• Kenneth Graunke's avatar
    drm/i915: Drop support for I915_EXEC_CONSTANTS_* execbuf parameters. · ef0f411f
    Kenneth Graunke authored
    This patch makes the I915_PARAM_HAS_EXEC_CONSTANTS getparam return 0
    (indicating the optional feature is not supported), and makes execbuf
    always return -EINVAL if the flags are used.
    
    Apparently, no userspace ever shipped which used this optional feature:
    I checked the git history of Mesa, xf86-video-intel, libva, and Beignet,
    and there were zero commits showing a use of these flags.  Kernel commit
    72bfa19c apparently introduced the feature prematurely.  According
    to Chris, the intention was to use this in cairo-drm, but "the use was
    broken for gen6", so I don't think it ever happened.
    
    'relative_constants_mode' has always been tracked per-device, but this
    has actually been wrong ever since hardware contexts were introduced, as
    the INSTPM register is saved (and automatically restored) as part of the
    render ring context. The software per-device value could therefore get
    out of sync with the hardware per-context value.  This meant that using
    them is actually unsafe: a client which tried to use them could damage
    the state of other clients, causing the GPU to interpret their BO
    offsets as absolute pointers, leading to bogus memory reads.
    
    These flags were also never ported to execlist mode, making them no-ops
    on Gen9+ (which requires execlists), and Gen8 in the default mode.
    
    On Gen8+, userspace can write these registers directly, achieving the
    same effect.  On Gen6-7.5, it likely makes sense to extend the command
    parser to support them.  I don't think anyone wants this on Gen4-5.
    
    Based on a patch by Dave Gordon.
    
    v3: Return -ENODEV for the getparam, as this is what we do for other
        obsolete features.  Suggested by Chris Wilson.
    
    Cc: stable@vger.kernel.org
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92448Signed-off-by: default avatarKenneth Graunke <kenneth@whitecape.org>
    Reviewed-by: default avatarJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
    Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Link: http://patchwork.freedesktop.org/patch/msgid/20170215093446.21291-1-kenneth@whitecape.orgAcked-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    ef0f411f
i915_drv.c 74.7 KB