linux-kernel - Re: [RFC PATCHv3 1/4] drivers/otp: add initial support for OTP memory

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Message-ID: <20110325225523.GW3130@pulham.picochip.com>
Date:	Fri, 25 Mar 2011 22:55:23 +0000
From:	Jamie Iles <jamie@...ieiles.com>
To:	Mike Frysinger <vapier@...too.org>
Cc:	Jamie Iles <jamie@...ieiles.com>, linux-kernel@...r.kernel.org,
	gregkh@...e.de
Subject: Re: [RFC PATCHv3 1/4] drivers/otp: add initial support for OTP memory

On Fri, Mar 25, 2011 at 06:50:36PM -0400, Mike Frysinger wrote:
> On Fri, Mar 25, 2011 at 18:47, Jamie Iles wrote:
> > On Fri, Mar 25, 2011 at 05:58:05PM -0400, Mike Frysinger wrote:
> >> On Fri, Mar 25, 2011 at 13:14, Jamie Iles wrote:
> >> > +/* We'll allow OTP devices to be named otpa-otpz. */
> >> > +#define MAX_OTP_DEVICES                26
> >>
> >> mmm is that still true ?
> >
> > I think so - the actual devices should be otpa-otpz, but when you
> > register regions they could be otpa1, otpa2, otpb1, otpb2 etc.
> >
> >>
> >> > +static unsigned long registered_otp_map[BITS_TO_LONGS(MAX_OTP_DEVICES)];
> >> > +static DEFINE_MUTEX(otp_register_mutex);
> >>
> >> do we really need this ?  if we let the minor number dictate
> >> availability, then we can increment until that errors/wraps, and we
> >> dont need to do any tracking ...
> >
> > OK, so it would be nice to get rid of this but afaict we still need to
> > do some accounting of available minor numbers in the range that we've
> > allocated.  We could do a simple increment % 255 for the minor number
> > but if OTP devices are removed at runtime then that may get fragmented
> > and we would need to do retries of device_register() which feels a bit
> > too easy to mess up.
> >
> > Certainly allocating one major number for OTP devices then allocating
> > the minors one by one would be much better than what I have now.
> >
> > We probably also want it so that if you remove the OTP device that has
> > had regions called otpaN then reinsert it they doesn't suddenly become
> > otpbN.
> 
> yeah that's true.  guess i'll leave it be then ;).

OK, but it still might be worth pruning it down to a single major number 
or is that something worth doing later on if it becomes needed?

> whatever naming is picked in /dev/ should match the stuff in /sys/ btw ...

I think that's working ok.  On my system I have:

	/sys/bus/otp/devices/otpa/otpa1/
	/sys/bus/otp/devices/otpa/otpa2/

and

	/dev/otpa1
	/dev/otpa2

Jamie
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