On Wed, Feb 23, 2022 at 03:13:03PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxx>
> Fixes: a6e7a006f5d5 ("drm/i915: Change bigjoiner state tracking to use the pipe bitmask")
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Reviewed-by: Manasi Navare <manasi.d.navare@xxxxxxxxx>
Manasi
> ---
> drivers/gpu/drm/i915/display/intel_display.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> 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)
> --
> 2.34.1
>
