[PATCH 0/3] drm: Basic mode sanity checks

[Alex Deucher]

On Wed, Dec 17, 2014 at 6:56 AM,  <ville.syrjala at linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> We had a bug in i915 land recently where X passed in a zeroed mode with
> mode_valid=1 to setcrtc. That didn't go down so well and caused a
> div-by-zero in i915.
>
> For a long time I've been thinking that we need some real checks to
> validate the modes we feed into the hardware. I started to sketch out
> something for that but it quickly turned into a bit of a nightmare
> with the whole panel fitter, stereo 3D, SDVO etc. special cases we
> have in i915.
>
> So I gave up on that for now, and instead cooked up this small series
> to add some basic sanity checks to the mode validation, and also apply
> the same sanity checks to user provided modes. This is enough to
> prevent the div-by-zero in i915 with buggy X.
>
> The risk is that we start to reject some modes that more or less worked
> by accident before. Given how lax we've been in handling the panel fitter
> on i915 for instance, this could be a real problem if people have been
> useing custom modes that have been filled out only partially. But I'm
> hoping the number of users doing that is so small that we can risk it.
>
> The other concern is drivers which might also provide funky modes from
> their .get_modes(). I tried to look at all the drivers a bit, and most
> produce modes via EDID, CVT, DMT, or drm_display_mode_from_videomode().
> All of those look safe, except mode->clock might be an issue with
> drm_display_mode_from_videomode(), but hopefully there's some kind of
> clock provided in most cases. I didn't dig through all the nooks and
> crannies in all drivers though, so may have missed something.

For the series:

Reviewed-by: Alex Deucher <alexander.deucher at amd.com>

>
> Ville Syrjälä (3):
>   drm: Reorganize probed mode validation
>   drm: Perform basic sanity checks on probed modes
>   drm: Do basic sanity checks for user modes
>
>  drivers/gpu/drm/drm_crtc.c         |  6 ++++
>  drivers/gpu/drm/drm_modes.c        | 56 ++++++++++++++++++++++++++++++--------
>  drivers/gpu/drm/drm_probe_helper.c | 43 ++++++++++++++---------------
>  include/drm/drm_modes.h            |  6 ++--
>  4 files changed, 74 insertions(+), 37 deletions(-)
>
> --
> 2.0.4
>
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