[PATCH 22/24] scsi: eesox: use __iomem pointers for MMIO

On Sat, Sep 15, 2012 at 10:30:43AM +0000, Arnd Bergmann wrote:

On Saturday 15 September 2012, Russell King - ARM Linux wrote:

quoted

On Sat, Sep 15, 2012 at 08:00:35AM +0000, Arnd Bergmann wrote:

quoted

On Friday 14 September 2012, Russell King - ARM Linux wrote:

quoted

On Fri, Sep 14, 2012 at 11:34:50PM +0200, Arnd Bergmann wrote:

quoted

ARM is moving to stricter checks on readl/write functions,
so we need to use the correct types everywhere.

There's nothing wrong with const iomem pointers.  If you think
otherwise, patch x86 not to use const in its accessor implementation
and watch the reaction:

#define build_mmio_read(name, size, type, reg, barrier) \
static inline type name(const volatile void __iomem *addr) \
{ type ret; asm volatile("mov" size " %1,%0":reg (ret) \
:"m" (*(volatile type __force *)addr) barrier); return ret; }

build_mmio_read(readb, "b", unsigned char, "=q", :"memory")
build_mmio_read(readw, "w", unsigned short, "=r", :"memory")
build_mmio_read(readl, "l", unsigned int, "=r", :"memory")

Ok, fair enough. Can you fold the patch below into 
"ARM: 7500/1: io: avoid writeback addressing modes for __raw_
accessors", or apply on top then?

No - const is not appropriate for the write accessors.  Again, this puts
us at odds with x86:

#define build_mmio_write(name, size, type, reg, barrier) \
static inline void name(type val, volatile void __iomem *addr) \
{ asm volatile("mov" size " %0,%1": :reg (val), \
"m" (*(volatile type __force *)addr) barrier); }

build_mmio_write(writeb, "b", unsigned char, "q", :"memory")
build_mmio_write(writew, "w", unsigned short, "r", :"memory")
build_mmio_write(writel, "l", unsigned int, "r", :"memory")

So, readl etc are all const volatile void __iomem *, but writel etc are
all volatile void __iomem *.

How they're defined on ARM after 7500/1 copies how they're defined on
x86.

Well, you have to make up your mind what you want. Right now, we get these
warnings in rpc_defconfig:

  Generating include/generated/mach-types.h
/home/arnd/linux-arm/drivers/net/ethernet/seeq/ether3.c: In function 'ether3_outb':
/home/arnd/linux-arm/drivers/net/ethernet/seeq/ether3.c:104:2: error: passing argument 2 of '__raw_writeb' discards 'const' qualifier from pointer target type [-Werror]
/home/arnd/linux-arm/arch/arm/include/asm/io.h:81:91: note: expected 'volatile void *' but argument is of type 'const void *'
/home/arnd/linux-arm/drivers/scsi/arm/eesox.c: In function 'eesoxscsi_buffer_out':
/home/arnd/linux-arm/drivers/scsi/arm/eesox.c:310:4: error: passing argument 2 of '__raw_writel' discards 'const' qualifier from pointer target type [-Werror]
/home/arnd/linux-arm/arch/arm/include/asm/io.h:88:91: note: expected 'volatile void *' but argument is of type 'const void *'
/home/arnd/linux-arm/drivers/scsi/arm/eesox.c:324:4: error: passing argument 2 of '__raw_writel' discards 'const' qualifier from pointer target type [-Werror]
/home/arnd/linux-arm/arch/arm/include/asm/io.h:88:91: note: expected 'volatile void *' but argument is of type 'const void *'
/home/arnd/linux-arm/drivers/scsi/arm/eesox.c:325:4: error: passing argument 2 of '__raw_writel' discards 'const' qualifier from pointer target type [-Werror]
/home/arnd/linux-arm/arch/arm/include/asm/io.h:88:91: note: expected 'volatile void *' but argument is of type 'const void *'

Either we allow drivers to write to const __iomem pointers or we don't. I
don't care which way we do it, but just saying both patches are wrong is
not very helpful.

In both of my replies, I've said "as x86 does".  We need to follow
x86's behaviour here, which is as I've quoted - it's not a matter
that "I need to make up my mind" - my mind is already well made up.
That is, we need to follow x86 here.

That is, const volatile void __iomem * for reads, and volatile void
__iomem * for writes.