Re: [EXT] [PATCH 1/5] media: add v4l2 JPEG helpers

[Mirela Rabulea <mirela.rabulea@nxp.com>]

Hi Philipp,
I tried using these helpers for imx8 jpeg encoder/decoder, and the main
issues that I have are:
1. It is necessary to support ARGB (4 components)
2. It is necessary to support extended sequential (parse SOF1)
3. It is necessary to distinguish somehow between YUV and RGB, I used
APP14 marker to do that
4. It is necessary to be able to modify/patch the component ID's inside
SOF & SOS segments; this is due to a hardware limitation that the
component ID's must be 0..3 or 1..4, however it is possible to decode a
jpeg that violates this condition, if the component ID's are patched to
accepted values.

I have a concern related to performance, about parsing the jpeg like
that, but I did not get to measure anything yet, as I could not fully
integrate imx8 jpeg driver with the helpers, I
used v4l2_jpeg_parse_header, but I also had to keep my old structures.
Please take a look in my imx8 patch, at mxc-jpeg.h, struct
mxc_jpeg_sof/struct mxc_jpeg_sos, these are __packed structures, they
work quite well via a simple cast and allow modifications too, the
downside is that fields bigger than u8 might require swapping. 

Please also see below my comments.

On Mi, 2019-11-13 at 16:05 +0100, Philipp Zabel wrote:
> Add helpers for JPEG header parsing. They allow both scanning for
> marker
> segment positions and later parsing the segments individually, as
> required by s5p-jpeg, as well as parsing all headers in one go, as
> required by coda-vpu. The frame header is always parsed, as basically
> all decoders are interested in width, height, and number of
> components.
> For convenience, the JPEG chroma subsampling factors are decoded into
> a
> v4l2_jpeg_chroma_subsampling enum.
> 
> Only baseline DCT encoded JPEGs with 8-bit precision and either
> grayscale (1 component) or YCbCr (3 components) encodings are
> supported,
> as current drivers do not support different formats.

For imx8 jpeg enc/dec, there is a 4-component format that should be 
supported, ARGB.
Also, extended sequential DCF should be supported.

> 
> Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
> ---
>  drivers/media/v4l2-core/Kconfig     |   4 +
>  drivers/media/v4l2-core/Makefile    |   2 +
>  drivers/media/v4l2-core/v4l2-jpeg.c | 614
> ++++++++++++++++++++++++++++
>  include/media/v4l2-jpeg.h           | 135 ++++++
>  4 files changed, 755 insertions(+)
>  create mode 100644 drivers/media/v4l2-core/v4l2-jpeg.c
>  create mode 100644 include/media/v4l2-jpeg.h
> 
> diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-
> core/Kconfig
> index 39e3fb30ba0b..89809ec24779 100644
> --- a/drivers/media/v4l2-core/Kconfig
> +++ b/drivers/media/v4l2-core/Kconfig
> @@ -45,6 +45,10 @@ config VIDEO_PCI_SKELETON
>  config VIDEO_TUNER
>         tristate
> 
> +# Used by drivers that need v4l2-jpeg.ko
> +config V4L2_JPEG_HELPER
> +       tristate
> +
>  # Used by drivers that need v4l2-mem2mem.ko
>  config V4L2_MEM2MEM_DEV
>         tristate
> diff --git a/drivers/media/v4l2-core/Makefile b/drivers/media/v4l2-
> core/Makefile
> index 786bd1ec4d1b..144564656d22 100644
> --- a/drivers/media/v4l2-core/Makefile
> +++ b/drivers/media/v4l2-core/Makefile
> @@ -24,6 +24,8 @@ obj-$(CONFIG_V4L2_MEM2MEM_DEV) += v4l2-mem2mem.o
> 
>  obj-$(CONFIG_V4L2_FLASH_LED_CLASS) += v4l2-flash-led-class.o
> 
> +obj-$(CONFIG_V4L2_JPEG_HELPER) += v4l2-jpeg.o
> +
>  obj-$(CONFIG_VIDEOBUF_GEN) += videobuf-core.o
>  obj-$(CONFIG_VIDEOBUF_DMA_SG) += videobuf-dma-sg.o
>  obj-$(CONFIG_VIDEOBUF_DMA_CONTIG) += videobuf-dma-contig.o
> diff --git a/drivers/media/v4l2-core/v4l2-jpeg.c
> b/drivers/media/v4l2-core/v4l2-jpeg.c
> new file mode 100644
> index 000000000000..f1e1a818b47c
> --- /dev/null
> +++ b/drivers/media/v4l2-core/v4l2-jpeg.c
> @@ -0,0 +1,614 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * V4L2 JPEG header parser helpers.
