linux-kernel - Re: [PATCH] ARM: mm: clean-up in order to reduce to call kmap_high

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Date:	Fri, 8 Mar 2013 09:51:17 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Nicolas Pitre <nico@...aro.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: mm: clean-up in order to reduce to call
 kmap_high_get()

Hello, Russell.

On Thu, Mar 07, 2013 at 01:26:23PM +0000, Russell King - ARM Linux wrote:
> On Mon, Mar 04, 2013 at 01:50:09PM +0900, Joonsoo Kim wrote:
> > In kmap_atomic(), kmap_high_get() is invoked for checking already
> > mapped area. In __flush_dcache_page() and dma_cache_maint_page(),
> > we explicitly call kmap_high_get() before kmap_atomic()
> > when cache_is_vipt(), so kmap_high_get() can be invoked twice.
> > This is useless operation, so remove one.
> > 
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> > 
> > diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> > index c7e3759..b7711be 100644
> > --- a/arch/arm/mm/dma-mapping.c
> > +++ b/arch/arm/mm/dma-mapping.c
> > @@ -822,16 +822,16 @@ static void dma_cache_maint_page(struct page *page, unsigned long offset,
> >  		if (PageHighMem(page)) {
> >  			if (len + offset > PAGE_SIZE)
> >  				len = PAGE_SIZE - offset;
> > -			vaddr = kmap_high_get(page);
> > -			if (vaddr) {
> > -				vaddr += offset;
> > -				op(vaddr, len, dir);
> > -				kunmap_high(page);
> > -			} else if (cache_is_vipt()) {
> > -				/* unmapped pages might still be cached */
> > +			if (cache_is_vipt()) {
> 
> This should be:
> 			if (cache_is_vipt_nonaliasing())
> 
> to make it _explicit_ that this technique is only for non-aliasing VIPT
> caches (this doesn't work on any other of our cache types.)  Yes, I
> know we don't support highmem with VIPT aliasing caches - but still,
> we should ensure that this is self-documented in this code.
> 
> Same for arch/arm/mm/flush.c

Okay. I will re-work and will send v2 soon.

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