[PATCH v2 0/3] fix memremap on ARM

[Ard Biesheuvel]

On 3 March 2016 at 18:27, Dan Williams <dan.j.williams at intel.com> wrote:
> On Thu, Mar 3, 2016 at 9:16 AM, Ard Biesheuvel
> <ard.biesheuvel at linaro.org> wrote:
>> On 3 March 2016 at 18:13, Russell King - ARM Linux
>> <linux at arm.linux.org.uk> wrote:
>>> On Thu, Mar 03, 2016 at 05:24:41PM +0100, Ard Biesheuvel wrote:
>>>> If there are no remaining objections, may I suggest that Dan takes
>>>> patch #1 and #2, and that I put the third patch into Russell's patch
>>>> system? The only strict ordering requirement is that #1 is merged
>>>> before #2 and #3 both hit mainline, and that is solved by taking #1
>>>> and #2 in order.
>>>
>>> How does the dependency between 1 and 3 get satisfied?  Your comment
>>> makes no sense to me.
>>>
>>
>> Patch #3 introduces a function arch_memremap_wb() on the ARM side
>> which will never get called unless patch #2 is also merged. Once both
>> #2 and #3 are in, the memremap() call that #1 reverts will use
>> MT_MEMORY_RW attributes rather than MT_DEVICE_CACHED, so #1 needs to
>> go first, but #2 and #3 can go in in either order.
>>
>> In other words, there are no build dependencies between the patches,
>> but to prevent pxa2xx-flash from using MT_MEMORY_RW attributes, it
>> needs to go in before #2
>
> Can we add a new MEMREMAP_ type for this case so that we don't need to
> keep carrying the confusing ioremap_cache() which means different
> things to different archs and silently falls back to uncached on some
> archs.

Actually, I don't think so. Unifying ioremap_cache() between
architectures was a mistake to begin with, since I/O mapping
attributes vary so wildly between architectures, and there are very
few drivers that depend on such specific behavior that actually need
to be built for multiple architectures.

So I think your memremap() is a fantastic idea, considering the
widespread abuse of ioremap_cache(), also in common code. But removing
it altogether to replace it with something that looks generic but
never is, is just repeating the same mistake imo.