Message-ID: <CAAEAJfB1JCrVTVBMs_kFnuM1NrUi=j5+N9WAi6N5PUH5L6tHfw@mail.gmail.com>
Date:   Thu, 21 Jul 2022 13:18:19 -0300
From:   Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
To:     Sebastian Fricke <sebastian.fricke@...labora.com>
Cc:     Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Robin Murphy <robin.murphy@....com>,
        linux-media <linux-media@...r.kernel.org>,
        Jernej Škrabec <jernej.skrabec@...il.com>,
        Alex Bee <knaerzche@...il.com>,
        Collabora Kernel ML <kernel@...labora.com>,
        Robert Beckett <bob.beckett@...labora.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        "open list:STAGING SUBSYSTEM" <linux-staging@...ts.linux.dev>,
        Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH 0/6] RkVDEC HEVC driver

On Thu, Jul 21, 2022 at 1:16 PM Sebastian Fricke
<sebastian.fricke@...labora.com> wrote:
>
> Hey Nicolas & Robin,
>
> Thanks for the feedback.
>
> On 15.07.2022 11:36, Nicolas Dufresne wrote:
> >Le vendredi 15 juillet 2022 à 12:04 +0100, Robin Murphy a écrit :
> >> On 2022-07-13 17:24, Sebastian Fricke wrote:
> >> > Implement the HEVC codec variation for the RkVDEC driver. Currently only
> >> > the RK3399 is supported, but it is possible to enable the RK3288 as it
> >> > also supports this codec.
> >> >
> >> > Based on top of the media tree @ef7fcbbb9eabbe86d2287484bf366dd1821cc6b8
> >> > and the HEVC uABI MR by Benjamin Gaignard.
> >> > (https://patchwork.linuxtv.org/project/linux-media/list/?series=8360)
> >> >
> >> > Tested with the GStreamer V4L2 HEVC plugin:
> >> > (https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1079)
> >> >
> >> > Current Fluster score:
> >> > `Ran 131/147 tests successfully               in 278.568 secs`
> >> > with
> >> > `python3 fluster.py run -d GStreamer-H.265-V4L2SL-Gst1.0 -ts JCT-VC-HEVC_V1 -j1`
> >> >
> >> > failed conformance tests:
> >> > - DBLK_D_VIXS_2 (Success on Hantro G2)
> >> > - DSLICE_A_HHI_5 (Success on Hantro G2)
> >> > - EXT_A_ericsson_4 (Success on Hantro G2)
> >> > - PICSIZE_A_Bossen_1 (Hardware limitation)
> >> > - PICSIZE_B_Bossen_1 (Hardware limitation)
> >> > - PICSIZE_C_Bossen_1 (Hardware limitation)
> >> > - PICSIZE_D_Bossen_1 (Hardware limitation)
> >> > - PPS_A_qualcomm_7 (Success on Hantro G2)
> >> > - SAODBLK_A_MainConcept_4 (Success on Hantro G2)
> >> > - SAODBLK_B_MainConcept_4 (Success on Hantro G2)
> >> > - SLIST_B_Sony_9 (Success on Hantro G2)
> >> > - SLIST_D_Sony_9 (Success on Hantro G2)
> >> > - TSUNEQBD_A_MAIN10_Technicolor_2 (Success on Hantro G2)
> >> > - VPSSPSPPS_A_MainConcept_1 (Success on Hantro G2)
> >> > - WPP_D_ericsson_MAIN10_2 (Fail on Hantro G2)
> >> > - WPP_D_ericsson_MAIN_2 (Fail on Hantro G2)
> >> >
> >> > Not tested with FFMpeg so far.
> >> >
> >> > Known issues:
> >> > - Unable to reliably decode multiple videos concurrently
> >> > - The SAODBLK_* tests timeout if the timeout time in fluster is lower than 120
> >> > - Currently the uv_virstride is calculated in a manner that is hardcoded
> >> > for the two available formats NV12 and NV15. (@config_registers)
> >> >
> >> > Notable design decisions:
> >> > - I opted for a bitfield to represent the PPS memory blob as it is the
> >> > perfect tool for that job. It describes the memory layout with any
> >> > additional required documentation, is easy to read and a native language
> >> > tool for that job
> >>
> >> Can I point out how terrible an idea this is? The C language gives
> >> virtually zero guarantee about how bitfields are actually represented in
> >> memory. Platform ABIs (e.g. [1]) might nail things down a bit more, but
