Re: [PATCH 1/2] drm: Add DRM_MODE_FB_BFF flag definition

[Vincent ABRIOU <vincent.abriou@st.com>]

On 02/29/2016 04:32 PM, Daniel Vetter wrote:
> On Fri, Feb 26, 2016 at 11:33:08AM +0100, Vincent ABRIOU wrote:
>> Hi,
>>
>> Have you any comment for this proposal?
>
> I guess since we don't really have userspace that uses interlaced modes,
> much less actually bothers to get the fields correct I think just have
> some (open-source) userspace somewhere (does gstreamer care enough about
> this?) which needs this and it's good.
>

Hi Daniel,

At Gstreamer side, an interlaced GstBuffer could be tagged with flags:
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-base-libs/html/gst-plugins-base-libs-gstvideo.html#GstVideoFrameFlags

GST_VIDEO_FRAME_FLAG_TFF is one of them and it is used to warn that the 
buffer is interlaced with Top Field First (TFF).

At kernel side, we preferred to tag the interlaced buffer with Bottom 
Field First (BFF) because most of the interlaced buffer are TFF and that 
BFF are the exception.

Further, we made tests with weston to validate the full path and it is 
working fine.

BR
Vincent

> Without userspace this is a hard sell.
>
> Thanks, Daniel
>
>>
>> BR
>> Vincent
>>
>> On 02/12/2016 10:26 AM, Vincent Abriou wrote:
>>> From: Fabien Dessenne <fabien.dessenne@st.com>
>>>
>>> If a buffer is interlaced, this "Bottom Field First" flag specifies
>>> which of the top or the bottom field shall be displayed first.
>>> When set, the bottom field shall be displayed first.
>>> When unset the top field shall be displayed first.
>>>
>>> Signed-off-by: Fabien Dessenne <fabien.dessenne@st.com>
>>> ---
>>>    drivers/gpu/drm/drm_crtc.c  | 3 ++-
>>>    include/uapi/drm/drm_mode.h | 1 +
>>>    2 files changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
>>> index d40bab2..64b4fdac 100644
>>> --- a/drivers/gpu/drm/drm_crtc.c
>>> +++ b/drivers/gpu/drm/drm_crtc.c
>>> @@ -3315,7 +3315,8 @@ internal_framebuffer_create(struct drm_device *dev,
>>>    	struct drm_framebuffer *fb;
>>>    	int ret;
>>>
>>> -	if (r->flags & ~(DRM_MODE_FB_INTERLACED | DRM_MODE_FB_MODIFIERS)) {
>>> +	if (r->flags & ~(DRM_MODE_FB_INTERLACED | DRM_MODE_FB_MODIFIERS
>>> +			| DRM_MODE_FB_BFF)) {
>>>    		DRM_DEBUG_KMS("bad framebuffer flags 0x%08x\n", r->flags);
>>>    		return ERR_PTR(-EINVAL);
>>>    	}
>>> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>>> index 50adb46..f7c9111 100644
>>> --- a/include/uapi/drm/drm_mode.h
>>> +++ b/include/uapi/drm/drm_mode.h
>>> @@ -354,6 +354,7 @@ struct drm_mode_fb_cmd {
>>>
>>>    #define DRM_MODE_FB_INTERLACED	(1<<0) /* for interlaced framebuffers */
>>>    #define DRM_MODE_FB_MODIFIERS	(1<<1) /* enables ->modifer[] */
>>> +#define DRM_MODE_FB_BFF		(1<<2) /* if interlaced, bottom field first */
>>>
>>>    struct drm_mode_fb_cmd2 {
>>>    	__u32 fb_id;
>>>
>
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