Re: [PATCH 3/3] rcar-vin: Add support for RGB formats with alpha component

["Niklas Söderlund" <niklas.soderlund@ragnatech.se>]

Hi Laurent,

Thanks for your feedback.

On 2019-05-16 13:08:22 +0300, Laurent Pinchart wrote:
> Hi Niklas,
> 
> Thank you for the patch.
> 
> On Thu, May 16, 2019 at 02:47:46AM +0200, Niklas Söderlund wrote:
> > The R-Car VIN module supports V4L2_PIX_FMT_ARGB555 and
> > V4L2_PIX_FMT_ABGR32 pixel formats. Add the hardware register setup and
> > allow the alpha component to be changed while streaming using the
> > V4L2_CID_ALPHA_COMPONENT control.
> > 
> > Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> > ---
> >  drivers/media/platform/rcar-vin/rcar-dma.c  | 30 +++++++++++++++++++++
> >  drivers/media/platform/rcar-vin/rcar-v4l2.c |  8 ++++++
> >  2 files changed, 38 insertions(+)
> > 
> > diff --git a/drivers/media/platform/rcar-vin/rcar-dma.c b/drivers/media/platform/rcar-vin/rcar-dma.c
> > index 4e991cce5fb56a90..5c0ed27c5d05dd45 100644
> > --- a/drivers/media/platform/rcar-vin/rcar-dma.c
> > +++ b/drivers/media/platform/rcar-vin/rcar-dma.c
> > @@ -111,8 +111,11 @@
> >  #define VNIE_EFE		(1 << 1)
> >  
> >  /* Video n Data Mode Register bits */
> > +#define VNDMR_A8BIT(n)		((n & 0xff) << 24)
> > +#define VNDMR_A8BIT_MASK	(0xff << 24)
> >  #define VNDMR_EXRGB		(1 << 8)
> >  #define VNDMR_BPSM		(1 << 4)
> > +#define VNDMR_ABIT		(1 << 2)
> >  #define VNDMR_DTMD_YCSEP	(1 << 1)
> >  #define VNDMR_DTMD_ARGB		(1 << 0)
> >  
> > @@ -730,6 +733,12 @@ static int rvin_setup(struct rvin_dev *vin)
> >  		/* Note: not supported on M1 */
> >  		dmr = VNDMR_EXRGB;
> >  		break;
> > +	case V4L2_PIX_FMT_ARGB555:
> > +		dmr = (vin->alpha ? VNDMR_ABIT : 0) | VNDMR_DTMD_ARGB;
> > +		break;
> > +	case V4L2_PIX_FMT_ABGR32:
> > +		dmr = VNDMR_A8BIT(vin->alpha) | VNDMR_EXRGB | VNDMR_DTMD_ARGB;
> > +		break;
> >  	default:
> >  		vin_err(vin, "Invalid pixelformat (0x%x)\n",
> >  			vin->format.pixelformat);
> > @@ -1346,5 +1355,26 @@ int rvin_set_channel_routing(struct rvin_dev *vin, u8 chsel)
> >  
> >  void rvin_set_alpha(struct rvin_dev *vin, unsigned int alpha)
> 
> OK, I now see why you added a rvin_set_alpha() function. It makes sense,
> but I think you need to protect this with a lock to avoid races between
> stream start and control set. Or are we already protected by a lock the
> serialises all V4L2 ioctls for the VIN video node ?

Yes we are protected by the ioctls lock in __video_do_ioctl(), at least 
that is my interpretation of the code I have not tried to force a race.

> 
> >  {
> > +	u32 dmr;
> > +
> >  	vin->alpha = alpha;
> > +
> > +	if (vin->state == STOPPED)
> > +		return;
> > +
> > +	switch (vin->format.pixelformat) {
> > +	case V4L2_PIX_FMT_ARGB555:
> > +		dmr = rvin_read(vin, VNDMR_REG) & ~VNDMR_ABIT;
> > +		if (vin->alpha)
> > +			dmr |= VNDMR_ABIT;
> > +		break;
> 
> Should you cache the DNDMR valid to avoid a hardware read ?

It is one possibility, as VNDMR is written to at other locations I would 
feel better to to this at a later point in time.

I'm currently trying to clean up the rcar-vin driver with regard to how 
it handles formats a bit different in the devnode and media centric code 
paths. Once that work is complete a generic way to cache register values 
could be added on top. I suspect there are other registers then VNDMR 
which could benefit from such a solution.

> 
> > +	case V4L2_PIX_FMT_ABGR32:
> > +		dmr = rvin_read(vin, VNDMR_REG) & ~VNDMR_A8BIT_MASK;
> > +		dmr |= VNDMR_A8BIT(vin->alpha);
> > +		break;
> > +	default:
> > +		return;
> > +	}
> > +
> > +	rvin_write(vin, dmr,  VNDMR_REG);
> >  }
> > diff --git a/drivers/media/platform/rcar-vin/rcar-v4l2.c b/drivers/media/platform/rcar-vin/rcar-v4l2.c
> > index 7cbdcbf9b090c638..bb2900f5d000f9a6 100644
> > --- a/drivers/media/platform/rcar-vin/rcar-v4l2.c
> > +++ b/drivers/media/platform/rcar-vin/rcar-v4l2.c
> > @@ -54,6 +54,14 @@ static const struct rvin_video_format rvin_formats[] = {
> >  		.fourcc			= V4L2_PIX_FMT_XBGR32,
> >  		.bpp			= 4,
> >  	},
> > +	{
> > +		.fourcc			= V4L2_PIX_FMT_ARGB555,
> > +		.bpp			= 2,
> > +	},
> > +	{
> > +		.fourcc			= V4L2_PIX_FMT_ABGR32,
> > +		.bpp			= 4,
> > +	},
> >  };
> >  
> >  const struct rvin_video_format *rvin_format_from_pixel(u32 pixelformat)
> 
> -- 
> Regards,
> 
> Laurent Pinchart

-- 
Regards,
Niklas Söderlund