linux-kernel - Re: [PATCH 15/17] fpga: dfl: fme: add power management support

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Message-ID: <20190417073654.GB23258@hao-dev>
Date:   Wed, 17 Apr 2019 15:36:54 +0800
From:   Wu Hao <hao.wu@...el.com>
To:     Alan Tull <atull@...nel.org>
Cc:     Moritz Fischer <mdf@...nel.org>, linux-fpga@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org, Luwei Kang <luwei.kang@...el.com>,
        Xu Yilun <yilun.xu@...el.com>
Subject: Re: [PATCH 15/17] fpga: dfl: fme: add power management support

On Mon, Apr 15, 2019 at 04:17:48PM -0500, Alan Tull wrote:
> On Thu, Apr 11, 2019 at 10:06 PM Wu Hao <hao.wu@...el.com> wrote:
> >
> > On Thu, Apr 11, 2019 at 03:07:35PM -0500, Alan Tull wrote:
> > > On Sun, Mar 24, 2019 at 10:24 PM Wu Hao <hao.wu@...el.com> wrote:
> > >
> > > Hi Hao,
> > >
> > > >
> > > > This patch adds support for power management private feature under
> > > > FPGA Management Engine (FME), sysfs interfaces are introduced for
> > > > different power management functions, users could use these sysfs
> > > > interface to get current number of consumed power, throttling
> > >
> > > How about
> > > s/number/measurement/
> > > ?
> >
> > Sounds better. : )
> >
> > >
> > > > thresholds, threshold status and other information, and configure
> > > > different value for throttling thresholds too.
> > > >
> > > > Signed-off-by: Luwei Kang <luwei.kang@...el.com>
> > > > Signed-off-by: Xu Yilun <yilun.xu@...el.com>
> > > > Signed-off-by: Wu Hao <hao.wu@...el.com>
> > > > ---
> > > >  Documentation/ABI/testing/sysfs-platform-dfl-fme |  56 +++++
> > > >  drivers/fpga/dfl-fme-main.c                      | 257 +++++++++++++++++++++++
> > > >  2 files changed, 313 insertions(+)
> > > >
> > > > diff --git a/Documentation/ABI/testing/sysfs-platform-dfl-fme b/Documentation/ABI/testing/sysfs-platform-dfl-fme
> > > > index d3aeb88..4b6448f 100644
> > > > --- a/Documentation/ABI/testing/sysfs-platform-dfl-fme
> > > > +++ b/Documentation/ABI/testing/sysfs-platform-dfl-fme
> > > > @@ -100,3 +100,59 @@ Description:       Read-only. Read this file to get the policy of temperature
> > > >                 threshold1. It only supports two value (policy):
> > > >                     0 - AP2 state (90% throttling)
> > > >                     1 - AP1 state (50% throttling)
> > > > +
> > > > +What:          /sys/bus/platform/devices/dfl-fme.0/power_mgmt/consumed
> > > > +Date:          March 2019
> > > > +KernelVersion:  5.2
> > > > +Contact:       Wu Hao <hao.wu@...el.com>
> > > > +Description:   Read-only. It returns current power consumed by FPGA.
> > >
> > > What are the units?
> > >
> > > > +
> > > > +What:          /sys/bus/platform/devices/dfl-fme.0/power_mgmt/threshold1
> > > > +Date:          March 2019
> > > > +KernelVersion:  5.2
> > > > +Contact:       Wu Hao <hao.wu@...el.com>
> > > > +Description:   Read-Write. Read/Write this file to get/set current power
> > > > +               threshold1 in Watts.
> > >
> > > Perhaps document error codes here and for threshold2 below.
> > >
> > > > +
> > > > +What:          /sys/bus/platform/devices/dfl-fme.0/power_mgmt/threshold2
> > > > +Date:          March 2019
> > > > +KernelVersion:  5.2
> > > > +Contact:       Wu Hao <hao.wu@...el.com>
> > > > +Description:   Read-Write. Read/Write this file to get/set current power
> > > > +               threshold2 in Watts.
> > > > +
> > > > +What:          /sys/bus/platform/devices/dfl-fme.0/power_mgmt/threshold1_status
> > > > +Date:          March 2019
> > > > +KernelVersion:  5.2
> > > > +Contact:       Wu Hao <hao.wu@...el.com>
> > > > +Description:   Read-only. It returns 1 if power consumption reaches the
> > > > +               threshold1, otherwise 0.
> > >
> > > I'm used to things like this requiring user to reset the status, so it
> > > may be worth making it explicit that it will return to zero if
> > > consumption drops below threshold if that's what's happening here.
> > > If it's correct, perhaps could just say something like 'returns 1 if
> > > power consumption is currently at or above threshold1, otherwise 0'
> > >
> > > > +
> > > > +What:          /sys/bus/platform/devices/dfl-fme.0/power_mgmt/threshold2_status
> > > > +Date:          March 2019
> > > > +KernelVersion:  5.2
> > > > +Contact:       Wu Hao <hao.wu@...el.com>
> > > > +Description:   Read-only. It returns 1 if power consumption reaches the
> > > > +               threshold2, otherwise 0.
> > >
> > > Same here.
> >
> > Sure, will fix all above comments in this sysfs doc.
> >
> > >
> > > > +
> > > > +What:          /sys/bus/platform/devices/dfl-fme.0/power_mgmt/ltr
> > > > +Date:          March 2019
> > > > +KernelVersion:  5.2
> > > > +Contact:       Wu Hao <hao.wu@...el.com>
> > > > +Description:   Read-only. Read this file to get current Latency Tolerance
> > > > +               Reporting (ltr) value, it's only valid for integrated
> > > > +               solution as it blocks CPU on low power state.
> > >
> > > If we're not on the integrated solution, it returns a value but it is
> > > not really real?
> >
> > Currently only integrated solution is implementing this private feature, other
> > devices e.g. Intel PAC card is not using this private feature, so user will
> > not see these sysfs interfaces at all.
> 
> OK then perhaps the "it's only valid for integrated solution as it
> blocks CPU on low power state" explanation doesn't need to be here and
> can lead to confusion.
> 

Sure, will fix it in the next version. Thanks!

Hao