Re: [PATCH v2] drm/tegra: Add tegra_gem_mmap2 to fix 64-bit offsets

From: Thierry Reding <thierry.reding@gmail.com>
To: Erik Faye-Lund <kusmabite@gmail.com>
Cc: marcheu@chromium.org,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH v2] drm/tegra: Add tegra_gem_mmap2 to fix 64-bit offsets
Date: Fri, 30 Jan 2015 11:21:34 +0100	[thread overview]
Message-ID: <20150130102133.GD16744@ulmo> (raw)
In-Reply-To: <CABPQNSZ5FRBgmYmOacNnLN2oHqjygrA1weZkqPg74k2UNfd=4A@mail.gmail.com>

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On Fri, Jan 30, 2015 at 11:15:30AM +0100, Erik Faye-Lund wrote:
> On Fri, Jan 30, 2015 at 10:49 AM, Thierry Reding
> <thierry.reding@gmail.com> wrote:
> > On Thu, Jan 29, 2015 at 02:18:41PM -0500, Sean Paul wrote:
> >> On 64-bit targets, tegra_gem_mmap doesn't return the
> >> offset to userspace. As such, subsequent calls to mmap(2)
> >> fail. Add a new tegra_gem_mmap2 ioctl to fix this.
> >>
> >> Signed-off-by: Sean Paul <seanpaul@chromium.org>
> >> ---
> >>  drivers/gpu/drm/tegra/drm.c  | 21 +++++++++++++++++++++
> >>  include/uapi/drm/tegra_drm.h |  9 +++++++++
> >>  2 files changed, 30 insertions(+)
> >
> > To be honest, I'd rather just fix the existing IOCTL to do the right
> > thing on 64-bit. All IOCTLs are still protected by the DRM_TEGRA_STAGING
> > Kconfig symbol which depends on STAGING. We originally did that
> > precisely so we'd have some leeway in fixing things up. And we've done
> > precisely that in the past.
> >
> > The only user of this IOCTL is libdrm and I don't think that has any
> > users aside from a few projects that are still under heavy development
> > (like grate or the xf86-video-opentegra driver).
> >
> > Cc'ing Erik, who's probably the only one that's ever worked with this,
> > besides me.
> 
> I also saw the patch, and had the same reaction. I'm fine with
> changing the ABI, it was done already anyway
> (cbfbbabb89b37f6bad05f478d906a385149f288d, "drm/tegra: Remove
> gratuitous pad field"). And as you say, this is only in staging so
> nobody is really relying on it, except grate and libdrm (in which this
> is clearly marked as experimental). I'm fine with just changing it,
> and updating grate and libdrm accordingly.

Okay, I can prepare a patch for libdrm and push it if we decide to go
ahead with this plan.

Rob, Sean, (anyone,) any objections to just changing the ABI? I made
another pass through the list of IOCTL argument structures and couldn't
spot any others that would have the same issue. Perhaps we're finally
approaching a point where we can remove the dependency on STAGING?

Thierry

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