linux-kernel - Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)

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Date:	Thu, 7 Feb 2013 08:23:41 +0100
From:	Michal Simek <monstr@...str.eu>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Grant Likely <grant.likely@...retlab.ca>,
	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	dahinds@...rs.sourceforge.net
Subject: Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)_le16
 with generic iowrite(read)8/16(be)

2013/2/6 Geert Uytterhoeven <geert@...ux-m68k.org>:
> On Wed, Feb 6, 2013 at 6:40 PM, Michal Simek <monstr@...str.eu> wrote:
>> One question regarding to asm-generic/io.h about iowrite16be implementation
>>
>> #define iowrite16be(v, addr)   iowrite16(be16_to_cpu(v), (addr))
>> #define iowrite16(v, addr)      writew((v), (addr))
>> #define writew(b,addr) __raw_writew(__cpu_to_le16(b),addr)
>>
>> static inline void __raw_writew(u16 b, volatile void __iomem *addr)
>> {
>>         *(volatile u16 __force *) addr = b;
>> }
>>
>> How is this suppose to work on Big Endian?
>> be16_to_cpu(v) is (v)
>> and
>> __cpu_to_le16(b) is swab16(v)
>
> Yes.

But on native BE system ( I expect that v is in big endian)
iowrite16be(v, addr) should be just *(volatile u16 __force *) addr =
v; not *(volatile u16 __force *) addr = swab16(v);


>> On little
>> be16_to_cpu(v) is swab16(v)
>
> Yes.
>
>> and
>> __cpu_to_le16(swab(b)) is swab16(v)
>
> ???
>
> Don't you mean "__cpu_to_le16(b) is (b)"?

BTW: I took output value from the first line (be16_to_cpu(v) is swab16(v))

Grrr - on LE this code works. (I expect that v is in little endian)
iowrite16be(v, addr) is *(volatile u16 __force *) addr = swab16(v);


>> What I would expect is
>> #define iowrite16be(v, addr)   __raw_writew(__cpu_to_be16(v), addr)
>
> Indeed, it should be "__cpu_to_be16(v)" instead of "be16_to_cpu(v)".

What do you mean by that?

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform
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