> >> different platforms are free to make completely different choices so
> >> portability still goes out the window. Even for a single platform,
> >> different compilers (or at worst even different version of one compiler)
> >> can still make incompatible choices e.g. WRT alignment of packed
> >> members. Even if you narrow the scope as far as a specific version of
> >> AArch64 GCC, I think this is still totally broken for big-endian.
> >>
> >> The fact that you've had to use nonsensical types to trick a compiler
> >> into meeting your expectations should already be a clue to how fragile
> >> this is in general.
> >>
> >> > - The RPS memory blob is created using a bitmap implementation, which
> >> > uses a common Kernel API to avoid reinventing the wheel and to keep the
> >> > code clean.
> >>
> >> Similarly, Linux bitmaps are designed for use as, well, bitmaps. Abusing
> >> them as a data interchange format for bit-aligned numerical values is
> >> far from "clean" semantically. And I'm pretty sure it's also broken for
> >> big-endian.
> >>
> >> This kind of stuff may be standard practice in embedded development
> >> where you're targeting a specific MCU with a specific toolchain, but I
> >> don't believe it's suitable for upstream Linux. It would take pretty
> >> much the same number of lines to use GENMASK definitions and bitfield.h
> >> helpers to pack values into words which can then be written to memory in
> >> a guaranteed format and endianness (certainly for the PPS; for the RPS
> >> it may well end up a bit longer, but would be self-documenting and
> >> certainly more readable than those loops). It mostly just means that for
> >> any field which crosses a word boundary you'll end up with 2 definitions
> >> and 2 assignments, which is hardly a problem (and in some ways more
> >> honest about what's actually going on).
> >
> >Thanks for the feedback, in multimedia (unlike register programming), we don't
> >really consider bitstreams as bitmap or bitfield. What we do really expect is to
> >use bit writer helpers (and sometimes a bit reader though we try and avoid the
> >second one in the  kernel). Its more of less a cursor (a bit position) into a
> >memory that advance while writing. A bit writer should help protect against
> >overflow too.
> >
> >When writing lets say a chain of 8 bits from a char, a proper helper is expected
> >to be very explicit on the ordering (write_u8_le/be or something better worded).
> >I would rather like to see all these blobs written this way personally then
> >having a cleared buffer and writing using bit offsets.
> >
> >Perhaps I may suggest to start with implementing just that inside this driver?
> >It isn't very hard, and then the implementation can be reduced later and shared
> >later, with whatever exists without deviating from the intent of the existing
> >API ? I do believe that having this in linux-media can be useful in the future.
> >We will notably need to extend such a helper with multimedia specific coding
> >technique (golomb, boolean coding, etc.) for use in stateless encoder drivers.
>
> I currently design a general bit-writer API to handle the mentioned
> issues correctly. I'll post it as part of V2, due to my current workload
> this will happen in 3 weeks at the earliest.
>

I wonder if this is really the correct approach.

Introducing a new API and adding HEVC support at the same time,
sounds like scope creep to me.

How about you first introduce HEVC and then we move to the new API?
A generic bit-writer API might really take a long time to get mainlined.

