linux-kernel - Re: [PATCH 13/26] ARM: pxa: use correct _

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Date:	Sat, 8 Oct 2011 20:43:23 +0800
From:	Eric Miao <eric.y.miao@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Jason Chagas <jason.chagas@...vell.com>,
	Haojian Zhuang <haojian.zhuang@...vell.com>
Subject: Re: [PATCH 13/26] ARM: pxa: use correct __iomem annotations

On Fri, Oct 7, 2011 at 6:16 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Friday 07 October 2011, Eric Miao wrote:
>> > @@ -18,11 +24,11 @@
>> >  * peripherals on APB, let's count it into the ABP mapping area.
>> >  */
>> >  #define APB_PHYS_BASE          0xd4000000
>> > -#define APB_VIRT_BASE          0xfe000000
>> > +#define APB_VIRT_BASE          IOMEM(0xfe000000)
>>
>> To be honest, I'd really like to keep the *_VIRT_BASE definitions to be
>> type independent.
>>
>> And have the actual register definitions to be casted to void __iomem *
>> when being defined, e.g.
>>
>> #define APBC_REG(x)     IOMEM(APBC_VIRT_BASE + (x))
>>
>> #define APBC_UART1      APBC_REG(0x000)
>>
>> Arnd, do we have some standard guidelines on this for all SoCs
>> to follow? As I know, it's currently still being a mess.
>
> We don't have any formal guidelines yet, but I'd really love to get
> rid of all the arbitrary type casts to make use of the built-in
> type checking of the compiler and sparse. A virtual base address
> for registers is conventionally an __iomem pointer, so defining it
> as something else is completely bogus. I have started making patches
> for a number of platforms for this.
>
> Ideally we should have very little code directly using, but the fact
> is that they are there and we won't remove them all anytime soon, so
> we should at least use the correct types here.
>
> Another issue that goes together with this is that right now our
> readl/writel macros accept any input type (pointer, __iomem pointer,
> unsigned long, unsigned int), and I have a patch to make that stricter
> but that requires fixing up all the places where we do a
> readl(APBC_VIRT_BASE + x) that Russell mentioned.
>
> The only place where this requires adding extra type casts right now is
> the iotable setup, which I hope we can also fix eventually by splitting
> the static I/O mapping setup from other static mappings (MT_MEMORY,
> MT_MEMORY_NONCACHED, ...).

Sounds fair enough. Applied.
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