job I think,
> assuming we have at least one output which requires an edid read (so maybe
> skip the test if a forced probe takes less than 10ms or so).

Err, an igt that only relies on timings? Sorry, but that sounds like a
recipe for flaky tests.

Ideally a chamelium test would allow to make sure all of this works as
expected. I don't really have this hw anymore though.
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