Re: [PATCH v8 5/7] drm/i915: keep track of used entries in MOCS table

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Lucas De Marchi (2019-01-22 05:12:25)
> Instead of considering we have defined entries for any index in the
> table, let's keep track of the ones we explicitly defined. This will
> allow Gen 11 to have it's new table defined in which we have holes of
> undefined entries.
> 
> Repeated comments about the meaning of undefined entries were removed
> since they are overly verbose and copy-pasted in several functions: now
> the definition is in the top only.
> 
> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_mocs.c | 88 ++++++++++++++++++++-----------
>  1 file changed, 57 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_mocs.c b/drivers/gpu/drm/i915/intel_mocs.c
> index faae2eefc5cc..af2ae2f396ae 100644
> --- a/drivers/gpu/drm/i915/intel_mocs.c
> +++ b/drivers/gpu/drm/i915/intel_mocs.c
> @@ -28,6 +28,7 @@
>  struct drm_i915_mocs_entry {
>         u32 control_value;
>         u16 l3cc_value;
> +       u16 used;
>  };

> +       /* Set unused values to PTE */
> +       unused_index = I915_MOCS_PTE;
> +
> +       for (i = 0; i < table.size / 2; i++) {
> +               u16 low = table.table[2 * i].used ?
> +                       2 * i : unused_index;
> +               u16 high = table.table[2 * i + 1].used ?
> +                       2 * i + 1 : unused_index;

I'm underwhelmed here.

Could we not do something like

static unsigned int
get_entry_index(struct tbl *tbl, unsigned int idx, unsigned int unused_index)
{
	return tbl->used ? idx : unused_index;
}

		u16 lo = get_entry_index(table.table, 2 * i, unused_index);
		u16 hi = get_entry_index(table.table, 2 * i + 1, unused_index);

That just fits and repeated enough to be worth a little extra effort.
-Chris
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