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    SubjectRE: sysfs and power management


    >-----Original Message-----
    >From: ext Alan Cox [mailto:alan@linux.intel.com]
    >Sent: 03 November, 2010 11:45
    >To: Greg KH
    >Cc: Onkalo Samu.P (Nokia-MS/Tampere); ext Henrique de Moraes Holschuh;
    >Alan Cox; akpm@linux-foundation.org; linux-kernel@vger.kernel.org
    >Subject: Re: sysfs and power management
    >
    >On Mon, 1 Nov 2010 11:07:40 -0700
    >Greg KH <gregkh@suse.de> wrote:
    >
    >> On Mon, Nov 01, 2010 at 04:57:01PM +0000, Alan Cox wrote:
    >> > > I took a look to that. It seems that iio is more or less sysfs
    >> > > based. There are ring buffers and event device which are chardev
    >> > > based but still the data outside ring buffer and the control is
    >> > > sysfs based.
    >> >
    >> > IIO is sysfs dependant, heavyweight and makes no sense for some of
    >> > the sysfs based drivers. IIO is also staging based and Linus
    >> > already threw out the last attempt to unify these drivers sanely
    >> > with an ALS layer - which was smaller, cleaner and better !
    >>
    >> I think we need to revisit this issue again, before iio is merged to
    >> the main kernel tree. I've been totally ignoring the iio user/kernel
    >> api at the moment, waiting for things to settle down there
    >
    >Actually I think there is another way to do it cleanly
    >
    >Keep a flag per device (or per runtime pm struct of device)
    >
    >And on the open/close do
    >
    > if (runtime_pm on device && device has SYSFS_PM set)
    > pm_runtime_foo
    >
    >so that devices that need to be powered up to handle sysfs requests can
    >set a single flag and just work.

    That is one quite clean way.
    sysfs_ops still needs function pointer to device core function which does pm_runtime
    calls.
    And there is one drawback. Driver doesn't know about new users after the first one.
    It may want to refresh results whenever a new user appears. But that is probably not
    a big issue.

    -Samu








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