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

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Date:	Tue, 5 Feb 2013 11:45:55 +0100
From:	Michal Simek <monstr@...str.eu>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	linux-kernel@...r.kernel.org, grant.likely@...retlab.ca,
	benh@...nel.crashing.org, alan@...rguk.ukuu.org.uk,
	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)

2013/2/4 Arnd Bergmann <arnd@...db.de>:
> On Monday 04 February 2013, Michal Simek wrote:
>> >
>> > and select the CONFIG_FOO_BIG_ENDIAN and CONFIG_FOO_LITTLE_ENDIAN
>> > symbols in Kconfig based on the system you are building for.
>>
>> Using CONFIG_FOO_BIG/LITTLE is not good because it is just another
>> Kconfig option.
>> You can easily detect it at runtime and for dedicated hw with fixed
>> endians you can just
>> handle it in the driver and don't care about global setting.
>
> The configuration option should not be visible, so it's
> not something a user would have to worry about. It's just
> sometimes nicer to express the configuration of the platform
> in terms of Kconfig syntax than it is in C code if you have
> complex platform dependencies.
>
>> > This of course gets further complicated if you require different
>> > accessors per architecture, like ARM wanting readl or ioread32
>> > and PowerPC wanting in_le32 for a little-endian SoC component.
>>
>> FYI: I have got two responses on linux-arch from Alan
>> "Set the pointers up and pass them as data with your platform device, that
>> way the function definitions are buried in your platform code where they
>> depend."
>>
>> and Geert:
>> "Or embed a struct io_ops * in struct device, to be set up by the bus driver?
>>
>> Wasn't David Hinds working on something like this in the context of PCMCIA
>> a few decades ago?"
>>
>> Based on their suggestions one way can be to pass it through void *platform_data
>> which is probably not the best and then which make more sense to me is to extend
>> struct dev_archdata archdata to add there native read/write functions.
>>
>> What do you think?
>
> I worry a little about code size if we have a lot of drivers that go
> from one instruction to an indirect function call for each readl/writel.
> Using platform_data ss also something that does not work too well with
> device tree based platform configuration, which tries hard to leave
> all run-time configuration inside of the driver.

As you have seen from the list of architectures all of them uses device tree.

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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