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

[Bingbu Cao <bingbu.cao@linux.intel.com>]

On 8/16/19 3:07 PM, Tomasz Figa wrote:
> 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?
200MHz is the lowest frequency allowed by hardware, and we validate it
can work for current 1080p use cases. 450MHz is the recommend
frequency in spec.
> 
>>>
>>>> +                       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.
I change the behavior in v2, could you help review?
> 
> Best regards,
> Tomasz
>