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

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Message-ID: <CADysL2bp08WP798_MvUJthGi9ACySDE=Dc_BM9Vd0A=YcKpm+Q@mail.gmail.com>
Date:	Thu, 11 Aug 2011 14:28:39 -0500
From:	"Gupta, Ramesh" <grgupta@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
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
Subject: Re: [PATCH] OMAP: iommu flush page table entries from L1 and L2 cache

Hi Russel,


On Thu, Apr 28, 2011 at 11:48 AM, Gupta, Ramesh <grgupta@...com> wrote:
> Hi Russel,
>
> On Thu, Apr 28, 2011 at 8:40 AM, Russell King - ARM Linux
> <linux@....linux.org.uk> wrote:
>> 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)...

my apologies for a late mail on this topic.

do you think of any other requirements for this new API?

Could we use the existing dmac_flush_range(), outer_flush_range()
for this purpose instead of a new API?

I see a comment in the arch/arm/include/asm/cacheflush.h
for  _not_ to use these APIs directly, but I am not really understand
the reason for that.

I would appreciate any inputs on this.

thank you and regards
Ramesh Gupta G
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