linux-kernel - Re: [PATCH 1/2] powerpc/iommu: expose IOMMU page shift

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Message-ID: <20151012160352.GA24212@linux.vnet.ibm.com>
Date:	Mon, 12 Oct 2015 09:03:52 -0700
From:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
To:	David Gibson <david@...son.dropbear.id.au>
Cc:	Matthew Wilcox <willy@...ux.intel.com>,
	Keith Busch <keith.busch@...el.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Alexey Kardashevskiy <aik@...abs.ru>,
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 1/2] powerpc/iommu: expose IOMMU page shift

On 06.10.2015 [14:19:43 +1100], David Gibson wrote:
> On Fri, Oct 02, 2015 at 10:18:00AM -0700, Nishanth Aravamudan wrote:
> > We will leverage this macro in the NVMe driver, which needs to know the
> > configured IOMMU page shift to properly configure its device's page
> > size.
> > 
> > Signed-off-by: Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
> > 
> > ---
> > Given this is available, it seems reasonable to expose -- and it doesn't
> > really make sense to make the driver do a log2 call on the existing
> > IOMMU_PAGE_SIZE() value.
> > 
> > diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> > index ca18cff..6fdf857 100644
> > --- a/arch/powerpc/include/asm/iommu.h
> > +++ b/arch/powerpc/include/asm/iommu.h
> > @@ -36,6 +36,7 @@
> >  #define IOMMU_PAGE_MASK_4K       (~((1 << IOMMU_PAGE_SHIFT_4K) - 1))
> >  #define IOMMU_PAGE_ALIGN_4K(addr) _ALIGN_UP(addr, IOMMU_PAGE_SIZE_4K)
> >  
> > +#define IOMMU_PAGE_SHIFT(tblptr) (tblptr)->it_page_shift
> >  #define IOMMU_PAGE_SIZE(tblptr) (ASM_CONST(1) << (tblptr)->it_page_shift)
> 
> Seems like it would be a touch safer to alter IOMMU_PAGE_SIZE so it
> uses the new IOMMU_PAGE_SHIFT macro.

Yes absolutely! Sorry, I initially didn't add the first macro, so didn't
think that through. Will update.

-Nish

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