[RFC PATCH 1/2] arm: introduce arch_ioremap and arch_iounmap function pointer

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Sun, May 22, 2011 at 11:04:39AM +0200, Jean-Christophe PLAGNIOL-VILLARD wrote:
> today we define it at runtime via __arch_ioremap and __arch_iounmap
> 
> this PATH will allow to overwrite the default ioremap at runtime
> to be able to compile multiple soc in the same kernel

This is buggy.

> diff --git a/arch/arm/mm/ioremap.c b/arch/arm/mm/ioremap.c
> index ab50627..40ef390 100644
> --- a/arch/arm/mm/ioremap.c
> +++ b/arch/arm/mm/ioremap.c
> @@ -281,9 +281,15 @@ __arm_ioremap_pfn(unsigned long pfn, unsigned long offset, size_t size,
>  }
>  EXPORT_SYMBOL(__arm_ioremap_pfn);
>  
> +void __iomem* (*arch_ioremap)(unsigned long p, size_t size, unsigned int type);
> +void (*arch_iounmap)(volatile void __iomem *addr);
> +
>  void __iomem *
>  __arm_ioremap(unsigned long phys_addr, size_t size, unsigned int mtype)
>  {
> +	if (arch_ioremap)
> +		return arch_ioremap(phys_addr, size, mtype);
> +

Some SoCs call __arm_ioremap() from their ioremap() implementation, so
making this hook results in infinite function recursion if you try to
set this to their ioremap() implementation.

>  void __iounmap(volatile void __iomem *io_addr)
>  {
> -	void *addr = (void *)(PAGE_MASK & (unsigned long)io_addr);
> +	void *addr;
>  #ifndef CONFIG_SMP
>  	struct vm_struct **p, *tmp;
> +#endif
>  
> +	if (arch_iounmap) {
> +		arch_iounmap(io_addr);
> +		return;
> +	}

And on OMAP, for similar reasons, this will also be infinite function
recursion:

void omap_iounmap(volatile void __iomem *addr)
{
        unsigned long virt = (unsigned long)addr;

        if (virt >= VMALLOC_START && virt < VMALLOC_END)
                __iounmap(addr);
}

So you'll end up with a call to iounmap() calling __iounmap() which then
calls omap_iounmap(), which then calls __iounmap()...