> + *
> + * Copyright (C) 2019 Pengutronix, Philipp Zabel <kernel@pengutronix
> .de>
> + *
> + * For reference, see JPEG ITU-T.81 (ISO/IEC 10918-1) [1]
> + *
> + * [1] https://eur01.safelinks.protection.outlook.com/?url=https%3A%
> 2F%2Fwww.w3.org%2FGraphics%2FJPEG%2Fitu-
> t81.pdf&amp;data=02%7C01%7Cmirela.rabulea%40nxp.com%7C956e2804c0cb4b1
> 115e508d7684b015d%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637092
> 543660676373&amp;sdata=ucUFNyEMiBRtd9syRPy22RBEikoPsve7j%2BtB%2FtEn%2
> FQU%3D&amp;reserved=0
> + */
> +
> +#include <asm/unaligned.h>
> +#include <linux/errno.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/types.h>
> +#include <media/v4l2-jpeg.h>
> +
> +MODULE_DESCRIPTION("V4L2 JPEG header parser helpers");
> +MODULE_AUTHOR("Philipp Zabel <kernel@pengutronix.de>");
> +MODULE_LICENSE("GPL");
> +
> +/* Table B.1 - Marker code assignments */
> +#define SOF0   0xffc0  /* start of frame */
> +#define SOF1   0xffc1
> +#define SOF3   0xffc3
> +#define SOF5   0xffc5
> +#define SOF7   0xffc7
> +#define JPG    0xffc8  /* extensions */
> +#define SOF9   0xffc9
> +#define SOF11  0xffcb
> +#define SOF13  0xffcd
> +#define SOF15  0xffcf
> +#define DHT    0xffc4  /* huffman table */
> +#define DAC    0xffcc  /* arithmetic coding conditioning */
> +#define RST0   0xffd0  /* restart */
> +#define RST7   0xffd7
> +#define SOI    0xffd8  /* start of image */
> +#define EOI    0xffd9  /* end of image */
> +#define SOS    0xffda  /* start of stream */
> +#define DQT    0xffdb  /* quantization table */
> +#define DNL    0xffdc  /* number of lines */
> +#define DRI    0xffdd  /* restart interval */
> +#define DHP    0xffde  /* hierarchical progression */
> +#define EXP    0xffdf  /* expand reference */
> +#define APP0   0xffe0  /* application data */

APP14 would be nice to have.

