Document that DRM_MODE_PROP_IMMUTABLE must be set for the properties
that are immutable by definition - e.g. ranges with min == max or enums
with a single value. This matches the behaviour of the IGT tests, see
kms_properties.c / validate_range_prop(), validate_enum_prop(),
validate_bitmask_prop().

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---
 include/drm/drm_property.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/drm/drm_property.h b/include/drm/drm_property.h
index 082f29156b3e..d78ec42de42f 100644
--- a/include/drm/drm_property.h
+++ b/include/drm/drm_property.h
@@ -162,6 +162,9 @@ struct drm_property {
 	 *     userspace, e.g. the EDID, or the connector path property on DP
 	 *     MST sinks. Kernel can update the value of an immutable property
 	 *     by calling drm_object_property_set_value().
+	 *     This flag MUST be set for all properties that have only a
+	 *     single value (e.g. min == max or if enum has only a single
+	 *     value).
 	 */
 	uint32_t flags;
 

-- 
2.39.2

Hi,

On Mon, Jul 15, 2024 at 09:33:02AM GMT, Dmitry Baryshkov wrote:
> Document that DRM_MODE_PROP_IMMUTABLE must be set for the properties
> that are immutable by definition - e.g. ranges with min == max or enums
> with a single value. This matches the behaviour of the IGT tests, see
> kms_properties.c / validate_range_prop(), validate_enum_prop(),
> validate_bitmask_prop().
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

We had a discussion yesterday about it on IRC with Sima, Simon and
Xaver.

https://oftc.irclog.whitequark.org/dri-devel/2024-07-16#33374622;

The conclusion was that it would create an inconsistency between drivers
on whether a given property is immutable or not, which will lead to more
troubles for userspace.

It's not clear why Ville added that check in the first place, so the
best course of action is to remove the IGT test and get the discussion
started there.

Maxime

On Wed, Jul 17, 2024 at 03:42:46PM GMT, Maxime Ripard wrote:
> Hi,
> 
> On Mon, Jul 15, 2024 at 09:33:02AM GMT, Dmitry Baryshkov wrote:
> > Document that DRM_MODE_PROP_IMMUTABLE must be set for the properties
> > that are immutable by definition - e.g. ranges with min == max or enums
> > with a single value. This matches the behaviour of the IGT tests, see
> > kms_properties.c / validate_range_prop(), validate_enum_prop(),
> > validate_bitmask_prop().
> > 
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> 
> We had a discussion yesterday about it on IRC with Sima, Simon and
> Xaver.
> 
> https://oftc.irclog.whitequark.org/dri-devel/2024-07-16#33374622;
> 
> The conclusion was that it would create an inconsistency between drivers
> on whether a given property is immutable or not, which will lead to more
> troubles for userspace.
> 
> It's not clear why Ville added that check in the first place, so the
> best course of action is to remove the IGT test and get the discussion
> started there.

Ack, I'll work on removing those tests later today.

-- 
With best wishes
Dmitry