Re: [PATCH v2] vsp1: fix video output on R8A77970

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sergei,

On Monday, 15 January 2018 18:06:48 EET Sergei Shtylyov wrote:
> On 01/15/2018 03:51 PM, Laurent Pinchart wrote:
> > On Tuesday, 26 December 2017 23:14:12 EET Sergei Shtylyov wrote:
> >> Laurent has added support for the VSP2-D found on R-Car V3M (R8A77970)
> >> but
> > 
> > I'm not sure there's a need to state my name in the commit message.
> 
> You were the author of the patch this one has in the Fixes: tag, so I
> thought that was appropriate. I can remove that if you don't want you name
> mentioned...

It's just that I thought it was more important to refer to the patch than to 
my name, developers reading the log will be more interested in the technical 
details than in my person :-)

> >> the video  output that VSP2-D sends to DU has a greenish garbage-like
> >> line
> > 
> > Why does the text in your patches (commit message, comments, ...) sometime
> > have double spaces between words ?
> 
> The text looks more pleasant (at least to me). Can remove them if you
> want...

I don't think we try to do typesetting in kernel code or commit messages, so 
I'd stick to single spaces if you don't mind.

> >> repeated every 8 or so screen rows.
> > 
> > Is it every "8 or so" rows, or exactly every 8 rows ?
> 
> You really want me to count the pixels?

I'd like to know a bit more about the systems, whether the green lines appear 
at the exact same interval, whether they bounce up and down or are always at 
the same place, ...

> >> It turns out that V3M has a teeny LIF register (at least it's
> >> documented!) that you need to set to some kind of a  magic value for the
> >> LIF to work correctly...
> >> 
> >> Based on the original (and large) patch by Daisuke Matsushita
> >> <daisuke.matsushita.ns@hitachi.com>.
> > 
> > What else is in the big patch ? Is it available somewhere ?
> 
> Assorted changes gathered together only because they all bring the
> support for R8A77970. If you're really curious, here you are:
> 
> https://github.com/CogentEmbedded/meta-rcar/blob/v2.12.0/meta-rcar-gen3/reci
> pes-kernel/linux/linux-renesas/0030-arm64-renesas-r8a7797-Add-Renesas-R8A779
> 7-SoC-suppor.patch

Thank you.

> >> Fixes: d455b45f8393 ("v4l: vsp1: Add support for new VSP2-BS, VSP2-DL and
> >> VSP2-D instances")
> >> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
> >> 
> >> ---
> >> This patch is against the 'media_tree.git' repo's 'master' branch.
> >> 
> >> Changes in version 2:
> >> - added a  comment before the V3M SoC check;
> >> - fixed indetation in that check;
> >> - reformatted  the patch description.
> >> 
> >>   drivers/media/platform/vsp1/vsp1_lif.c  |   12 ++++++++++++
> >>   drivers/media/platform/vsp1/vsp1_regs.h |    5 +++++
> >>   2 files changed, 17 insertions(+)
> >> 
> >> Index: media_tree/drivers/media/platform/vsp1/vsp1_lif.c
> >> ===================================================================
> >> --- media_tree.orig/drivers/media/platform/vsp1/vsp1_lif.c
> >> +++ media_tree/drivers/media/platform/vsp1/vsp1_lif.c
> >> @@ -155,6 +155,18 @@ static void lif_configure(struct vsp1_en
> >>   			(obth << VI6_LIF_CTRL_OBTH_SHIFT) |
> >>   			(format->code == 0 ? VI6_LIF_CTRL_CFMT : 0) |
> >>   			VI6_LIF_CTRL_REQSEL | VI6_LIF_CTRL_LIF_EN);
> >> +
> >> +	/*
> >> +	 * R-Car V3M has the buffer attribute register you absolutely need
> >> +	 * to write kinda magic value to  for the LIF to work correctly...
> >> +	 */
> > 
> > I'm not sure about the "kinda" magic value. 1536 is very likely a buffer
> > size.
> 
> Well, that's only guessing. The manual doesn't say anything about what the
> number is.

Yes it's just an educated guess.

> > How about the following text ?
> > 
> > 	/*
> > 	
> > 	 * On V3M the LBA register has to be set to a non-default value to
> 
>     I'd then spell its full name, LIF0 Buffer Attribute register.

Sounds good to me.

> > 	 * guarantee proper operation (otherwise artifacts may appear on the
> > 	 * output). The value required by the datasheet is not documented but
> > 	 * is likely a buffer size or threshold.
> > 	 */
> 
> OK,  can change that (modulo the name).
> 
> > The commit message should also be updated to feel a bit less magic.
> 
> I'll see about it.
> 
> >> +	if ((entity->vsp1->version &
> >> +	     (VI6_IP_VERSION_MODEL_MASK | VI6_IP_VERSION_SOC_MASK)) ==
> >> +	    (VI6_IP_VERSION_MODEL_VSPD_V3 | VI6_IP_VERSION_SOC_V3M)) {
> >> +		vsp1_lif_write(lif, dl, VI6_LIF_LBA,
> >> +			       VI6_LIF_LBA_LBA0 |
> >> +			       (1536 << VI6_LIF_LBA_LBA1_SHIFT));
> >> +	}
> >> 
> >>   }
> > 
> > The datasheet documents the register as being present on both V3M and M3-W
> > (and the test I've just run on H3 shows that the register is present there
> > as well). Should we program it on M3-W or leave it to the default value
> > that should be what is recommended by the datasheet for that SoC ?
> 
> If the default value matches what's recommended by the manual, then I'd
> leave the register alone.

OK, I agree.

> But my task was R8A77970 support only anyway...

Sure, and my task is to push you to do more when it makes sense ;-)

-- 
Regards,

Laurent Pinchart