> +#define APP15  0xffef
> +#define JPG0   0xfff0  /* extensions */
> +#define JPG13  0xfffd
> +#define COM    0xfffe  /* comment */
> +#define TEM    0xff01  /* temporary */
> +
> +/**
> + * struct jpeg_stream - JPEG byte stream
> + * @curr: current position in stream
> + * @end: end position, after last byte
> + */
> +struct jpeg_stream {
> +       u8 *curr;
> +       u8 *end;
> +};
> +
> +/* returns a value that fits into u8, or negative error */
> +static int jpeg_get_byte(struct jpeg_stream *stream)
> +{
> +       if (stream->curr >= stream->end)
> +               return -EINVAL;
> +
> +       return *stream->curr++;
> +}
> +
> +/* returns a value that fits into u16, or negative error */
> +static int jpeg_get_word_be(struct jpeg_stream *stream)
> +{
> +       u16 word;
> +
> +       if (stream->curr + sizeof(__be16) > stream->end)
> +               return -EINVAL;
> +
> +       word = get_unaligned_be16(stream->curr);
> +       stream->curr += sizeof(__be16);
> +
> +       return word;
> +}
> +
> +static int jpeg_skip(struct jpeg_stream *stream, size_t len)
> +{
> +       if (stream->curr + len > stream->end)
> +               return -EINVAL;
> +
> +       stream->curr += len;
> +
> +       return 0;
> +}
> +
> +static int jpeg_next_marker(struct jpeg_stream *stream)
> +{
> +       int byte;
> +       u16 marker = 0;
> +
> +       while ((byte = jpeg_get_byte(stream)) >= 0) {
> +               marker = (marker << 8) | byte;
> +               /* skip stuffing bytes and REServed markers */
> +               if (marker == TEM || (marker > 0xffbf && marker <
> 0xffff))
> +                       return marker;
> +       }
> +
> +       return byte;
> +}
> +
> +/* this does not advance the current position in the stream */
> +static int jpeg_reference_segment(struct jpeg_stream *stream,
> +                                 struct v4l2_jpeg_reference
> *segment)
> +{
> +       u16 len;
> +
> +       if (stream->curr + sizeof(__be16) > stream->end)
> +               return -EINVAL;
> +
> +       len = get_unaligned_be16(stream->curr);
> +       if (stream->curr + len > stream->end)
> +               return -EINVAL;
> +
> +       segment->start = stream->curr;
> +       segment->length = len;
> +
> +       return 0;
> +}
> +
> +static int v4l2_jpeg_decode_subsampling(u8 nf, u8 h_v)
> +{
> +       if (nf == 1)
> +               return V4L2_JPEG_CHROMA_SUBSAMPLING_GRAY;
> +
> +       switch (h_v) {
> +       case 0x11:
> +               return V4L2_JPEG_CHROMA_SUBSAMPLING_444;
> +       case 0x21:
> +               return V4L2_JPEG_CHROMA_SUBSAMPLING_422;
> +       case 0x22:
> +               return V4L2_JPEG_CHROMA_SUBSAMPLING_420;
> +       case 0x41:
> +               return V4L2_JPEG_CHROMA_SUBSAMPLING_411;
> +       default:
> +               return -EINVAL;
> +       }
> +}
> +
> +static int jpeg_parse_frame_header(struct jpeg_stream *stream,
> +                                  struct v4l2_jpeg_frame_header
> *frame_header)
> +{
> +       int len = jpeg_get_word_be(stream);
> +
> +       if (len < 0)
> +               return len;
> +       /* Lf = 8 + 3 * Nf, Nf >= 1 */
> +       if (len < 8 + 3)
> +               return -EINVAL;
> +
> +       if (frame_header) {
> +               /* Table B.2 - Frame header parameter sizes and
> values */
> +               int p, y, x, nf;
> +               int i;
> +
> +               p = jpeg_get_byte(stream);
> +               if (p < 0)
> +                       return p;
> +               /* baseline DCT only supports 8-bit precision */
> +               if (p != 8)
> +                       return -EINVAL;
> +
> +               y = jpeg_get_word_be(stream);
> +               if (y < 0)
> +                       return y;
> +               if (y == 0)
> +                       return -EINVAL;
> +
> +               x = jpeg_get_word_be(stream);
> +               if (x < 0)
> +                       return x;
> +               if (x == 0)
> +                       return -EINVAL;
> +
> +               nf = jpeg_get_byte(stream);
> +               if (nf < 0)
> +                       return nf;
> +               /*
> +                * The spec allows 1 <= Nf <= 255, but we only
> support YCbCr
> +                * and grayscale.
