Date:   Mon, 9 Nov 2020 13:45:45 +0000
From:   zhangqilong <zhangqilong3@...wei.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
CC:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "fugang.duan@....com" <fugang.duan@....com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: 答复: [PATCH 1/2] PM: runtime: Add a general runtime get sync operation to deal with usage counter

Hi,

> 
> On Mon, Nov 9, 2020 at 2:24 PM zhangqilong <zhangqilong3@...wei.com>
> wrote:
> >
> > Hi
> > >
> > > On Mon, Nov 9, 2020 at 9:05 AM Zhang Qilong
> > > <zhangqilong3@...wei.com>
> > > wrote:
> > > >
> > > > In many case, we need to check return value of
> > > > pm_runtime_get_sync, but it brings a trouble to the usage counter
> > > > processing. Many callers forget to decrease the usage counter when
> > > > it failed. It has been discussed a lot[0][1]. So we add a function
> > > > to deal with the usage counter for better coding.
> > > >
> > > > [0]https://lkml.org/lkml/2020/6/14/88
> > > > [1]https://patchwork.ozlabs.org/project/linux-tegra/patch/20200520
> > > > 0951 48.10995-1-dinghao.liu@....edu.cn/
> > > > Signed-off-by: Zhang Qilong <zhangqilong3@...wei.com>
> > > > ---
> > > >  include/linux/pm_runtime.h | 32
> ++++++++++++++++++++++++++++++++
> > > >  1 file changed, 32 insertions(+)
> > > >
> > > > diff --git a/include/linux/pm_runtime.h
> > > > b/include/linux/pm_runtime.h index 4b708f4e8eed..2b0af5b1dffd
> > > > 100644
> > > > --- a/include/linux/pm_runtime.h
> > > > +++ b/include/linux/pm_runtime.h
> > > > @@ -386,6 +386,38 @@ static inline int pm_runtime_get_sync(struct
> > > > device
> > > *dev)
> > > >         return __pm_runtime_resume(dev, RPM_GET_PUT);  }
> > > >
> > > > +/**
> > > > + * gene_pm_runtime_get_sync - Bump up usage counter of a device
> > > > +and
> > > resume it.
> > > > + * @dev: Target device.
> > >
> > > The force argument is not documented.
> >
> > (1) Good catch, I will add it in next version.
> >
> > >
> > > > + *
> > > > + * Increase runtime PM usage counter of @dev first, and carry out
> > > > + runtime-resume
> > > > + * of it synchronously. If __pm_runtime_resume return negative
> > > > + value(device is in
> > > > + * error state) or return positive value(the runtime of device is
> > > > + already active)
> > > > + * with force is true, it need decrease the usage counter of the
> > > > + device when
> > > > + * return.
> > > > + *
> > > > + * The possible return values of this function is zero or negative value.
> > > > + * zero:
> > > > + *    - it means success and the status will store the resume operation
> > > status
> > > > + *      if needed, the runtime PM usage counter of @dev remains
> > > incremented.
> > > > + * negative:
> > > > + *    - it means failure and the runtime PM usage counter of @dev has
> > > been
> > > > + *      decreased.
> > > > + * positive:
> > > > + *    - it means the runtime of the device is already active before that.
> If
> > > > + *      caller set force to true, we still need to decrease the usage
> > > counter.
> > >
> > > Why is this needed?
> >
> > (2) If caller set force, it means caller will return even the device
> > has already been active (__pm_runtime_resume return positive value)
> > after calling gene_pm_runtime_get_sync, we still need to decrease the
> usage count.
> 
> But who needs this?
> 
> I don't think that it is a good idea to complicate the API this way.

The callers like:
ret = pm_runtime_get_sync(dev);
if (ret) {
	...
	return (xxx);
}
drivers/spi/spi-img-spfi.c:734 img_spfi_resume() warn: pm_runtime_get_sync() also returns 1 on success
drivers/mfd/arizona-core.c:49 arizona_clk32k_enable() warn: pm_runtime_get_sync() also returns 1 on success
drivers/usb/dwc3/dwc3-pci.c:212 dwc3_pci_resume_work() warn: pm_runtime_get_sync() also returns 1 on success
drivers/input/keyboard/omap4-keypad.c:279 omap4_keypad_probe() warn: pm_runtime_get_sync() also returns 1 on success
drivers/gpu/drm/vc4/vc4_dsi.c:839 vc4_dsi_encoder_enable() warn: pm_runtime_get_sync() also returns 1 on success
drivers/gpu/drm/i915/selftests/mock_gem_device.c:157 mock_gem_device() warn: 'pm_runtime_get_sync(&pdev->dev)' returns positive and negative
drivers/watchdog/rti_wdt.c:230 rti_wdt_probe() warn: pm_runtime_get_sync() also returns 1 on success
drivers/media/platform/exynos4-is/mipi-csis.c:513 s5pcsis_s_stream() warn: pm_runtime_get_sync() also returns 1 on success
drivers/media/platform/mtk-vcodec/mtk_vcodec_dec_pm.c:89 mtk_vcodec_dec_pw_on() warn: pm_runtime_get_sync() also returns 1 on success
drivers/media/platform/ti-vpe/cal.c:794 cal_probe() warn: pm_runtime_get_sync() also returns 1 on success
drivers/media/platform/ti-vpe/vpe.c:2478 vpe_runtime_get() warn: pm_runtime_get_sync() also returns 1 on success
drivers/media/i2c/smiapp/smiapp-core.c:1529 smiapp_pm_get_init() warn: pm_runtime_get_sync() also returns 1 on success
...
they need it to simplify the function.

If we only want to simplify like
ret = pm_runtime_get_sync(dev);
if (ret < 0) {
	...
	Return (xxx)
}
The parameter force could be removed.

Thanks,
Zhang

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