Re: [PATCH 1/2] media: hevc: Remove RPS named flags

[John Cox <jc@kynesim.co.uk>]

>Marking a picture as long-term reference is valid for DPB but not for RPS.
>Change flag name to match with it description in HEVC spec chapiter
>"8.3.2 Decoding process for reference picture set".
>Remove the other unused RPS flags.
>
>Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
>---
> Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst | 6 ++----
> drivers/staging/media/hantro/hantro_g2_hevc_dec.c         | 2 +-
> drivers/staging/media/sunxi/cedrus/cedrus_h265.c          | 2 +-
> include/media/hevc-ctrls.h                                | 4 +---
> 4 files changed, 5 insertions(+), 9 deletions(-)
>
>diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>index 3865acb9e0fd..eff33c511090 100644
>--- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>+++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>@@ -3138,10 +3138,8 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
> 	:c:type:`timeval` in struct :c:type:`v4l2_buffer` to a __u64.
>     * - __u8
>       - ``rps``
>-      - The reference set for the reference frame
>-        (V4L2_HEVC_DPB_ENTRY_RPS_ST_CURR_BEFORE,
>-        V4L2_HEVC_DPB_ENTRY_RPS_ST_CURR_AFTER or
>-        V4L2_HEVC_DPB_ENTRY_RPS_LT_CURR)
>+      - Long term flag for the reference frame
>+        (V4L2_HEVC_DPB_ENTRY_LONG_TERM_REFERENCE)
>     * - __u8
>       - ``field_pic``
>       - Whether the reference is a field picture or a frame.

If you are going to remove all the RPS values except for Long Term
wouldn't it be better to rename the field too, either to "flags" or a
bool "is_long_term"?  If we have a field called RPS it really should be
able to have a value for any of the 5 valid Reference Picture Sets that
a DPB entry can belong to.

As a side note, it is important to my code that the DPB array contains
all the DPB entries not just the ones that are in use in this frame.  I
need them so I can track which frames have left the DPB so I can
reuse/free the MV tables associated with them (yes I could keep one for
every entry in the capture Q but that is generally wasteful on memory
and the Pi is often memory constrained). So maybe update the docn on DPB
to make this explicit please? (I suspect that current code does this
anyway as it is generally easier to do than to not.)

John Cox

>diff --git a/drivers/staging/media/hantro/hantro_g2_hevc_dec.c b/drivers/staging/media/hantro/hantro_g2_hevc_dec.c
>index 9ea864ca5625..be46b3c28b17 100644
>--- a/drivers/staging/media/hantro/hantro_g2_hevc_dec.c
>+++ b/drivers/staging/media/hantro/hantro_g2_hevc_dec.c
>@@ -503,7 +503,7 @@ static int set_ref(struct hantro_ctx *ctx)
> 		compress_luma_addr = luma_addr + compress_luma_offset;
> 		compress_chroma_addr = luma_addr + compress_chroma_offset;
> 
>-		if (dpb[i].rps == V4L2_HEVC_DPB_ENTRY_RPS_LT_CURR)
>+		if (dpb[i].rps == V4L2_HEVC_DPB_ENTRY_LONG_TERM_REFERENCE)
> 			dpb_longterm_e |= BIT(V4L2_HEVC_DPB_ENTRIES_NUM_MAX - 1 - i);
> 
> 		/*
>diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h265.c b/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
>index ef0311a16d01..6086cc35e8cc 100644
>--- a/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
>+++ b/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
>@@ -169,7 +169,7 @@ static void cedrus_h265_ref_pic_list_write(struct cedrus_dev *dev,
> 		unsigned int index = list[i];
> 		u8 value = list[i];
> 
>-		if (dpb[index].rps == V4L2_HEVC_DPB_ENTRY_RPS_LT_CURR)
>+		if (dpb[index].rps == V4L2_HEVC_DPB_ENTRY_LONG_TERM_REFERENCE)
> 			value |= VE_DEC_H265_SRAM_REF_PIC_LIST_LT_REF;
> 
> 		/* Each SRAM word gathers up to 4 references. */
>diff --git a/include/media/hevc-ctrls.h b/include/media/hevc-ctrls.h
>index ef63bc205756..f587448ef495 100644
>--- a/include/media/hevc-ctrls.h
>+++ b/include/media/hevc-ctrls.h
>@@ -127,9 +127,7 @@ struct v4l2_ctrl_hevc_pps {
> 	__u64	flags;
> };
> 
>-#define V4L2_HEVC_DPB_ENTRY_RPS_ST_CURR_BEFORE	0x01
>-#define V4L2_HEVC_DPB_ENTRY_RPS_ST_CURR_AFTER	0x02
>-#define V4L2_HEVC_DPB_ENTRY_RPS_LT_CURR		0x03
>+#define V4L2_HEVC_DPB_ENTRY_LONG_TERM_REFERENCE	0x01
> 
> #define V4L2_HEVC_DPB_ENTRIES_NUM_MAX		16
>