linux-kernel - Re: [RFC/RFT 01/10] i2c: add 'is_suspended' flag for i2c adapters

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Date:   Wed, 19 Dec 2018 17:31:15 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Peter Rosin <peda@...ntia.se>, Hans de Goede <hdegoede@...hat.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC/RFT 01/10] i2c: add 'is_suspended' flag for i2c adapters

On Wed, Dec 19, 2018 at 10:39:05AM +0100, Geert Uytterhoeven wrote:
> Hi Wolfram,
> 
> On Wed, Dec 19, 2018 at 12:34 AM Wolfram Sang <wsa@...-dreams.de> wrote:
> > > > +   unsigned int is_suspended:1;    /* owned by the I2C core */
> > >
> > > When more stuff is added to this bit field (which always happens at
> > > some point) updates to all members of the bit field will have to use
> > > the same root-adapter-locking, or we will suffer from RMW-races. So
> > > this feels like an invitation for future disaster. Maybe a comment
> > > about that to remind our future selves? Or perhaps the bit field
> > > should be avoided altogether?
> >
> > Changed to bool. Thanks!
> 
> Does that help, given bool is smaller than the CPUs word size?
> Is it Alpha that cannot do atomic operations on bytes?

Yup, I overestimated bools :( I guess good old

unsigned long locked_flags;
#define <PREFIX>_IS_SUSPENDED	0

set_bit(), clear_bit(), and test_bit() is it then.


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