[Intel-gfx] [PATCH 4/4] drm/i915/perf: add a parameter to control the size of OA buffer

[Chris Wilson]

Quoting Lionel Landwerlin (2018-10-10 17:55:33)
> +static int
> +select_oa_buffer_size(struct drm_i915_private *i915,
> +                     u64 requested_size,
> +                     u32 *selected_size,
> +                     int *selected_exponent)
> +{
> +       const u32 max_size = SZ_16M;
> +
> +       /*
> +        * When no size is specified, use the largest size supported
> +        * by all generations.
> +        */
> +       if (!requested_size) {
> +               *selected_size = SZ_16M;
> +               *selected_exponent = 7;
> +               return 0;
> +       }
> +
> +       /* Start with the smallest OA buffer size. */
> +       *selected_size = 128 * 1024;
> +       *selected_exponent = 0;
> +       while (requested_size > *selected_size &&
> +              *selected_size < max_size) {
> +               *selected_size *= 2;
> +               *selected_exponent += 1;
> +       }
> +
> +       if (requested_size > *selected_size)
> +               return -EINVAL; /* TODO: ENOMEM? ENODEV? */

order = order_base_2(requested_size);
if (order > 24)
	return -EINVAL;
order = max(order, 17);
*selected_size = 1 << order;
*selected_exponent = order - 17;

Returning both is a little redudnant?

return order; (< 0 -> error) ?
-Chris