> +                */
> +               if (nf != 1 && nf != 3)

This will be a problem for ARGB (4 components)

> +                       return -EINVAL;
> +               if (len != 8 + 3 * nf)
> +                       return -EINVAL;
> +
> +               frame_header->precision = p;
> +               frame_header->height = y;
> +               frame_header->width = x;
> +               frame_header->num_components = nf;
> +
> +               for (i = 0; i < nf; i++) {
> +                       struct v4l2_jpeg_frame_component_spec
> *component;
> +                       int c, h_v, tq;
> +
> +                       c = jpeg_get_byte(stream);
> +                       if (c < 0)
> +                               return c;
> +
> +                       h_v = jpeg_get_byte(stream);
> +                       if (h_v < 0)
> +                               return h_v;
> +                       if (i == 0) {
> +                               int subs;
> +
> +                               subs =
> v4l2_jpeg_decode_subsampling(nf, h_v);
> +                               if (subs < 0)
> +                                       return subs;
> +                               frame_header->subsampling = subs;
> +                       } else if (h_v != 0x11) {
> +                               /* all chroma sampling factors must
> be 1 */
> +                               return -EINVAL;
> +                       }
> +
> +                       tq = jpeg_get_byte(stream);
> +                       if (tq < 0)
> +                               return tq;
> +
> +                       component = &frame_header->component[i];
> +                       component->component_identifier = c;
> +                       component->horizontal_sampling_factor =
> +                               (h_v >> 4) & 0xf;
> +                       component->vertical_sampling_factor = h_v &
> 0xf;
> +                       component->quantization_table_selector = tq;
> +               }
> +       } else {
> +               return jpeg_skip(stream, len - 2);
> +       }
> +
> +       return 0;
> +}
> +
> +static int jpeg_parse_scan_header(struct jpeg_stream *stream,
> +                                 struct v4l2_jpeg_scan_header
> *scan_header)
> +{
> +       size_t skip;
> +       int len = jpeg_get_word_be(stream);
> +
> +       if (len < 0)
> +               return len;
> +       /* Ls = 8 + 3 * Ns, Ns >= 1 */
> +       if (len < 6 + 2)
> +               return -EINVAL;
> +
> +       if (scan_header) {
> +               int ns;
> +               int i;
> +
> +               ns = jpeg_get_byte(stream);
> +               if (ns < 0)
> +                       return ns;
> +               if (ns < 1 || ns > 4 || len != 6 + 2 * ns)
> +                       return -EINVAL;
> +
> +               scan_header->num_components = ns;
> +
> +               for (i = 0; i < ns; i++) {
> +                       struct v4l2_jpeg_scan_component_spec
> *component;
> +                       int cs, td_ta;
> +
> +                       cs = jpeg_get_byte(stream);
> +                       if (cs < 0)
> +                               return cs;
> +
> +                       td_ta = jpeg_get_byte(stream);
> +                       if (td_ta < 0)
> +                               return td_ta;
> +
> +                       component = &scan_header->component[i];
> +                       component->component_selector = cs;
> +                       component->dc_entropy_coding_table_selector =
> +                               (td_ta >> 4) & 0xf;
> +                       component->ac_entropy_coding_table_selector =
> +                               td_ta & 0xf;
> +               }
> +
> +               skip = 3; /* skip Ss, Se, Ah, and Al */
> +       } else {
> +               skip = len - 2;
> +       }
> +
> +       return jpeg_skip(stream, skip);
> +}
> +
> +/* B.2.4.1 Quantization table-specification syntax */
> +static int jpeg_parse_quantization_tables(struct jpeg_stream
> *stream,
> +                                         struct v4l2_jpeg_reference
> *tables)
> +{
> +       int len = jpeg_get_word_be(stream);
> +
> +       if (len < 0)
> +               return len;
> +       /* Lq = 2 + n * 65 (for baseline DCT), n >= 1 */
> +       if (len < 2 + 65)
> +               return -EINVAL;
> +
> +       for (len -= 2; len >= 65; len -= 65) {
> +               u8 pq, tq, *qk;
> +               int ret;
> +               int pq_tq = jpeg_get_byte(stream);
> +
> +               if (pq_tq < 0)
> +                       return pq_tq;
> +
> +               /* quantization table element precision */
> +               pq = (pq_tq >> 4) & 0xf;
> +               /* only 8-bit Qk values for baseline DCT */
> +               if (pq != 0)
> +                       return -EINVAL;
> +
> +               /* quantization table destination identifier */
