Re: [PATCH v3 1/7] drm: Add DSI bus infrastructure

[Thierry Reding <thierry.reding@gmail.com>]

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On Thu, Nov 14, 2013 at 03:15:57PM +0100, Andrzej Hajda wrote:
> Hi Thierry,
> 
> On 11/13/2013 10:38 PM, Thierry Reding wrote:
> > On Tue, Nov 12, 2013 at 03:14:22PM +0100, Andrzej Hajda wrote:
> >> Hi Thierry,
> >>
> >> I have already sent patch with DSI bus implementation [1].
> >> It was posted as the first step of CDF implementation attempt,
> >> but in fact it do not depend on CDF.
> >>
> >> [1]
> >> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg45252.html
> > Seems like that patchset was never merged. I guess probably because it
> > was posted as part of CDF work.
> >
> > Do you have any plans on continuing work on that?If not I could extract
> > the DSI bus patch from the series, it's largely similar to the patch I
> > proposed here, and rework it somewhat.
> I will soon sent new patch with the current version of the bus.
> It could be a better base to your rework.

Any estimate on when this will be? I want to get started on this as soon
as possible so we can get this in good shape for 3.14. I suspect that if
I start based on the current patch, I won't have to redo everything when
updating for the next version. Quite a bit should remain similar, right?

> > I'd very much like to avoid
> > putting the code in drivers/video, though, since that's considered
> > obsolete.
> I have followed convention proposed by Laurent in his DBI bus.
> It seems to me OK - DSI bus is more related to video than to drm.
> I know that drivers/video is mostly occupied by FB drivers,
> but according to Kconfig it is not only for FB.
> Of course this is only my suggestion.

I've had an IRC discussion with Dave and Rob (added on Cc), and they
both agreed that implementing it as part of DRM would be preferred.

The reason, as I've said before, is primarily that drivers/video is
considered obsolete and new drivers and features should be implemented
within the context of DRM/KMS. Additionally this has the benefit of
being able to reuse the native DRM data structures and types, as well as
helper functions, without having to go through an extra layer of
compatibility.

> >  Furthermore I think if we kept the transfer function proposed
> > in my patch should make it easier to address Bert's comments from your
> > posting.
> I am not sure which part of Barts comment you are addressing.
> Anyway I also prefer passing struct and returning ssize_t.
> I am not sure about splitting type and channel but this seems to be a
> minor detail.

I find that to be a perfectly natural split. A DSI peripheral will have
an associated virtual channel number anyway, and having a separate field
will allow drivers to just copy that field into the dsi_msg's
equivalent.

The alternative would be to require each driver to properly encode the
channel and data type.

Thierry

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