From: Ezequiel Garcia <email@example.com>
To: Chen-Yu Tsai <firstname.lastname@example.org>
Cc: Hans Verkuil <email@example.com>,
Philipp Zabel <firstname.lastname@example.org>,
Mauro Carvalho Chehab <email@example.com>,
Greg Kroah-Hartman <firstname.lastname@example.org>,
"open list:ARM/Rockchip SoC..."
"open list:STAGING SUBSYSTEM" <email@example.com>,
Linux Kernel Mailing List <firstname.lastname@example.org>
Subject: Re: [PATCH RFT v2 1/8] media: hantro: jpeg: Relax register writes before write starting hardware
Date: Wed, 19 Jan 2022 08:59:51 -0300 [thread overview]
Message-ID: <CAAEAJfBM4d4hd1Av_TO-WVXQoUCNUckm+YHawdg6PY3urkB9nA@mail.gmail.com> (raw)
On Wed, 19 Jan 2022 at 07:09, Chen-Yu Tsai <email@example.com> wrote:
> On Wed, Jan 19, 2022 at 5:02 AM Ezequiel Garcia
> <firstname.lastname@example.org> wrote:
> > Hi Chen-Yu,
> > The series looks good, thanks for picking up this task.
> > Just a one comment.
> > On Fri, Jan 07, 2022 at 05:34:48PM +0800, Chen-Yu Tsai wrote:
> > > In the earlier submissions of the Hantro/Rockchip JPEG encoder driver, a
> > > wmb() was inserted before the final register write that starts the
> > > encoder. In v11, it was removed and the second-to-last register write
> > > was changed to a non-relaxed write, which has an implicit wmb() .
> > > The rockchip_vpu2 (then rk3399_vpu) variant is even weirder as there
> > > is another writel_relaxed() following the non-relaxed one.
> > >
> > > Turns out only the last writel() needs to be non-relaxed. Device I/O
> > > mappings already guarantee strict ordering to the same endpoint, and
> > > the writel() triggering the hardware would force all writes to memory
> > > to be observed before the writel() to the hardware is observed.
> > >
> > >  https://lore.kernel.org/linux-media/CAAFQd5ArFG0hU6MgcyLd+_UOP3+T_U-aw2FXv6sE7fGqVCVGqw@mail.gmail.com/
> > >
> > > Signed-off-by: Chen-Yu Tsai <email@example.com>
> > > ---
> > > drivers/staging/media/hantro/hantro_h1_jpeg_enc.c | 3 +--
> > > drivers/staging/media/hantro/rockchip_vpu2_hw_jpeg_enc.c | 3 +--
> > > 2 files changed, 2 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/staging/media/hantro/hantro_h1_jpeg_enc.c b/drivers/staging/media/hantro/hantro_h1_jpeg_enc.c
> > > index 1450013d3685..03db1c3444f8 100644
> > > --- a/drivers/staging/media/hantro/hantro_h1_jpeg_enc.c
> > > +++ b/drivers/staging/media/hantro/hantro_h1_jpeg_enc.c
> > > @@ -123,8 +123,7 @@ int hantro_h1_jpeg_enc_run(struct hantro_ctx *ctx)
> > > | H1_REG_AXI_CTRL_INPUT_SWAP32
> > > | H1_REG_AXI_CTRL_OUTPUT_SWAP8
> > > | H1_REG_AXI_CTRL_INPUT_SWAP8;
> > > - /* Make sure that all registers are written at this point. */
> > > - vepu_write(vpu, reg, H1_REG_AXI_CTRL);
> > > + vepu_write_relaxed(vpu, reg, H1_REG_AXI_CTRL);
> > >
> > As far as I can remember, this logic comes from really old Chromium Kernels.
> > You might be right, and this barrier isn't needed... but then OTOH the comment
> > is here for a reason, so maybe it is needed (or was needed on some RK3288 SoC revision).
> I just realized that my commit log is wrong.
> " ... a wmb() was inserted before the final register write that starts the
> encoder. ... " . It is actually before the second-to-last register write.
> > I don't have RK3288 boards near me, but in any case, I'm not sure
> > we'd be able to test this easily (maybe there are issues that only
> > trigger under a certain load).
> I see. I do have a Veyron around that I haven't used in awhile. But as you
> said, it might not be an obvious hardware limitation.
> > I'd personally avoid this one change, but if you are confident enough with it
> > that's fine too.
> Unfortunately they didn't leave a whole lot of clues around. For most hardware,
> as I mentioned in the commit log, I think the final non-relaxed write should
> suffice. I'd point to the decoder drivers not having any barriers or
> non-relaxed writes except the final one, but IIUC they are actually two
> distinct pieces of hardware.
> I suspect we will never know. This JPEG encoder doesn't seem to get used
> a lot. The VP8 and H.264 encoders on ChromeOS work correctly without the
> extra barrier and get tested a lot, but that's only testing the RK3399.
> Hans, would it be possible for you to skip this patch and pick the rest?
> Or would you like me to resent without this one?
If you decide to resend, feel free to add:
Reviewed-by: Ezequiel Garcia <firstname.lastname@example.org>
to the whole series.
Linux-rockchip mailing list
next prev parent reply other threads:[~2022-01-19 12:00 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-07 9:34 [PATCH RFT v2 0/8] media: hantro: jpeg: Various improvements Chen-Yu Tsai
2022-01-07 9:34 ` [PATCH RFT v2 1/8] media: hantro: jpeg: Relax register writes before write starting hardware Chen-Yu Tsai
2022-01-18 21:02 ` Ezequiel Garcia
2022-01-19 10:08 ` Chen-Yu Tsai
2022-01-19 11:59 ` Ezequiel Garcia [this message]
2022-01-20 14:20 ` Hans Verkuil
2022-01-21 2:25 ` Chen-Yu Tsai
2022-01-07 9:34 ` [PATCH RFT v2 2/8] media: hantro: Fix overfill bottom register field name Chen-Yu Tsai
2022-01-07 9:34 ` [PATCH RFT v2 3/8] media: hantro: Support cropping visible area for encoders Chen-Yu Tsai
2022-01-07 9:34 ` [PATCH RFT v2 4/8] media: hantro: jpeg: Add JFIF APP0 segment to JPEG encoder output Chen-Yu Tsai
2022-01-07 9:34 ` [PATCH RFT v2 5/8] media: hantro: jpeg: Add COM segment to JPEG header to align image scan Chen-Yu Tsai
2022-01-07 9:34 ` [PATCH RFT v2 6/8] media: hantro: Implement V4L2_CID_JPEG_ACTIVE_MARKER control Chen-Yu Tsai
2022-01-07 9:34 ` [PATCH RFT v2 7/8] media: hantro: output encoded JPEG content directly to capture buffers Chen-Yu Tsai
2022-01-07 9:34 ` [PATCH RFT v2 8/8] media: hantro: jpeg: Remove open-coded size in quantization table code Chen-Yu Tsai
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