Re: [PATCH v2 4/4] media: aspeed: Fix timing polarity incorrect

[Jammy Huang]

On 2022/1/21 下午 03:30, Hans Verkuil wrote:
> On 12/22/21 09:21, Jammy Huang wrote:
> > This is a workaround for sync polarity unstable.
> > Sync value get by VR09C counts from sync's rising edge, which means
> > sync's polarity is negative if sync value is bigger than total/2.
> Do you have an example of such a format, or is this mostly theoretical?
>
> Either provide the example or make a note that it is theoretical.

OK, I will update an example in next patch. Let me explain first.

This is a must-be result. Please refer to the graph below as I sent in 
3/4 of this
series. For negative sync, sync width equals to back porch + data enable 
+ front porch.
Thus, sync would be bigger than 90% of total in most cases.

                  +-------------------+
                  |    v i d e o      |
      +--+  +-----+                   +-----+  +---+
         |  |                               |  |
         +--+                               +--+
       vsync+-------------------------------+
   frame_top+-----+
frame_bottom+-------------------------+


Following registers are what I got for 1920x1200@60.

1e700090: 07ee206f 04c9001a c4d3efff 04cc001f

1e7000a0: 0000081f 00000000 00000000 00000000

vertical total = 0x4D3 (VR098[27:16]) = 1235
vertical sync = 0x4CC (VR09C[27:16]) = 1228

> Regards,
>
> 	Hans
>
> > Signed-off-by: Jammy Huang <jammy_huang@xxxxxxxxxxxxxx>
> > ---
> >   v2:
> >    - Use 'total/2' rather than 'total<<1'
> >    - Update comment
> > ---
> >   drivers/media/platform/aspeed-video.c | 20 ++++++++++++++++++++
> >   1 file changed, 20 insertions(+)
> >
> > diff --git a/drivers/media/platform/aspeed-video.c b/drivers/media/platform/aspeed-video.c
> > index 7c50567f5ab0..c3e3343d91e1 100644
> > --- a/drivers/media/platform/aspeed-video.c
> > +++ b/drivers/media/platform/aspeed-video.c
> > @@ -989,6 +989,16 @@ static void aspeed_video_get_resolution(struct aspeed_video *video)
> >   
> >   		video->frame_bottom = FIELD_GET(VE_SRC_TB_EDGE_DET_BOT, src_tb_edge);
> >   		video->frame_top = FIELD_GET(VE_SRC_TB_EDGE_DET_TOP, src_tb_edge);
> > +
> > +		/*
> > +		 * This is a workaround for polarity detection when the sync
> > +		 * value is larger than half.
> > +		 */
> > +		if (vsync > (vtotal / 2))
> > +			det->polarities &= ~V4L2_DV_VSYNC_POS_POL;
> > +		else
> > +			det->polarities |= V4L2_DV_VSYNC_POS_POL;
> > +
> >   		if (det->polarities & V4L2_DV_VSYNC_POS_POL) {
> >   			det->vbackporch = video->frame_top - vsync;
> >   			det->vfrontporch = vtotal - video->frame_bottom;
> > @@ -1003,6 +1013,16 @@ static void aspeed_video_get_resolution(struct aspeed_video *video)
> >   
> >   		video->frame_right = FIELD_GET(VE_SRC_LR_EDGE_DET_RT, src_lr_edge);
> >   		video->frame_left = FIELD_GET(VE_SRC_LR_EDGE_DET_LEFT, src_lr_edge);
> > +
> > +		/*
> > +		 * This is a workaround for polarity detection when the sync
> > +		 * value is larger than half.
> > +		 */
> > +		if (hsync > (htotal / 2))
> > +			det->polarities &= ~V4L2_DV_HSYNC_POS_POL;
> > +		else
> > +			det->polarities |= V4L2_DV_HSYNC_POS_POL;
> > +
> >   		if (det->polarities & V4L2_DV_HSYNC_POS_POL) {
> >   			det->hbackporch = video->frame_left - hsync;
> >   			det->hfrontporch = htotal - video->frame_right;

--
Best Regards
Jammy