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

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Date:	Wed, 6 Feb 2013 17:21:37 +0100
From:	Michal Simek <monstr@...str.eu>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Arnd Bergmann <arnd@...db.de>,
	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>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	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 Grant Likely <grant.likely@...retlab.ca>:
> On Tue, Feb 5, 2013 at 3:12 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> On Tuesday 05 February 2013 18:03:31 Alexey Brodkin wrote:
>>> The Xilinx System ACE Compact Flash chip is a true little-endian device
>>> and the PLB is a big-endian bus. Therefore the XPS System ACE Interface
>>> Controller will do a bit-swap in each byte when connecting the PLB data
>>> bus to the System ACE data bus as shown in Table 2.
>>>
>>> Note however, that the XPS System ACE Interface Controller does not
>>> perform the byte swapping necessary to interface to a little-endian
>>> device when configured to use 16-bit mode. Therefore, the software
>>> drivers provided for this core will perform the necessary byte-swapping
>>> to correctly interface to the Xilinx System ACE Compact Flash chip as
>>> shown in Table 3.
>>
>> Ok. In this case, I would recommend making the default for this driver
>> little-endian, and adding a quirk for broken hardware bridges like the
>> one you cited to have a mixed-endian mode if configured so at compile
>> time.
>>
>> It seems that on all normal platforms, this device should behave as
>> little-endian, while the Xilinx bridge can be either big-endian
>> or little-endian, depending on whether it is used in 8-bit or 16-bit
>> mode, so if we are using this, it cannot be known at compile time.
>
> The driver already handles this. It has three sets of accessors;
> 8-bit, 16-bit LE and 16-bit BE *and* when doing 16-bit it figures out
> on its own which set to use at runtime. There is nothing controversial
> here. The only problem is that the driver is currently using in_/out_
> IO accessors instead of ioread/iowrite variants.

I have looked at the patches from more practical side and I have tested it on
microblaze big endian in 16bit mode and I have found that sysace driver
stop to work.
After that I have looked at ioread/iowrite microblaze implementation
and implementation of that functions is wrong.
I have fixed it but looking at using asm-generic/io.h for microblaze.

I will do more tests and let you know.

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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