From: Ville Syrjälä Date: Wed, 23 Feb 2022 13:13:03 +0000 (+0200) Subject: drm/i915: Avoid negative shift due to bigjoiner_pipes==0 X-Git-Tag: howlett/maple/20220722_2~936^2~2^2~5 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=4fe4ed07c815044755075eaad5fe1815436a060f;p=users%2Fjedix%2Flinux-maple.git drm/i915: Avoid negative shift due to bigjoiner_pipes==0 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 Fixes: a6e7a006f5d5 ("drm/i915: Change bigjoiner state tracking to use the pipe bitmask") Signed-off-by: Ville Syrjälä Link: https://patchwork.freedesktop.org/patch/msgid/20220223131315.18016-2-ville.syrjala@linux.intel.com Reviewed-by: Manasi Navare (cherry picked from commit cccc71b552a1040ad3d738d7ec95570801fb0bf6) Signed-off-by: Joonas Lahtinen --- diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c index 80b19c304c43..f3f5f11a5abf 100644 --- a/drivers/gpu/drm/i915/display/intel_display.c +++ b/drivers/gpu/drm/i915/display/intel_display.c @@ -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)