[Mesa-dev] Drooping multiple driver support in EGL?

[Jose Fonseca]

----- Original Message -----
> On 01/12/2012 09:06 AM, Chia-I Wu wrote:
> > On Tue, Jan 10, 2012 at 12:55 AM, Jose Fonseca<jfonseca at vmware.com>
> >  wrote:
> >>
> >>
> >> ----- Original Message -----
> >>> On Fri, Dec 23, 2011 at 7:51 PM, Chia-I Wu<olvaffe at gmail.com>
> >>>  wrote:
> >>>> On Sat, Dec 24, 2011 at 12:37 AM, Ian Romanick
> >>>> <idr at freedesktop.org>  wrote:
> >>>>> On 12/23/2011 07:20 AM, Jose Fonseca wrote:
> >>>>>>
> >>>>>> ----- Original Message -----
> >>>>>>>
> >>>>>>> Hi list,
> >>>>>>>
> >>>>>>> Multiple driver support in EGL is hard to get right, if not
> >>>>>>> impossible.
> >>>>>>> On Linux desktop, we almost always want to use egl_dri2.  It
> >>>>>>> allows
> >>>>>>> EGL
> >>>>>>> to loads DRI2 drivers, thus allowing it to share DRI2 drivers
> >>>>>>> with
> >>>>>>> libGL.
> >>>>>>>
> >>>>>>> In one case where the app wants to use OpenVG, libEGL needs
> >>>>>>> to
> >>>>>>> load
> >>>>>>> egl_gallium instead.  The problem comes from that we cannot
> >>>>>>> know
> >>>>>>> that
> >>>>>>> an
> >>>>>>> OpenVG context is to be created until it is created.  But
> >>>>>>> before
> >>>>>>> a
> >>>>>>> context can be created, EGL needs to be initialized and an
> >>>>>>> EGLConfig
> >>>>>>> needs to be chosen.  So when EGL is to be initialized, we
> >>>>>>> need
> >>>>>>> to
> >>>>>>> load
> >>>>>>> and initilaize all EGL drivers.  When an EGLConfig is to be
> >>>>>>> picked,
> >>>>>>> we
> >>>>>>> need to pick it from all drivers.
> >>>>>>
> >>>>>>
> >>>>>> Couldn't we restructure this such that OpenVG (and all other
> >>>>>> state
> >>>>>> trackers on Linux) still use a dri2 driver, but one which
> >>>>>> exposes
> >>>>>> an
> >>>>>> additional (gallium specific) interface?
> >>>>> I was going to suggest something similar.  I think we want
> >>>>> fewer
> >>>>> EGL
> >>>>> backends to test and maintain, not more.  Right?
> >>>> I totally agree with that.  I even had an unfinished branch for
> >>>> that.
> >>>>
> >>>> Note that this thread is about dropping multiple EGL driver
> >>>> support.
> >>>> The motivation for having OpenVG in DRI2 drivers is that we do
> >>>> not
> >>>> want multiple EGL drivers.  The former should push the latter to
> >>>> happen more quickly, instead of preventing it from happening.
> >>>
> >>> The problem with exposing the Gallium Interface via the DRI
> >>> interface
> >>> is that the DRI interface is public and stable while the Gallium
> >>> one
> >>> is
> >>> not.
> >>
> >> I think one doesn't invalidate the other. That is, it is
> >> technically feasible to have an unstable interface on top of an
> >> stable interface. In detail, we could add a stable extension DRI ,
> >> which exposes Gallium (eg. DRI2GetGalliumScreen). Obviously, for
> >> things to work, it would be imperative that the libEGL.so and
> >> foo_dri.so were built together, which is already the case today.
> 
> We don't get to require that lib*GL and *_dri.so be upgraded in
> lock-step.  Ever.

I'm afraid I don't understand what you're trying to say.. (Who requires what and why?)


Anyway, the fact is that gallium state tracker and pipe driver have to be upgraded in lock-step *today*, and my point is that it must be somehow possible to preserve that constraint, without having to do something completely different from the non-gallium drivers.

Jose