linux-kernel - Re: [PATCH 0/5] mfd: replace IORESOURCE_IO by IORESOURCE

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Message-ID: <20120807155001.GL24257@flint.arm.linux.org.uk>
Date:	Tue, 7 Aug 2012 16:50:02 +0100
From:	Russell King <rmk@....linux.org.uk>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Arnd Bergmann <arnd@...db.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	sameo@...ux.intel.com, rpurdie@...ys.net, bryan.wu@...onical.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] mfd: replace IORESOURCE_IO by IORESOURCE_MEM

On Tue, Aug 07, 2012 at 04:45:55PM +0100, Alan Cox wrote:
> >  #define IORESOURCE_TYPE_BITS	0x00001f00	/* Resource type */
> >  #define IORESOURCE_IO		0x00000100
> >  #define IORESOURCE_MEM		0x00000200
> > +#define IORESOURCE_FOO		0x00000300
> 
> These are bit masks and checked as such in many places. This makes no
> sense at all.

Correct, but nowhere are they checked as masks in the platform
device/driver code nor the MFD driver code.  Here's the relevant
extracts from the platform driver code:

struct resource *platform_get_resource(struct platform_device *dev,
                                       unsigned int type, unsigned int num)
{
        int i;

        for (i = 0; i < dev->num_resources; i++) {
                struct resource *r = &dev->resource[i];

                if (type == resource_type(r) && num-- == 0)
                        return r;
        }
        return NULL;
}

...
                        if (resource_type(r) == IORESOURCE_MEM)
                                p = &iomem_resource;
                        else if (resource_type(r) == IORESOURCE_IO)
                                p = &ioport_resource;

This is modern code, written using the accessors provided in ioport.h.

resource_type() is defined as:

static inline unsigned long resource_type(const struct resource *res)
{
        return res->flags & IORESOURCE_TYPE_BITS;
}

So, provided these don't leak outside of the platform and the affected
MFD drivers, what the rest of the kernel does doesn't matter.

> Moving to IO_RESOURCE_TYPE() being 0-31 values might be smart but its a
> massive all kernel change.

Only if we want to change the existing numbering _or_ propagate them
outside of platform devices etc, and when that happens that's the time
to start fixing stuff one subsystem at a time.

Of course, if the above helper was being used, we'd already be set.

I don't see that as a blocker to its local use, contained completely
within the MFD and platform device subsystems.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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