Re: [PATCH 00/18] Add Hantro regmap and VC8000 h264 decode support

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Hi Jonas,

On Mon, 12 Oct 2020, Jonas Karlman <jonas@xxxxxxxxx> wrote:
Hi, On 2020-10-12 22:59, Adrian Ratiu wrote:
Dear all, This series introduces a regmap infrastructure for the Hantro driver which is used to compensate for different HW-revision register layouts. To justify it h264 decoding capability is added for newer VC8000 chips. This is a gradual conversion to the new infra - a complete conversion would have been very big and I do not have all the HW yet to test (I'm expecting a RK3399 shipment next week though ;). I think converting the h264 decoder provides a nice blueprint for how the other codecs can be converted and enabled for different HW revisions. The end goal of this is to make the driver more generic and eliminate entirely custom boilerplate like `struct hantro_reg` or headers with core-specific bit manipulations like `hantro_g1_regs.h` and instead rely on the well-tested albeit more verbose regmap subsytem. To give just two examples of bugs which are easily discovered by using more verbose regmap fields (very easy to compare with the datasheets) instead of relying on bit-magic tricks: G1_REG_DEC_CTRL3_INIT_QP(x) was off-by-1 and the wrong .clk_gate bit was set in hantro_postproc.c. Anyway, this series also extends the MMIO regmap API to allow relaxed writes for the theoretical reason that avoiding unnecessary membarriers leads to less CPU usage and small improvements to battery life. However, in practice I could not measure differences between relaxed/non-relaxed IO, so I'm on the fence whether to keep or remove the relaxed calls. What I could masure is the performance impact of adding more sub-reg field acesses: a constant ~ 20 microsecond bump per G1 h264 frame. This is acceptable considering the total time to decode a frame takes three orders of magnitude longer, i.e. miliseconds ranges, depending on the frame size and bitstream params, so it is an acceptable trade-off to have a more generic driver.

In the RK3399 variant all fields use completely different positions so in order to make the driver fully generic all around 145 sub-reg fields used for h264 needs to be converted, see [1] for a quick generation of field mappings used for h264 decoding. Any indication on how the performance will be impacted with 145 fields compared to around 20 fields used in this series?

I'm aware of the RK3399 bigger layout divergence and have some commits converting more of the reg fields, but not all that is required for h264 on rk3399. I haven't seen a huge perf degradation but more measurements are needed, basically it depends on how often we go from writing a reg once to multiple times due to splitting.

I tried some benchmarks using regmap caching (both the default backends provided by the regmap subsystem, and a custom one I wrote) but they were not helping, perhaps if we had more fields then that would have more of an impact.

(btw some good news is I'm having a RK3399 SoC in the mail for an unrelated project and expect to receive it soon :D)

IMO there will always be a trade-off between optimizing the driver to squeeze the most perf out of the HW, eg optimize reg writes at low microsec level (which I think here is unnecessary) and making it more generic to support more HW.

In this case a fundamental question we need to ask ourselves is if the RK3399 "looks like another/different-enough HW" due to its bigger reg shuffling to warrant a separate driver or driver-within-a-driver architecture instead trying to bring it into the fold with the others, possibly degrading perf for everyone. I guess we'll have to see some benchmark numbers and an actual h264 implementation before deciding how to proceed with RK3399.


Another issue with RK3399 variant is that some fields use different position depending on the codec used, e.g. two dec_ref_frames in [2]. Should we use codec specific field maps? or any other suggestion on how we can handle such case?

Yes, codec specific fields would be one idea, but I'd try to avoid it if possible to avoid unnecessary field definitions.

The regmap field API and config we currently use are just a flat structs (see hantro_regmap.[h|c]) but it doesn't have to be like that. Maybe we could organize it a bit better and in the future have some codec-level configs going on due to the regmap subsystem allowing de-coupling of the API (struct regmap_field) from the reg defs/configs (struct reg_field).

That is just an idea of the top of my head :) Will have to think a bit more about how to handle that specific use case in the future. Thanks!


[1] https://github.com/Kwiboo/rockchip-vpu-regtool/commit/8b88d94d2ed966c7d88d9a735c0c97368eb6c92d
[2] https://github.com/Kwiboo/rockchip-vpu-regtool/blob/master/rk3399_dec_regs.c#L1065
[3] https://github.com/Kwiboo/rockchip-vpu-regtool/commit/9498326296445a9ce153b585cc48e0cea05d3c93

Best regards,
Jonas


This has been tested on next-20201009 with imx8mq for G1 and an SoC with
VC8000 which has not yet been added (hopefuly support lands soon).

Kind regards,
Adrian

Adrian Ratiu (18):
  media: hantro: document all int reg bits up to vc8000
  media: hantro: make consistent use of decimal register notation
  media: hantro: make G1_REG_SOFT_RESET Rockchip specific
  media: hantro: add reset controller support
  media: hantro: prepare clocks before variant inits are run
  media: hantro: imx8mq: simplify ctrlblk reset logic
  regmap: mmio: add config option to allow relaxed MMIO accesses
  media: hantro: add initial MMIO regmap infrastructure
  media: hantro: default regmap to relaxed MMIO
  media: hantro: convert G1 h264 decoder to regmap fields
  media: hantro: convert G1 postproc to regmap
  media: hantro: add VC8000D h264 decoding
  media: hantro: add VC8000D postproc support
  media: hantro: make PP enablement logic a bit smarter
  media: hantro: add user-selectable, platform-selectable H264 High10
  media: hantro: rename h264_dec as it's not G1 specific anymore
  media: hantro: add dump registers debug option before decode start
  media: hantro: document encoder reg fields

 drivers/base/regmap/regmap-mmio.c             |   34 +-
 drivers/staging/media/hantro/Makefile         |    3 +-
 drivers/staging/media/hantro/hantro.h         |   79 +-
 drivers/staging/media/hantro/hantro_drv.c     |   41 +-
 drivers/staging/media/hantro/hantro_g1_regs.h |   92 +-
 ...hantro_g1_h264_dec.c => hantro_h264_dec.c} |  237 +++-
 drivers/staging/media/hantro/hantro_hw.h      |   23 +-
 .../staging/media/hantro/hantro_postproc.c    |  144 ++-
 drivers/staging/media/hantro/hantro_regmap.c  | 1015 +++++++++++++++++
 drivers/staging/media/hantro/hantro_regmap.h  |  295 +++++
 drivers/staging/media/hantro/hantro_v4l2.c    |    3 +-
 drivers/staging/media/hantro/imx8m_vpu_hw.c   |   75 +-
 drivers/staging/media/hantro/rk3288_vpu_hw.c  |    5 +-
 include/linux/regmap.h                        |    5 +
 14 files changed, 1795 insertions(+), 256 deletions(-)
 rename drivers/staging/media/hantro/{hantro_g1_h264_dec.c => hantro_h264_dec.c} (58%)
 create mode 100644 drivers/staging/media/hantro/hantro_regmap.c
 create mode 100644 drivers/staging/media/hantro/hantro_regmap.h




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