[U-Boot] [PATCH v2 4/4] sunxi: video: Add H3/H5 TV out driver

[Maxime Ripard]

On Wed, May 24, 2017 at 05:34:52PM +0200, Jernej Škrabec wrote:
> Hi,
> 
> Dne torek, 23. maj 2017 ob 22:22:14 CEST je Maxime Ripard napisal(a):
> > Hi Jernej,
> > 
> > On Mon, May 22, 2017 at 08:49:57PM +0200, Jernej Škrabec wrote:
> > > Dne ponedeljek, 22. maj 2017 ob 09:35:56 CEST je Maxime Ripard napisal(a):
> > > > On Fri, May 19, 2017 at 05:41:17PM +0200, Jernej Skrabec wrote:
> > > > > This commit adds support for TV (composite) output.
> > > > > 
> > > > > Because there is no mechanism to select TV standard, PAL is
> > > > > hardcoded.
> > > > 
> > > > I'd rather use a consistent mechanism with the old driver (even if we
> > > > only support PAL right now and reject any other option), and using
> > > > composite-pal as monitor.
> > > 
> > > I have few arguments against that:
> > > 
> > > 1. Code for parsing that env variable is in videomodes.[c|h], which is
> > > clearly a part of an older video framework (ctfb). I didn't want to
> > > include any legacy code.
> > > 
> > > 2. Even if this code is used for parsing, it would bring a lot of
> > > confusion. For now, we can say that docs/README.video does not apply to
> > > H3 and newer SoCs. If we implement this only partially, we would need to
> > > describe in details which of each setting is honored with the new driver
> > > and which not. Even then, a lot of users would skip that description and
> > > complain anyway.
> > The issue with this, and we've been bitten very hard on this one with
> > the CHIP, is that you don't really have a clear majority on that
> > one. If you support only PAL, half the world will be left out, and
> > same thing with NTSC (for some reason, we never needed to support the
> > less common ones like PAL-M or NTSC-J, but that just might be because
> > it never really sold that well in those countries, I don't have any
> > numbers on that).
> > 
> > The point is, if you just hardcode PAL for now, you will have half
> > your users complain, and then, when we will introduce NTSC support
> > eventually, we'll have to introduce some mechanism to switch between
> > the two, then we'll probably break the behaviour our users relied on
> > before, making the other half of our users pissed.
> > 
> > I'm not sure this is something we should just discard, or at least the
> > second part. Having the selection mechanism in place, even if we don't
> > support all the settings and just report an error in the logs in such
> > a case address the latter issue.
> > 
> > You'll also need to address how to setup the overscan, since this is
> > really something you want to have very quick.
> 
> Ok, I'm prepared to tackle this. Do you think it is worth to delay driver 
> merge?

Not per se, but that should definitely be part of the same release, so
if you can make it by then, then we can merge that right now, and
merge the rest later. If you can't, then we'll have to postpone it a
bit.

> > > 3. If anything is done in this direction, I think that it is better
> > > to extend DM video framework so other drivers would benefit from
> > > that work too.
> > 
> > That makes sense, but again, this is a pre-requisite for me. And it's
> > not that hard to support the video modelines with a device model
> > driver, Linux does it, and you have a string identifier at the
> > beginning of it. It just has to be deterministic, but I don't think
> > this is an issue with U-Boot's DM.
> 
> Ok, so how do you think we should implement this? If only composite
> modes are supported in the string, someone might try to set hdmi
> monitor. Should we just ignore such settings and maybe print a
> warning?

I'm not sure it was your question, but I would just reject any
improper configuration, and not display anything in such a case.

> Also the question for Simon, how should I merge code for parsing
> video string from drivers/video/videomodes.c to DM video in a way to
> be useful to most drivers?
> 
> I guess this is the first time to support analog video output in DM
> video driver and there are some things missing such as a way to
> select TV standard and define overscan.

I think it can be done in the same way linux does it here:
http://elixir.free-electrons.com/linux/latest/source/drivers/video/fbdev/core/fb_cmdline.c#L35

You basically check first that there is a string matching what your
driver expects, and then get the options.

We could imagine having some extra function to parse that string and
give back a structure filled with whatever was set in that command
line. We could imagine having the common custom properties to be
parsed at that same time.

> Or alternatively, I could make just quick edit to sunxi_tve.c driver
> and directly use old functions as they are. That way we could get
> something working very quickly, but I don't like much such approach.

That's another approach, I'm fine with it as a temporary measure, but
I'm not sure how Simon feels about it.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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