linux-kernel - Re: [PATCH 1/3] drm: add gem ttm helpers

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Message-ID: <20190807103649.aedmac63eop6ktlk@sirius.home.kraxel.org>
Date:   Wed, 7 Aug 2019 12:36:49 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] drm: add gem ttm helpers

  Hi,

> > > Same for this, you're just upcasting to ttm_bo and then downcasting to
> > > gem_bo again ... I think just a series to roll out the existing gem
> > > helpers everywhere should work?
> >
> > I don't think so.  drm_gem_dumb_map_offset() calls
> > drm_gem_create_mmap_offset(), which I think is not correct for ttm
> > objects because ttm_bo_init() handles vma_node initialization.
> 
> More code to unify first? This should work exactly the same way for
> all gem based drivers I think ... Only tricky bit is making sure
> vmwgfx keeps working correctly.

Yea.  Unifying on the gem way of doing things isn't going to work very
well.  We would have to keep the current way of doing things in the ttm
code, wrapped into "if (ttm_bo_uses_embedded_gem_object()) { ... }", to
not break vmwgfx.

So adding gem ttm helpers (where gem+ttm drivers can opt-in) looked like
the better way of handling this to me ...

cheers,
  Gerd