Re: [Intel-gfx] [PATCH v4 04/16] drm/i915/perf: Determine gen12 oa ctx offset at runtime

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Wed, 12 Oct 2022 15:27:27 -0700, Umesh Nerlige Ramappa wrote:
>
> +static u32 oa_context_image_offset(struct intel_context *ce, u32 reg)
> +{
> +	u32 offset, len = (ce->engine->context_size - PAGE_SIZE) / 4;
> +	u32 *state = ce->lrc_reg_state;
> +
> +	for (offset = 0; offset < len; ) {
> +		if (IS_MI_LRI_CMD(state[offset])) {
> +			/*
> +			 * We expect reg-value pairs in MI_LRI command, so
> +			 * MI_LRI_LEN() should be even, if not, issue a warning.
> +			 */
> +			drm_WARN_ON(&ce->engine->i915->drm,
> +				    MI_LRI_LEN(state[offset]) & 0x1);
> +
> +			if (oa_find_reg_in_lri(state, reg, &offset, len))
> +				break;
> +		} else {
> +			offset++;
> +		}
> +	}
> +
> +	/*
> +	 * Note that the the reg value is written to 'offset + 1' location, so
> +	 * ensure that the offset is less than (len - 1).
> +	 */
> +	return offset < len ? offset : U32_MAX;

Should this then be 'offset < len - 1'? It is actually equivalent since
length is even and we do idx += 2 in oa_find_reg_in_lri so 'offset < len'
is the same as 'offset < len - 1' but since we mention (len - 1) in the
comment maybe clearer to use 'offset < len - 1'?