media: venus: firmware: Leave a clue about obtaining CP VARs

The qcom_scm_mem_protect_video_var accepts two sets of <addr size>
pairs as arguments. They describe the virtual address ranges of the
CP (Content Protection) and CP_NONPIXEL regions. It is however not
immediately obvious how to obtain these values.

Leave a comment explaining how one can translate the vendor device
tree properties for use with the mainline driver.
Reviewed-by: Dikshita Agarwal <quic_dikshita@quicinc.com>
Reviewed-by: Vikash Garodia <quic_vgarodia@quicinc.com>
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Stanimir Varbanov <stanimir.k.varbanov@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

drivers/media/platform/qcom/venus/firmware.c

@@ -241,6 +241,16 @@ int venus_boot(struct venus_core *core)
 		return ret;
 
 	if (core->use_tz && res->cp_size) {
+		/*
+		 * Clues for porting using downstream data:
+		 * cp_start = 0
+		 * cp_size = venus_ns/virtual-addr-pool[0] - yes, address and not size!
+		 *   This works, as the non-secure context bank is placed
+		 *   contiguously right after the Content Protection region.
+		 *
+		 * cp_nonpixel_start = venus_sec_non_pixel/virtual-addr-pool[0]
+		 * cp_nonpixel_size = venus_sec_non_pixel/virtual-addr-pool[1]
+		 */
 		ret = qcom_scm_mem_protect_video_var(res->cp_start,
 						     res->cp_size,
 						     res->cp_nonpixel_start,