Re: [PATCHv2 23/27] OMAPDSS: connector-dvi: Add DT support

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On 2013-12-17 17:15, Laurent Pinchart wrote:

>>> Either the driver is too specific or the binding is too generic, but
>>> having such a generic name for an omap specific driver seems wrong. Same
>>> for panel-dpi, svideo-connector, composite-video-connector and
>>> hdmi-connector,
>>
>> Hmm. Good point. I was thinking that the driver is only used on OMAP, but of
>> course that's not true, the driver is there for all platforms if the kernel
>> just happens to be compiled with the driver.
>>
>> And it's not just about those drivers you mention. The same issue is there
>> for, say, "ti,tpd12s015". I have an omapdss specific driver for that, but if
>> some other platform uses the same chip, they'll have a driver for it also...
>>
>> Sigh. I wonder how this should be handled... The only solution that comes to
>> my mind is to have all the compatible strings as "ti,...". But that's not
>> correct, as they are not TI components, but some are generic ones and some
>> from another vendor.
>>
>> And even "ti,..." is not good, as there are other TI SoCs with other display
>> drivers. So I'd need to prepend the compatible strings with "omapdss,...",
>> making the hardware components driver specific.
>>
>> The long term plan is to make the drivers generic (or implement the same
>> driver for common display framework). But for now I need to have future
>> proof DT bindings with omapdss specific drivers...
> 
> I'll refrain from mentioning that the problem has been identified more than a 
> year ago. Oh, wait, I've metioned it, sorry :-D
> 
> We really want to make drivers generic enough to be shared by multiple display 
> controllers. I would vote for making the DT bindings generic now already, 
> which would be enough to buy some time to fix the problem properly. If we 
> start prepending driver-specific prefixes such as "omapdss," to compatible 
> string we'll just make the mess even larger and reduce the incentive to fix 
> it. It would be the worst decision we could make.

Well... I think there are no good options here. I see the following options:

1. Add "omapdss," or similar to compat strings in DT, and the same for
the drivers. This solves the issue, but then we'll have bad DT data,
although I see similar method already being used in some places. When we
have common drivers, we can remove the "omapdss," strings from DT, but
we still need to keep them in the drivers to have backward compatibility.

2. Keep the compat strings generic in DT. This way we'll have correct DT
data, but if anyone happens to create a new driver with the same compat
string, things will break. omapdss can only be compiled for a kernel
with OMAP and ARM support, so it narrows the problematic drivers a bit.

3. Have correct DT data, but at init time, in omap arch code, go through
the DT data and change the compat strings for the display nodes to
include "omapdss,". This way the drivers would only work for omap
platforms. Like a combination of 1. and 2. I'm not sure if the DT-code
allows this at the moment, though.

We could also now select option 2., and go for 3. later if someone else
creates a driver with the same compat string.

While I'm obviously not very impartial here, I do think that using
generic bindings for omapdss is not the worst possible case, as:

I'm very much dedicated to get CDF merged at some point, and I already
have been working on it for each revision.

I also think that even if the omap panel drivers are currently omap
specific, they are not very much so. I have been changing them over the
years to be more and more generic, and I have used them as a base for
CDF panel drivers. If some platform specific driver may have a generic
compat string, omap panel drivers are not the worst option.

I will look at the option 3., hopefully that will be possible and
everybody will be happy. Any other ideas appreciated.

 Tomi



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