[Openchrome-users] HDMI support clarification

[Xavier Bachelot]

On 04/04/2013 10:45 PM, Amit Uttamchandani wrote:
> On Thu, Apr 04, 2013 at 09:21:55PM +0200, Xavier Bachelot wrote:
> 
> [snip]
> 
>>
>> The X driver contains some support for HDMI output, but it's not very
>> reliable, as you have already found out. As the way forward is KMS and
>> UMS is on the decline, it was better to spend time properly implementing
>> HDMI and DVI support for KMS, that is in the via drm kernel module,
>> rather than fixing the X driver code.
>>
>> So, in some cases, you'll be happy with just the X driver. In other
>> cases, UMS will not work or not properly and then you'll need the
>> drm-openchrome kernel to be able to use KMS.
>>
>> However, the via DRM driver as found in the drm-openchrome kernel is not
>> yet feature complete, and lacks some features that are available with
>> UMS. Most notably, there's no support for 2D acceleration, Xv/XvMC, TV
>> out, etc... Those features will be added over time, and KMS is expected
>> to be on par with UMS and even better in the next few months.
> 
> Currently we are shipping a 3.2.40 kernel with our product. Does the drm
> drivers require code from 3.9 or can I backport the via drm drivers to
> our kernel. Or would you recommend playing around with the X driver and
> trying to get a rudimentary support for HDMI? At this point,
> acceleration is not a concern.
> 
The drm-openchrome kernel is tracking drm-next. It needs to stay close
to upstream kernel in order to be merged when it'll be ready. I'm not
sure how difficult, if at all possible, it would be to backport to an
older kernel.

If what you need is HDMI support and you don't need 2D acceleration,
then I think you'll have a better HDMI support with KMS. However, if you
are tied to a 3.2 kernel, then it might be easier to stick with UMS than
to backport, and thus improve/fix the HDMI support in the X driver,
possibly using information/code from the drm module.

As I said in my previous mail, the focus is now on KMS and UMS will
likely not evolve much, unless someone steps in. However, in middle to
long term, time is probably better spent improving KMS, as the UMS code
is doomed.

Regards,
Xavier