* [PATCH] drm: document drm_property_enum.value for bitfields
@ 2021-07-21 6:51 Simon Ser
2021-07-21 11:43 ` Daniel Vetter
0 siblings, 1 reply; 3+ messages in thread
From: Simon Ser @ 2021-07-21 6:51 UTC (permalink / raw)
To: dri-devel; +Cc: Daniel Vetter, Pekka Paalanen, Leandro Ribeiro
When a property has the type DRM_MODE_PROP_BITMASK, the value field
stores a bitshift, not a bitmask, which can be surprising.
Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Pekka Paalanen <pekka.paalanen@collabora.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Leandro Ribeiro <leandro.ribeiro@collabora.com>
---
include/drm/drm_property.h | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/include/drm/drm_property.h b/include/drm/drm_property.h
index bbf5c1fdd7b0..f3ea7f97f372 100644
--- a/include/drm/drm_property.h
+++ b/include/drm/drm_property.h
@@ -37,6 +37,11 @@
*
* For enumeration and bitmask properties this structure stores the symbolic
* decoding for each value. This is used for example for the rotation property.
+ *
+ * If the property has the type &DRM_MODE_PROP_BITMASK, @value stores a
+ * bitshift, not a bitmask. In other words, the enum entry is enabled if the
+ * bit number @value is set in the property's value. This enum entry has the
+ * bitmask ``1 << value``.
*/
struct drm_property_enum {
uint64_t value;
--
2.32.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] drm: document drm_property_enum.value for bitfields
2021-07-21 6:51 [PATCH] drm: document drm_property_enum.value for bitfields Simon Ser
@ 2021-07-21 11:43 ` Daniel Vetter
2021-07-22 7:34 ` Pekka Paalanen
0 siblings, 1 reply; 3+ messages in thread
From: Daniel Vetter @ 2021-07-21 11:43 UTC (permalink / raw)
To: Simon Ser; +Cc: Daniel Vetter, Pekka Paalanen, Leandro Ribeiro, dri-devel
On Wed, Jul 21, 2021 at 06:51:30AM +0000, Simon Ser wrote:
> When a property has the type DRM_MODE_PROP_BITMASK, the value field
> stores a bitshift, not a bitmask, which can be surprising.
>
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Cc: Pekka Paalanen <pekka.paalanen@collabora.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Leandro Ribeiro <leandro.ribeiro@collabora.com>
> ---
> include/drm/drm_property.h | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/include/drm/drm_property.h b/include/drm/drm_property.h
> index bbf5c1fdd7b0..f3ea7f97f372 100644
> --- a/include/drm/drm_property.h
> +++ b/include/drm/drm_property.h
> @@ -37,6 +37,11 @@
> *
> * For enumeration and bitmask properties this structure stores the symbolic
> * decoding for each value. This is used for example for the rotation property.
> + *
> + * If the property has the type &DRM_MODE_PROP_BITMASK, @value stores a
> + * bitshift, not a bitmask. In other words, the enum entry is enabled if the
> + * bit number @value is set in the property's value. This enum entry has the
> + * bitmask ``1 << value``.
Please move this into an inline comment to make it clear that this is
specifically about @value. With that:
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
I was also pondering whether we have a nice place to link to for
"property's value" but really they're just uint64_t all over the place,
and only stored in the drm_mode_object for non-atomic properties. So
wording sounds like the best option we have.
> */
> struct drm_property_enum {
> uint64_t value;
> --
> 2.32.0
>
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] drm: document drm_property_enum.value for bitfields
2021-07-21 11:43 ` Daniel Vetter
@ 2021-07-22 7:34 ` Pekka Paalanen
0 siblings, 0 replies; 3+ messages in thread
From: Pekka Paalanen @ 2021-07-22 7:34 UTC (permalink / raw)
To: Simon Ser; +Cc: Daniel Vetter, dri-devel, Leandro Ribeiro
[-- Attachment #1: Type: text/plain, Size: 1922 bytes --]
On Wed, 21 Jul 2021 13:43:05 +0200
Daniel Vetter <daniel@ffwll.ch> wrote:
> On Wed, Jul 21, 2021 at 06:51:30AM +0000, Simon Ser wrote:
> > When a property has the type DRM_MODE_PROP_BITMASK, the value field
> > stores a bitshift, not a bitmask, which can be surprising.
> >
> > Signed-off-by: Simon Ser <contact@emersion.fr>
> > Cc: Pekka Paalanen <pekka.paalanen@collabora.com>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Cc: Leandro Ribeiro <leandro.ribeiro@collabora.com>
> > ---
> > include/drm/drm_property.h | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/include/drm/drm_property.h b/include/drm/drm_property.h
> > index bbf5c1fdd7b0..f3ea7f97f372 100644
> > --- a/include/drm/drm_property.h
> > +++ b/include/drm/drm_property.h
> > @@ -37,6 +37,11 @@
> > *
> > * For enumeration and bitmask properties this structure stores the symbolic
> > * decoding for each value. This is used for example for the rotation property.
> > + *
> > + * If the property has the type &DRM_MODE_PROP_BITMASK, @value stores a
> > + * bitshift, not a bitmask. In other words, the enum entry is enabled if the
> > + * bit number @value is set in the property's value. This enum entry has the
> > + * bitmask ``1 << value``.
>
> Please move this into an inline comment to make it clear that this is
> specifically about @value. With that:
>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>
With that
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Thanks,
pq
> I was also pondering whether we have a nice place to link to for
> "property's value" but really they're just uint64_t all over the place,
> and only stored in the drm_mode_object for non-atomic properties. So
> wording sounds like the best option we have.
>
> > */
> > struct drm_property_enum {
> > uint64_t value;
> > --
> > 2.32.0
> >
> >
>
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2021-07-21 6:51 [PATCH] drm: document drm_property_enum.value for bitfields Simon Ser
2021-07-21 11:43 ` Daniel Vetter
2021-07-22 7:34 ` Pekka Paalanen
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