[PATCH 21/23] ARM: add generic ioremap optimization by reusing static mappings

[Russell King - ARM Linux]

On Wed, Nov 16, 2011 at 12:48:39AM -0500, Nicolas Pitre wrote:
> @@ -201,12 +195,6 @@ void __iomem * __arm_ioremap_pfn_caller(unsigned long pfn,
>  	if (pfn >= 0x100000 && (__pfn_to_phys(pfn) & ~SUPERSECTION_MASK))
>  		return NULL;
>  
> -	/*
> -	 * Don't allow RAM to be mapped - this causes problems with ARMv6+
> -	 */
> -	if (WARN_ON(pfn_valid(pfn)))
> -		return NULL;
> -
>  	type = get_mem_type(mtype);
>  	if (!type)
>  		return NULL;
> @@ -216,6 +204,34 @@ void __iomem * __arm_ioremap_pfn_caller(unsigned long pfn,
>  	 */
>  	size = PAGE_ALIGN(offset + size);
>  
> +	/*
> +	 * Try to reuse one of the static mapping whenever possible.
> +	 */
> +	read_lock(&vmlist_lock);
> +	for (area = vmlist; area; area = area->next) {
> +		if (!size || (sizeof(phys_addr_t) == 4 && pfn >= 0x100000))
> +			break;
> +		if (!(area->flags & VM_ARM_STATIC_MAPPING))
> +			continue;
> +		if ((area->flags & VM_ARM_MTYPE_MASK) != VM_ARM_MTYPE(mtype))
> +			continue;
> +		if (__phys_to_pfn(area->phys_addr) > pfn ||
> +		    __pfn_to_phys(pfn) + size-1 > area->phys_addr + area->size-1)
> +			continue;
> +		/* we can drop the lock here as we know *area is static */
> +		read_unlock(&vmlist_lock);
> +		addr = (unsigned long)area->addr;
> +		addr += __pfn_to_phys(pfn) - area->phys_addr;
> +		return (void __iomem *) (offset + addr);
> +	}
> +	read_unlock(&vmlist_lock);
> +
> +	/*
> +	 * Don't allow RAM to be mapped - this causes problems with ARMv6+
> +	 */
> +	if (WARN_ON(pfn_valid(pfn)))
> +		return NULL;

Why are you moving this check?  System RAM should never end up in the
vmlist.