[U-Boot] [RFC PATCH 2/3] sunxi: video: Add video driver for H3 SoC

[Maxime Ripard]

Hi,

On Tue, Dec 13, 2016 at 09:13:11PM +0100, Jernej Škrabec wrote:
> Hi,
> 
> On Tue, Dec 13, 2016 at 16:40:55 CET, Maxime Ripard wrote:
> > Hi,
> > 
> > On Tue, Dec 13, 2016 at 01:36:29AM +0100, Jernej Skrabec wrote:
> > > This patch adds support for hdmi output. It is designed in the same
> > > way as video driver for older Allwinner SoCs.
> > > 
> > > First it checks if monitor is attached. If it is, recommended
> > > timings are read from EDID. After that, DE2, TCON and HDMI are
> > > configured according to this timings.
> > > 
> > > 32MB of RAM is used for framebuffer. This is just enough to support
> > > 4K resolution.
> > > 
> > > SimpleFB is also supported by this driver.
> > > 
> > > Signed-off-by: Jernej Skrabec <jernej.skrabec at siol.net>
> > 
> > From the linux discussion, I recall that you said that the TCON was
> > still the same, and the HDMI was something that could be shared with
> > the Rockchip implementation. Did you look into sharing the TCON code
> > (for example using a small "library" to share the functions) and to
> > reuse Rockchip's HDMI code?
> 
> For now, I only reused one TCON function and some defines. I tought that split 
> would be better done a bit later, when the driver will get support for LCD 
> screens (A64, for example). At that time TCON code would also be refactored to 
> be more generic and properly tested that it can be used with both drivers. 
> Unfortunatelly, I don't have any board with older SoC for testing.

We can definitely do that. I think I have access to at least of board
of each generation, so I can totally test whatever you come up with on
those boards, and help you debugging whatever issue that might show up.

> While I took Rockchip HDMI code for reference, it can't be easily reused. 
> First of, it uses DT nodes. I guess I could write DT binding or modify 
> existing driver to work without it.

Like we discussed in the other part of the thread, I think the latter
would be easier to deal with.

> Second issue here is same as in Linux, PHY code is tightly coupled
> with controller code, so it needs to be decoupled first.

But it would be easier to deal with than Linux I guess. Can't you just
create a new weak function to initialise the phy? And then, every
platform can just overwrite it.

> Thirdly, and in my opinion most annoying, Rockchip driver uses 32
> bit aligned registers, but H3 does not. This also means a lot of
> work to make it more generic.

How does Linux deal with that? Would just using some kind of accessors
that would abstract that away from the driver help, or is it more
complicated?

> Actually, H3 is more similar to i.MX6 HDMI in this regard, but
> driver's code is scattered throughout multiple files (search for
> mxc_hdmi.h inclusion). It is certainly doable, but it will take much
> more time.  Basically, U-Boot already has two drivers for DWC HDMI
> and with this patch it will get third. Merging all three
> implementations into one would be very tedious, but very desirable
> goal. I must state that I didn't really try to understand i.MX6 HDMI
> code at all, so I don't now how hard it would be to pull it out.

I'm not sure that merging a third and saying that it would be up to
the fourth to do the work is reasonable. It's just hiding an issue
under the carpet, but I don't see how it will be easier for the next
person to work on that. Quite the opposite actually.

Maxime

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