From: Greg KH <greg@kroah.com>
To: Robert Schwebel <r.schwebel@pengutronix.de>
Cc: linuxppc-dev@ozlabs.org, Heiko Schocher <hs@denx.de>,
linux-kernel@vger.kernel.org, Detlev Zundel <dzu@denx.de>
Subject: Re: SYSFS: need a noncaching read
Date: Wed, 12 Sep 2007 03:01:23 -0700 [thread overview]
Message-ID: <20070912100123.GA23182@kroah.com> (raw)
In-Reply-To: <20070912053207.GH23573@pengutronix.de>
On Wed, Sep 12, 2007 at 07:32:07AM +0200, Robert Schwebel wrote:
> On Tue, Sep 11, 2007 at 11:43:17AM +0200, Heiko Schocher wrote:
> > I have developed a device driver and use the sysFS to export some
> > registers to userspace.
>
> Uuuh, uggly. Don't do that. Device drivers are there to abstract things,
> not to play around with registers from userspace.
>
> > I opened the sysFS File for one register and did some reads from this
> > File, but I alwas becoming the same value from the register, whats not
> > OK, because they are changing. So I found out that the sysFS caches
> > the reads ... :-(
>
> Yes, it does. What you can do is close()ing the file handle between
> accesses, which makes it work but is slow.
Do an lseek back to 0 and then re-read, you will get called in your
driver again.
Not that this is a good thing to do for this kind of thing, as others
have already said.
thanks,
greg k-h
WARNING: multiple messages have this Message-ID (diff)
From: Greg KH <greg@kroah.com>
To: Robert Schwebel <r.schwebel@pengutronix.de>
Cc: Heiko Schocher <hs@denx.de>,
linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
Detlev Zundel <dzu@denx.de>
Subject: Re: SYSFS: need a noncaching read
Date: Wed, 12 Sep 2007 03:01:23 -0700 [thread overview]
Message-ID: <20070912100123.GA23182@kroah.com> (raw)
In-Reply-To: <20070912053207.GH23573@pengutronix.de>
On Wed, Sep 12, 2007 at 07:32:07AM +0200, Robert Schwebel wrote:
> On Tue, Sep 11, 2007 at 11:43:17AM +0200, Heiko Schocher wrote:
> > I have developed a device driver and use the sysFS to export some
> > registers to userspace.
>
> Uuuh, uggly. Don't do that. Device drivers are there to abstract things,
> not to play around with registers from userspace.
>
> > I opened the sysFS File for one register and did some reads from this
> > File, but I alwas becoming the same value from the register, whats not
> > OK, because they are changing. So I found out that the sysFS caches
> > the reads ... :-(
>
> Yes, it does. What you can do is close()ing the file handle between
> accesses, which makes it work but is slow.
Do an lseek back to 0 and then re-read, you will get called in your
driver again.
Not that this is a good thing to do for this kind of thing, as others
have already said.
thanks,
greg k-h
next prev parent reply other threads:[~2007-09-12 10:01 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-11 9:43 SYSFS: need a noncaching read Heiko Schocher
2007-09-11 9:43 ` Heiko Schocher
2007-09-12 2:05 ` David Gibson
2007-09-12 2:05 ` David Gibson
2007-09-12 3:18 ` Michael Ellerman
2007-09-12 3:18 ` Michael Ellerman
2007-09-12 5:32 ` Robert Schwebel
2007-09-12 5:32 ` Robert Schwebel
2007-09-12 10:01 ` Greg KH [this message]
2007-09-12 10:01 ` Greg KH
2007-09-11 19:19 ` Nick Piggin
2007-09-11 19:19 ` Nick Piggin
2007-09-12 17:57 ` Neil Brown
2007-09-12 17:57 ` Neil Brown
2007-09-12 11:13 ` Heiko Schocher
2007-09-12 11:13 ` Heiko Schocher
2007-09-12 11:39 ` Greg KH
2007-09-12 11:39 ` Greg KH
2007-09-12 11:59 ` Heiko Schocher
2007-09-12 11:59 ` Heiko Schocher
2007-09-17 5:22 ` Tejun Heo
2007-09-17 5:22 ` Tejun Heo
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