Re: CDF meeting @FOSDEM report

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

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On 2013-02-06 16:44, Alex Deucher wrote:
> On Wed, Feb 6, 2013 at 6:11 AM, Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:

>> What is an encoder? Something that takes a video signal in, and lets the
>> CPU store the received data to memory? Isn't that a decoder?
>>
>> Or do you mean something that takes a video signal in, and outputs a
>> video signal in another format? (transcoder?)
> 
> In KMS parlance, we have two objects a crtc and an encoder.  A crtc
> reads data from memory and produces a data stream with display timing.
>  The encoder then takes that datastream and timing from the crtc and
> converts it some sort of physical signal (LVDS, TMDS, DP, etc.).  It's

Isn't the video stream between CRTC and encoder just as physical, it
just happens to be inside the GPU?

This is the case for OMAP, at least, where DISPC could be considered
CRTC, and DSI/HDMI/etc could be considered encoder. The stream between
DISPC and DSI/HDMI is plain parallel RGB signal. The video stream could
as well be outside OMAP.

> not always a perfect match to the hardware.  For example a lot of GPUs
> have a DVO encoder which feeds a secondary encoder like an sil164 DVO
> to TMDS encoder.

Right. I think mapping the DRM entities to CDF ones is one of the bigger
question marks we have with CDF. While I'm no expert on DRM, I think we
have the following options:

1. Force DRM's model to CDF, meaning one encoder.

2. Extend DRM to support multiple encoders in a chain.

3. Support multiple encoders in a chain in CDF, but somehow map them to
a single encoder in DRM side.

I really dislike the first option, as it would severely limit where CDF
can be used, or would force you to write some kind of combined drivers,
so that you can have one encoder driver running multiple encoder devices.

 Tomi



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