Re: [PATCH 0/4] Enable Hantro G1 post-processor

[Nicolas Dufresne <nicolas@ndufresne.ca>]

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Le mercredi 11 septembre 2019 à 09:27 +0100, Ezequiel Garcia a écrit :
> On Mon, 2019-09-09 at 16:07 +0900, Tomasz Figa wrote:
> > Hi Ezequiel,
> > 
> > On Wed, Sep 4, 2019 at 3:17 AM Ezequiel Garcia <ezequiel@collabora.com> wrote:
> > > Hi all,
> > > 
> > > This series enables the post-processor support available
> > > on the Hantro G1 VPU. The post-processor block can be
> > > pipelined with the decoder hardware, allowing to perform
> > > operations such as color conversion, scaling, rotation,
> > > cropping, among others.
> > > 
> > > The decoder hardware needs its own set of NV12 buffers
> > > (the native decoder format), and the post-processor is the
> > > owner of the CAPTURE buffers. This allows the application
> > > get processed (scaled, converted, etc) buffers, completely
> > > transparently.
> > > 
> > > This feature is implemented by exposing other CAPTURE pixel
> > > formats to the application (ENUM_FMT). When the application
> > > sets a pixel format other than NV12, the driver will enable
> > > and use the post-processor transparently.
> > 
> > I'll try to review the series a bit later, but a general comment here
> > is that the userspace wouldn't have a way to distinguish between the
> > native and post-processed formats. I'm pretty much sure that
> > post-processing at least imposes some power penalty, so it would be
> > good if the userspace could avoid it if unnecessary.
> > 
> 
> Hm, that's true, good catch.
> 
> So, it would be desirable to retain the current behavior of allowing
> the application to just set a different pixel format and get
> a post-processed frame, transparently.
> 
> But at the same time, it would be nice if the application is somehow
> aware of the post-processing happening. Maybe we can expose a more
> accurate media controller topology, have applications enable
> the post-processing pipeline explicitly.

How it works on the stateful side is that userspace set the encoding
type (the codec), then passes a header (in our case, there will be
parsed structures replacing this) first. The driver then configure
capture format, giving a hint of the "default" or "native" format. This
may or may not be sufficient, but it does work in giving userspace a
hint.

> 
> Thanks for the feedback,
> Ezequiel
> 

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