> +               tq = pq_tq & 0xf;
> +               if (tq > 3)
> +                       return -EINVAL;
> +
> +               /* quantization table element */
> +               qk = stream->curr;
> +               ret = jpeg_skip(stream, 64);
> +               if (ret < 0)
> +                       return -EINVAL;
> +
> +               if (tables) {
> +                       tables[tq].start = qk;
> +                       tables[tq].length = 64;
> +               }
> +       }
> +
> +       return 0;
> +}
> +
> +/* B.2.4.2 Huffman table-specification syntax */
> +static int jpeg_parse_huffman_tables(struct jpeg_stream *stream,
> +                                    struct v4l2_jpeg_reference
> *tables)
> +{
> +       int mt;
> +       int len = jpeg_get_word_be(stream);
> +
> +       if (len < 0)
> +               return len;
> +       /* Table B.5 - Huffman table specification parameter sizes
> and values */
> +       if (len < 2 + 17)
> +               return -EINVAL;
> +
> +       for (len -= 2; len >= 17; len -= 17 + mt) {
> +               u8 tc, th, *table;
> +               int tc_th = jpeg_get_byte(stream);
> +               int i, ret;
> +
> +               if (tc_th < 0)
> +                       return tc_th;
> +
> +               /* table class - 0 = DC, 1 = AC */
> +               tc = (tc_th >> 4) & 0xf;
> +               if (tc > 1)
> +                       return -EINVAL;
> +
> +               /* huffman table destination identifier */
> +               th = tc_th & 0xf;
> +               /* only two Huffman tables for baseline DCT */
> +               if (th > 1)
> +                       return -EINVAL;
> +
> +               /* BITS - number of Huffman codes with length i */
> +               table = stream->curr;
> +               mt = 0;
> +               for (i = 0; i < 16; i++) {
> +                       int li;
> +
> +                       li = jpeg_get_byte(stream);
> +                       if (li < 0)
> +                               return li;
> +
> +                       mt += li;
> +               }
> +               /* HUFFVAL - values associated with each Huffman code
> */
> +               ret = jpeg_skip(stream, mt);
> +               if (ret < 0)
> +                       return ret;
> +
> +               if (tables) {
> +                       tables[(tc << 1) | th].start = table;
> +                       tables[(tc << 1) | th].length = stream->curr
> - table;
> +               }
> +       }
> +
> +       return jpeg_skip(stream, len - 2);
> +}
> +
> +/* B.2.4.4 Restart interval definition syntax */
> +static int jpeg_parse_restart_interval(struct jpeg_stream *stream,
> +                                      u16 *restart_interval)
> +{
> +       int len = jpeg_get_word_be(stream);
> +       int ri;
> +
> +       if (len < 0)
> +               return len;
> +       if (len != 4)
> +               return -EINVAL;
> +
> +       ri = jpeg_get_word_be(stream);
> +       if (ri < 0)
> +               return ri;
> +
> +       *restart_interval = ri;
> +
> +       return 0;
> +}
> +
> +static int jpeg_skip_segment(struct jpeg_stream *stream)
> +{
> +       int len = jpeg_get_word_be(stream);
> +
> +       if (len < 0)
> +               return len;
> +       if (len < 2)
> +               return -EINVAL;
> +
> +       return jpeg_skip(stream, len - 2);
> +}
> +
> +/**
> + * jpeg_parse_header - locate marker segments and optionally parse
> headers
> + * @buf: address of the JPEG buffer, should start with a SOI marker
> + * @len: length of the JPEG buffer
> + * @out: returns marker segment positions and optionally parsed
> headers
> + *
> + * The out->scan_header pointer must be initialized to NULL or point
> to a valid
> + * v4l2_jpeg_scan_header structure. The out->huffman_tables and
> + * out->quantization_tables pointers must be initialized to NULL or
> point to a
> + * valid array of 4 v4l2_jpeg_reference structures each.
> + *
> + * Returns 0 or negative error if parsing failed.
> + */
> +int v4l2_jpeg_parse_header(void *buf, size_t len, struct
> v4l2_jpeg_header *out)
> +{
> +       struct jpeg_stream stream;
> +       int marker;
> +       int ret = 0;
> +
> +       stream.curr = buf;
> +       stream.end = stream.curr + len;
> +
> +       out->num_dht = 0;
> +       out->num_dqt = 0;
> +
> +       /* the first marker must be SOI */
> +       marker = jpeg_next_marker(&stream);
> +       if (marker < 0)
> +               return marker;
> +       if (marker != SOI)
> +               return -EINVAL;
> +
> +       /* loop through marker segments */
> +       while ((marker = jpeg_next_marker(&stream)) >= 0) {
> +               switch (marker) {
> +               /* baseline DCT */
> +               case SOF0:
For imx8 jpeg, extended sequential should be supported. Adding the SOF1
here would help, but maybe other changes are needed too.
