Re: [PATCH 1/2] drm/i195: Fix dbuf slice config lookup

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Feb 07, 2022 at 03:26:59PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Apparently I totally fumbled the loop condition when I
> removed the ARRAY_SIZE() stuff from the dbuf slice config
> lookup. Comparing the loop index with the active_pipes bitmask
> is utter nonsense, what we want to do is check to see if the
> mask is zero or not.
> 
> Cc: stable@vger.kernel.org
> Fixes: 05e8155afe35 ("drm/i915: Use a sentinel to terminate the dbuf slice arrays")
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 02084652fe3d..da721aea70ff 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4848,7 +4848,7 @@ static u8 compute_dbuf_slices(enum pipe pipe, u8 active_pipes, bool join_mbus,
>  {
>  	int i;
>  
> -	for (i = 0; i < dbuf_slices[i].active_pipes; i++) {
> +	for (i = 0; dbuf_slices[i].active_pipes != 0; i++) {

Actually looks like the tables just happened to be ordered
the right way that the code never did the wrong thing until
commit eef173954432 ("drm/i915: Allow !join_mbus cases for adlp+
dbuf configuration"). So this just needs backporting alongside
that commit (which I flagged for 5.14+), but no crucial need to
backport further than that.

-- 
Ville Syrjälä
Intel