linux-kernel - Re: [PATCH] OMAP: iommu flush page table entries from L1 and L2 cache

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Message-ID: <20110428134055.GA19709@n2100.arm.linux.org.uk>
Date:	Thu, 28 Apr 2011 14:40:55 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	"Gupta, Ramesh" <grgupta@...com>
Cc:	Fernando Guzman Lugo <fernando.lugo@...com>,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, tony@...mide.com,
	Hari Kanigeri <h-kanigeri2@...com>
Subject: Re: [PATCH] OMAP: iommu flush page table entries from L1 and L2
	cache

On Fri, Apr 15, 2011 at 06:26:40AM -0500, Gupta, Ramesh wrote:
> Russell,
> 
> On Thu, Apr 14, 2011 at 5:30 PM, Russell King - ARM Linux
> <linux@....linux.org.uk> wrote:
> > On Thu, Apr 14, 2011 at 04:52:48PM -0500, Fernando Guzman Lugo wrote:
> >> From: Ramesh Gupta <grgupta@...com>
> >>
> >> This patch is to flush the iommu page table entries from L1 and L2
> >> caches using dma_map_single. This also simplifies the implementation
> >> by removing the functions  flush_iopgd_range/flush_iopte_range.
> >
> > No.  This usage is just wrong.  If you're going to use the DMA API then
> > unmap it, otherwise the DMA API debugging will go awol.
> >
> 
> Thank you for the comments, this particular memory is always a write
> from the A9 for MMU programming and
> only read from the slave processor, that is the reason for not calling
> the unmap. I can re-look into the changes to call
> unmap in a proper way as this impacts the DMA API.
> Are there any other ways to perform only flush the memory from L1/L2 caches?

We _could_ invent a new API to deal with this, which is probably going
to be far better in the longer term for page table based iommus.  That's
going to need some thought - eg, do we need to pass a struct device
argument for the iommu cache flushing so we know whether we need to flush
or not (eg, if we have cache coherent iommus)...
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