> +                       ret = jpeg_reference_segment(&stream, &out-
> >sof);
> +                       if (ret < 0)
> +                               return ret;
> +                       ret = jpeg_parse_frame_header(&stream, &out-
> >frame);
> +                       break;
> +               /* extended sequential, progressive, lossless */
> +               case SOF1 ... SOF3:
> +               /* differential coding */
> +               case SOF5 ... SOF7:
> +               /* arithmetic coding */
> +               case SOF9 ... SOF11:
> +               case SOF13 ... SOF15:
> +                       /* fallthrough */
> +               case DAC:
> +               case TEM:
> +                       return -EINVAL;
> +
> +               case DHT:
> +                       ret = jpeg_reference_segment(&stream,
> +                                       &out->dht[out->num_dht++ %
> 4]);
> +                       if (ret < 0)
> +                               return ret;
> +                       ret = jpeg_parse_huffman_tables(&stream,
> +                                                       out-
> >huffman_tables);
> +                       break;
> +               case DQT:
> +                       ret = jpeg_reference_segment(&stream,
> +                                       &out->dqt[out->num_dqt++ %
> 4]);
> +                       if (ret < 0)
> +                               return ret;
> +                       ret = jpeg_parse_quantization_tables(&stream,
> +                                       out->quantization_tables);
> +                       break;
> +               case DRI:
> +                       ret = jpeg_parse_restart_interval(&stream,
> +                                                       &out-
> >restart_interval);
> +                       break;
> +
> +               case SOS:
> +                       ret = jpeg_reference_segment(&stream, &out-
> >sos);
> +                       if (ret < 0)
> +                               return ret;
> +                       ret = jpeg_parse_scan_header(&stream, out-
> >scan);
> +                       /*
> +                        * stop parsing, the scan header marks the
> beginning of
> +                        * the entropy coded segment
> +                        */
> +                       out->ecs_offset = stream.curr - (u8 *)buf;
> +                       return ret;
> +
> +               /* markers without parameters */
> +               case RST0 ... RST7: /* restart */
> +               case SOI: /* start of image */
> +               case EOI: /* end of image */
> +                       break;
> +
> +               /* skip unknown or unsupported marker segments */
> +               default:
> +                       ret = jpeg_skip_segment(&stream);
> +                       break;
> +               }
> +               if (ret < 0)
> +                       return ret;
> +       }
> +
> +       return marker;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_jpeg_parse_header);
> +
> +/**
> + * v4l2_jpeg_parse_frame_header - parse frame header
> + * @buf: address of the frame header, after the SOF0 marker
> + * @len: length of the frame header
> + * @frame_header: returns the parsed frame header
> + *
> + * Returns 0 or negative error if parsing failed.
> + */
> +int v4l2_jpeg_parse_frame_header(void *buf, size_t len,
> +                                struct v4l2_jpeg_frame_header
> *frame_header)
> +{
> +       struct jpeg_stream stream;
> +
> +       stream.curr = buf;
> +       stream.end = stream.curr + len;
> +       return jpeg_parse_frame_header(&stream, frame_header);
> +}
> +EXPORT_SYMBOL_GPL(v4l2_jpeg_parse_frame_header);
> +
> +/**
> + * v4l2_jpeg_parse_scan_header - parse scan header
> + * @buf: address of the scan header, after the SOS marker
> + * @len: length of the scan header
> + * @scan_header: returns the parsed scan header
> + *
> + * Returns 0 or negative error if parsing failed.
