linux-kernel - Re: [PATCH][v2] PM / sysfs: Expose suspend resume driver flags in sysfs

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Message-ID: <20201022185320.GA8811@chenyu-office.sh.intel.com>
Date:   Fri, 23 Oct 2020 02:53:20 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][v2] PM / sysfs: Expose suspend resume driver flags in
 sysfs

Hi Andy,
On Thu, Oct 22, 2020 at 04:36:25PM +0300, Andy Shevchenko wrote:
> On Thu, Oct 22, 2020 at 12:24 PM Chen Yu <yu.c.chen@...el.com> wrote:
> >
> > Currently there are 4 driver flags to control system suspend/resume
> > behavior: DPM_FLAG_NO_DIRECT_COMPLETE, DPM_FLAG_SMART_PREPARE,
> > DPM_FLAG_SMART_SUSPEND and DPM_FLAG_MAY_SKIP_RESUME. Make these flags
> > visible in sysfs as read-only to get a brief understanding of the
> > expected behavior of each device during suspend/resume, so as to
> > facilitate suspend/resume debugging/tuning.
> >
> > For example:
> > /sys/devices/pci0000:00/0000:00:15.1/power/driver_flags:4
> > (DPM_FLAG_SMART_SUSPEND)
> >
> > /sys/devices/pci0000:00/0000:00:07.3/power/driver_flags:5
> > (DPM_FLAG_NO_DIRECT_COMPLETE | DPM_FLAG_SMART_SUSPEND)
> 
> ...
> 
> > +What:          /sys/devices/.../power/driver_flags
> > +Date:          October 2020
> > +Contact:       Chen Yu <yu.c.chen@...el.com>
> > +Description:
> > +               The /sys/devices/.../driver_flags attribute contains the driver
> > +               flags to control system suspend/resume. The flag is a combination
> > +               of DPM_FLAG_NO_DIRECT_COMPLETE, DPM_FLAG_SMART_PREPARE,
> > +               DPM_FLAG_SMART_SUSPEND and DPM_FLAG_MAY_SKIP_RESUME, or 0 if the
> > +               driver has not set any flag.
> 
> > This attribute is read-only. If
> > +               CONFIG_PM_ADVANCED_DEBUG is not set this attribute is empty.
> 
> Which makes me wonder why we even expose this if the above is not set.
> 
> ...
> 
It will not be exposed if the config is disabled. 'empty' means
'not present' I think.
> > +static struct attribute *pm_driver_flags_attrs[] = {
> > +#ifdef CONFIG_PM_ADVANCED_DEBUG
> > +#ifdef CONFIG_PM_SLEEP
> > +       &dev_attr_driver_flags.attr,
> > +#endif
> > +#endif
> 
> > +       NULL,
> 
> No comma here, please. I think I commented on this internally.
> 
Sorry I misunderstood your point previously, I can change in next
version. But might need to wait for Greg to decide if this item
should be exposed or not first.

Thanks,
Chenyu
> > +};
> 
> -- 
> With Best Regards,
> Andy Shevchenko