Re: [RFC] introduce ioremap() and dev_ioremap_resource()

[Sascha Hauer <s.hauer@pengutronix.de>]

On Fri, Dec 19, 2014 at 01:32:37AM +0300, Antony Pavlov wrote:
> The commit
> 
>     commit 0d7a21334536cb36b3c9b64d868acc55aec41332
>     Author: Antony Pavlov <antonynpavlov@gmail.com>
>     Date:   Wed Sep 10 11:42:19 2014 +0400
> 
>         MIPS: dts: use physical addresses (as Linux does)
> 
>         With IOMEM() adapted for MIPS we can use physical addresses
>         in device tree reg property.
> 
> is premature. Current device tree files unusable on real hardware.
>                           I'M SO SORRY!
> The patch was tested on qemu, but qemu malta board is tolerant
> of using physical addresses for accesing to device. Real hardware
> can throw an exception in this situation.
> 
> Additional physical address to virtual address translation on MIPS is needed.
> 
> This commit demonstrate a possible (but not very good) solution.
> This solution is copied-and-pasted from linux kernel.
> In linux drivers use devm_ioremap_resource() function, so
> the patch just replicates similar dev_ioremap_resource() function.
> 
> Changing dev_request_mem_region() to dev_ioremap_resource()
> is not a very good idea because there are too many dev_request_mem_region()
> in barebox sources
> 
>     barebox$ git grep dev_request_mem_region | wc -l
>     197
> 
> moreover dev_ioremap_resource() has the second 'struct resource *res'
> argument, so additional dev_get_resource() is needed.
> 
> Can we insert ioremap() into dev_request_mem_region() directly?
> (we also can use already existion IOMEM() macro instead of linux' ioremap()).

I'm not sure if it's a good idea to put that behind some standard
lookingioremap() call, because its behaviour is not standard.

I'm also fine with adding some

#ifdef CONFIG_MIPS
	return mips_iomem(res->start);
#else
	return (void __force __iomem *)res->start;
#endif

At least this makes explicit that MIPS has a very special handling.

Sascha

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