> + */
> +int v4l2_jpeg_parse_scan_header(void *buf, size_t len,
> +                               struct v4l2_jpeg_scan_header
> *scan_header)
> +{
> +       struct jpeg_stream stream;
> +
> +       stream.curr = buf;
> +       stream.end = stream.curr + len;
> +       return jpeg_parse_scan_header(&stream, scan_header);
> +}
> +EXPORT_SYMBOL_GPL(v4l2_jpeg_parse_scan_header);
> +
> +/**
> + * v4l2_jpeg_parse_quantization_tables - parse quantization tables
> segment
> + * @buf: address of the quantization table segment, after the DQT
> marker
> + * @len: length of the quantization table segment
> + * @q_tables: returns four references into the buffer for the
> + *            four possible quantization table destinations
> + *
> + * Returns 0 or negative error if parsing failed.
> + */
> +int v4l2_jpeg_parse_quantization_tables(void *buf, size_t len,
> +                                       struct v4l2_jpeg_reference
> *q_tables)
> +{
> +       struct jpeg_stream stream;
> +
> +       stream.curr = buf;
> +       stream.end = stream.curr + len;
> +       return jpeg_parse_quantization_tables(&stream, q_tables);
> +}
> +EXPORT_SYMBOL_GPL(v4l2_jpeg_parse_quantization_tables);
> +
> +/**
> + * v4l2_jpeg_parse_huffman_tables - parse huffman tables segment
> + * @buf: address of the Huffman table segment, after the DHT marker
> + * @len: length of the Huffman table segment
> + * @huffman_tables: returns four references into the buffer for the
> + *                  four possible Huffman table destinations, in
> + *                  the order DC0, DC1, AC0, AC1
> + *
> + * Returns 0 or negative error if parsing failed.
> + */
> +int v4l2_jpeg_parse_huffman_tables(void *buf, size_t len,
> +                                  struct v4l2_jpeg_reference
> *huffman_tables)
> +{
> +       struct jpeg_stream stream;
> +
> +       stream.curr = buf;
> +       stream.end = stream.curr + len;
> +       return jpeg_parse_huffman_tables(&stream, huffman_tables);
> +}
> +EXPORT_SYMBOL_GPL(v4l2_jpeg_parse_huffman_tables);
> diff --git a/include/media/v4l2-jpeg.h b/include/media/v4l2-jpeg.h
> new file mode 100644
> index 000000000000..2f6292c75122
> --- /dev/null
> +++ b/include/media/v4l2-jpeg.h
> @@ -0,0 +1,135 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * V4L2 JPEG helpers header
> + *
> + * Copyright (C) 2019 Pengutronix, Philipp Zabel <kernel@pengutronix
> .de>
> + *
> + * For reference, see JPEG ITU-T.81 (ISO/IEC 10918-1)
> + */
> +
> +#ifndef _V4L2_JPEG_H
> +#define _V4L2_JPEG_H
> +
> +#include <linux/v4l2-controls.h>
> +
> +#define V4L2_JPEG_MAX_COMPONENTS       3

And V4L2_JPEG_MAX_COMPONENTS 4 is neccesary (imx8, ARGB), not sure it
other changes needed...

> +#define V4L2_JPEG_MAX_TABLES           4
> +
> +/**
> + * struct v4l2_jpeg_reference - reference into the JPEG buffer
> + * @start: pointer to the start of the referenced segment or table
> + * @length: size of the referenced segment or table
> + *
> + * Wnen referencing marker segments, start points right after the
> marker code,
> + * and length is the size of the segment parameters, excluding the
> marker code.
