[PATCH v2 0/3] fix memremap on ARM

[Dan Williams]

On Thu, Mar 3, 2016 at 9:30 AM, Ard Biesheuvel
<ard.biesheuvel at linaro.org> wrote:
> 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.

I'm not suggesting it be a generic flag.  I.e. something like
MEMREMAP_ARM_ that explicitly documents that this driver has arch
specific mapping dependencies.  That request type will fail on any
arch that does not implement MEMREMAP_ARM_ support.