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drm/i915: Avoid negative shift due to bigjoiner_pipes==0

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bigjoiner_pipes==0 leads bigjoiner_master_pipe() to
do BIT(ffs(0)-1) which is undefined behaviour. The code should
actually still work fine since the only place we provoke
that is intel_crtc_bigjoiner_slave_pipes() and it'll bitwise
AND the result with 0, so doesn't really matter what we get
out of bigjoiner_master_pipe(). But best not provoke undefined
behaviour anyway.

Reported-by: kernel test robot <oliver.sang@intel.com>
Fixes: a6e7a006f5 ("drm/i915: Change bigjoiner state tracking to use the pipe bitmask")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220223131315.18016-2-ville.syrjala@linux.intel.com
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
This commit is contained in:
Ville Syrjälä 2022-02-23 15:13:03 +02:00
parent 53581504a8
commit cccc71b552
1 changed files with 4 additions and 1 deletions
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5
drivers/gpu/drm/i915/display/intel_display.c
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@ -346,7 +346,10 @@ static enum pipe bigjoiner_master_pipe(const struct intel_crtc_state *crtc_state
u8 intel_crtc_bigjoiner_slave_pipes(const struct intel_crtc_state *crtc_state)
{
return crtc_state->bigjoiner_pipes & ~BIT(bigjoiner_master_pipe(crtc_state));
if (crtc_state->bigjoiner_pipes)
return crtc_state->bigjoiner_pipes & ~BIT(bigjoiner_master_pipe(crtc_state));
else
return 0;
}
bool intel_crtc_is_bigjoiner_slave(const struct intel_crtc_state *crtc_state)