> + */
> +struct v4l2_jpeg_reference {
> +       u8 *start;
> +       size_t length;
> +};
> +
> +/* B.2.2 Frame header syntax */
> +
> +/**
> + * struct v4l2_jpeg_frame_component_spec - frame component-
> specification
> + * @component_identifier: C[i]
> + * @horizontal_sampling_factor: H[i]
> + * @vertical_sampling_factor: V[i]
> + * @quantization_table_selector: quantization table destination
> selector Tq[i]
> + */
> +struct v4l2_jpeg_frame_component_spec {
> +       u8 component_identifier;
> +       u8 horizontal_sampling_factor;
> +       u8 vertical_sampling_factor;
> +       u8 quantization_table_selector;
> +};
> +
> +/**
> + * struct v4l2_jpeg_frame_header - JPEG frame header
> + * @height: Y
> + * @width: X
> + * @precision: P
> + * @num_components: Nf
> + * @component: component-specification, see
> v4l2_jpeg_frame_component_spec
> + * @subsampling: decoded subsampling from component-specification
> + */
> +struct v4l2_jpeg_frame_header {
> +       u16 height;
> +       u16 width;
> +       u8 precision;
> +       u8 num_components;
> +       struct v4l2_jpeg_frame_component_spec
> component[V4L2_JPEG_MAX_COMPONENTS];
> +       enum v4l2_jpeg_chroma_subsampling subsampling;
> +};
> +
> +/* B.2.3 Scan header syntax */
> +
> +/**
> + * struct v4l2_jpeg_scan_component_spec - scan component-
> specification
> + * @component_selector: Cs[j]
> + * @dc_entropy_coding_table_selector: Td[j]
> + * @ac_entropy_coding_table_selector: Ta[j]
> + */
> +struct v4l2_jpeg_scan_component_spec {
> +       u8 component_selector;
> +       u8 dc_entropy_coding_table_selector;
> +       u8 ac_entropy_coding_table_selector;
> +};
> +
> +/**
> + * struct v4l2_jpeg_scan_header - JPEG scan header
> + * @num_components: Ns
> + * @component: component-specification, see
> v4l2_jpeg_scan_component_spec
> + */
> +struct v4l2_jpeg_scan_header {
> +       u8 num_components;                              /* Ns */
> +       struct v4l2_jpeg_scan_component_spec
> component[V4L2_JPEG_MAX_COMPONENTS];
> +       /* Ss, Se, Ah, and Al are not used by any driver */
> +};
> +
> +/**
> + * struct v4l2_jpeg_header - parsed JPEG header
> + * @sof: pointer to frame header and size
> + * @sos: pointer to scan header and size
> + * @dht: pointers to huffman tables and sizes
> + * @dqt: pointers to quantization tables and sizes
> + * @frame: parsed frame header
> + * @scan: pointer to parsed scan header, optional
> + * @quantization_tables: references to four quantization tables,
> optional
> + * @huffman_tables: references to four Huffman tables in DC0, DC1,
> AC0, AC1
> + *                  order, optional
> + * @restart_interval: number of MCU per restart interval, Ri
> + * @ecs_offset: buffer offset in bytes to the entropy coded segment
> + *
> + * When this structure is passed to v4l2_jpeg_parse_header, the
> optional scan,
> + * quantization_tables, and huffman_tables pointers must be
> initialized to NULL
> + * or point at valid memory.
> + */
> +struct v4l2_jpeg_header {
> +       struct v4l2_jpeg_reference sof;
> +       struct v4l2_jpeg_reference sos;
> +       unsigned int num_dht;
> +       struct v4l2_jpeg_reference dht[V4L2_JPEG_MAX_TABLES];
> +       unsigned int num_dqt;
> +       struct v4l2_jpeg_reference dqt[V4L2_JPEG_MAX_TABLES];
> +
> +       struct v4l2_jpeg_frame_header frame;
> +       struct v4l2_jpeg_scan_header *scan;
> +       struct v4l2_jpeg_reference *quantization_tables;
> +       struct v4l2_jpeg_reference *huffman_tables;
> +       u16 restart_interval;
> +       size_t ecs_offset;
> +};
> +
> +int v4l2_jpeg_parse_header(void *buf, size_t len, struct
> v4l2_jpeg_header *out);
> +
> +int v4l2_jpeg_parse_frame_header(void *buf, size_t len,
> +                                struct v4l2_jpeg_frame_header
> *frame_header);
> +int v4l2_jpeg_parse_scan_header(void *buf, size_t len,
> +                               struct v4l2_jpeg_scan_header
> *scan_header);
> +int v4l2_jpeg_parse_quantization_tables(void *buf, size_t len,
> +                                       struct v4l2_jpeg_reference
> *q_tables);
> +int v4l2_jpeg_parse_huffman_tables(void *buf, size_t len,
> +                                  struct v4l2_jpeg_reference
> *huffman_tables);
> +
> +#endif
> --
> 2.20.1
>