Re: [PATCH] media: staging: imgu: make imgu work on low frequency for low input

[Tomasz Figa <tfiga@chromium.org>]

On Fri, Aug 16, 2019 at 3:52 PM Bingbu Cao <bingbu.cao@linux.intel.com> wrote:
>
> Hi, Tomasz
>
> Thanks for your review.
>
> On 8/16/19 2:10 PM, Tomasz Figa wrote:
> > Hi Bingbu,
> >
> > On Fri, Aug 16, 2019 at 12:25 PM <bingbu.cao@intel.com> wrote:
> >>
> >> From: Bingbu Cao <bingbu.cao@intel.com>
> >>
> >> Currently, imgu is working on 450MHz for all cases, however
> >> in some cases (input frame less than 2.3MP), the imgu
> >> did not need work in high frequency.
> >> This patch make imgu work on 200MHz if the imgu input
> >> frame is less than 2.3MP to save power.
> >>
> >
> > Thanks for the patch! Please see my comments inline.
> >
> >> Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
> >> ---
> >>  drivers/staging/media/ipu3/ipu3-css.c  | 7 ++++---
> >>  drivers/staging/media/ipu3/ipu3-css.h  | 3 ++-
> >>  drivers/staging/media/ipu3/ipu3-v4l2.c | 6 ++++++
> >>  drivers/staging/media/ipu3/ipu3.c      | 6 ++++--
> >>  drivers/staging/media/ipu3/ipu3.h      | 1 +
> >>  5 files changed, 17 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/staging/media/ipu3/ipu3-css.c b/drivers/staging/media/ipu3/ipu3-css.c
> >> index fd1ed84c400c..590ed7e182a6 100644
> >> --- a/drivers/staging/media/ipu3/ipu3-css.c
> >> +++ b/drivers/staging/media/ipu3/ipu3-css.c
> >> @@ -210,12 +210,13 @@ static int imgu_hw_wait(void __iomem *base, int reg, u32 mask, u32 cmp)
> >>
> >>  /* Initialize the IPU3 CSS hardware and associated h/w blocks */
> >>
> >> -int imgu_css_set_powerup(struct device *dev, void __iomem *base)
> >> +int imgu_css_set_powerup(struct device *dev, void __iomem *base, bool low_power)
> >>  {
> >> -       static const unsigned int freq = 450;
> >> +       unsigned int freq;
> >
> > How about making freq the argument to this function rather than
> > introducing some artificial boolean?
> Let me try to move the check into imgu_powerup().
> >
> >>         u32 pm_ctrl, state, val;
> >>
> >> -       dev_dbg(dev, "%s\n", __func__);
> >> +       freq = low_power ? 200 : 450;
> >> +       dev_dbg(dev, "%s with freq %u\n", __func__, freq);
> >>         /* Clear the CSS busy signal */
> >>         readl(base + IMGU_REG_GP_BUSY);
> >>         writel(0, base + IMGU_REG_GP_BUSY);
> >> diff --git a/drivers/staging/media/ipu3/ipu3-css.h b/drivers/staging/media/ipu3/ipu3-css.h
> >> index 6b8bab27ab1f..882936a9dae9 100644
> >> --- a/drivers/staging/media/ipu3/ipu3-css.h
> >> +++ b/drivers/staging/media/ipu3/ipu3-css.h
> >> @@ -187,7 +187,8 @@ bool imgu_css_is_streaming(struct imgu_css *css);
> >>  bool imgu_css_pipe_queue_empty(struct imgu_css *css, unsigned int pipe);
> >>
> >>  /******************* css hw *******************/
> >> -int imgu_css_set_powerup(struct device *dev, void __iomem *base);
> >> +int imgu_css_set_powerup(struct device *dev, void __iomem *base,
> >> +                        bool low_power);
> >>  void imgu_css_set_powerdown(struct device *dev, void __iomem *base);
> >>  int imgu_css_irq_ack(struct imgu_css *css);
> >>
> >> diff --git a/drivers/staging/media/ipu3/ipu3-v4l2.c b/drivers/staging/media/ipu3/ipu3-v4l2.c
> >> index 3c7ad1eed434..dcc2a0476e49 100644
> >> --- a/drivers/staging/media/ipu3/ipu3-v4l2.c
> >> +++ b/drivers/staging/media/ipu3/ipu3-v4l2.c
> >> @@ -182,6 +182,12 @@ static int imgu_subdev_set_fmt(struct v4l2_subdev *sd,
> >>                 fmt->format.height = clamp(fmt->format.height,
> >>                                            IPU3_INPUT_MIN_HEIGHT,
> >>                                            IPU3_INPUT_MAX_HEIGHT);
> >> +
> >> +               /* input less than 2.3MP, ask imgu to work with low freq */
> >> +               if ((fmt->format.width * fmt->format.height) < (2048 * 1152))
> >
> > Why 2048 * 1152 specifically if we just care about the number of
> > pixels? Also it's slightly more than 2.3Mpix (2.359296 Mpix) making
> > the comment inaccurate.
> 2048 *1152 is the smallest common 16:9/4:3 resolution that larger than
> 1080p, we try to use this resolution as the start point to make imgu
> work on high frequency.

I'm still not sure what's the reason for this particular value. What's
exactly the hardware specification for 200 MHz?

> >
> >> +                       imgu->low_power = true;
> >> +               else
> >> +                       imgu->low_power = false;
> >
> > There should be no need to store this, as we should have access to the
> > exact format when we start streaming. Could you move the check there?
> >
> > Also, we have 2 pipes. How do they play together?
> We want to guarantee 2 pipes can always work on each frequency, there is
> no precise calculation which can be used to make more finer granularity.

i'm not sure I follow. imgu->low_power is a variable common to both
pipes, but it can be changed from subdev_s_fmt() of each pipe
separately.

Consider this example:
- pipe 0 s_fmt 2048x1536 -> low_power = false;
- pipe 1 s_fmt 1024x768 -> low_power = truel

We end up with low_power despite the resolution on pipe 0 being higher
than the thershold.

Best regards,
Tomasz