Thanks!
Ezequiel

> >
> >Nicolas
> >
> >>
> >> Thanks,
> >> Robin.
>
> Greetings,
> Sebastian
>
> >>
> >> [1]
> >> https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst#bit-fields
> >>
> >> > - I deliberatly opted against the macro solution used in H264, which
> >> > declares Macros in mid function and declares the fields of the memory
> >> > blob as macros as well. And I would be glad to refactor the H264 code if
> >> > desired by the maintainer to use common Kernel APIs and native language
> >> > elements.
> >> > - The giant static array of cabac values is moved to a separate c file,
> >> > I did so because a separate .h file would be incorrect as it doesn't
> >> > expose anything of any value for any other file than the rkvdec-hevc.c
> >> > file. Other options were:
> >> >    - Calculating the values instead of storing the results (doesn't seem
> >> >    to be worth it)
> >> >    - Supply them via firmware (Adding firmware makes the whole software
> >> >    way more complicated and the usage of the driver less obvious)
> >> >
> >> > Ignored Checkpatch warnings (as it fits to the current style of the file):
> >> > ```
> >> > WARNING: line length of 162 exceeds 100 columns
> >> > #115: FILE: drivers/media/v4l2-core/v4l2-common.c:265:
> >> > +               { .format = V4L2_PIX_FMT_NV15,    .pixel_enc = V4L2_PIXEL_ENC_YUV, .mem_planes = 1, .comp_planes = 2, .bpp = { 5, 5, 0, 0 }, .hdiv = 2, .vdiv = 2,
> >> >
> >> > ERROR: trailing statements should be on next line
> >> > #128: FILE: drivers/media/v4l2-core/v4l2-ioctl.c:1305:
> >> > +       case V4L2_PIX_FMT_NV15:         descr = "10-bit Y/CbCr 4:2:0 (Packed)"; break;
> >> > ```
> >> >
> >> > v4l2-compliance test:
> >> > ```
> >> > Total for rkvdec device /dev/video3: 46, Succeeded: 46, Failed: 0, Warnings: 0
> >> > ```
> >> >
> >> > kselftest module run for the bitmap changes:
> >> > ```
> >> > $ sudo insmod /usr/lib/modules/5.19.0-rc3-finalseries/kernel/lib/test_bitmap.ko
> >> > [   71.751716] test_bitmap: parselist: 14: input is '0-2047:128/256' OK, Time: 1750
> >> > [   71.751787] test_bitmap: bitmap_print_to_pagebuf: input is '0-32767
> >> > [   71.751787] ', Time: 6708
> >> > [   71.760373] test_bitmap: set_value: 6/6 tests correct
> >> > ```
> >> >
> >> > Jonas Karlman (2):
> >> >    media: v4l2: Add NV15 pixel format
> >> >    media: v4l2-common: Add helpers to calculate bytesperline and
> >> >      sizeimage
> >> >
> >> > Sebastian Fricke (4):
> >> >    bitops: bitmap helper to set variable length values
> >> >    staging: media: rkvdec: Add valid pixel format check
> >> >    staging: media: rkvdec: Enable S_CTRL IOCTL
> >> >    staging: media: rkvdec: Add HEVC backend
> >> >
> >> >   .../media/v4l/pixfmt-yuv-planar.rst           |   53 +
> >> >   drivers/media/v4l2-core/v4l2-common.c         |   79 +-
> >> >   drivers/media/v4l2-core/v4l2-ioctl.c          |    1 +
> >> >   drivers/staging/media/rkvdec/Makefile         |    2 +-
> >> >   drivers/staging/media/rkvdec/TODO             |   22 +-
> >> >   .../staging/media/rkvdec/rkvdec-hevc-data.c   | 1844 +++++++++++++++++
> >> >   drivers/staging/media/rkvdec/rkvdec-hevc.c    |  859 ++++++++
> >> >   drivers/staging/media/rkvdec/rkvdec-regs.h    |    1 +
> >> >   drivers/staging/media/rkvdec/rkvdec.c         |  182 +-
> >> >   drivers/staging/media/rkvdec/rkvdec.h         |    3 +
> >> >   include/linux/bitmap.h                        |   39 +
> >> >   include/uapi/linux/videodev2.h                |    1 +
> >> >   lib/test_bitmap.c                             |   47 +
> >> >   13 files changed, 3066 insertions(+), 67 deletions(-)
> >> >   create mode 100644 drivers/staging/media/rkvdec/rkvdec-hevc-data.c
> >> >   create mode 100644 drivers/staging/media/rkvdec/rkvdec-hevc.c
> >> >
> >>
> >

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