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

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Message-ID: <BANLkTikKnE-9WncNCADKfZVqkP1LFPYeXA@mail.gmail.com>
Date:	Thu, 28 Apr 2011 11:48:15 -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,
	Hari Kanigeri <h-kanigeri2@...com>
Subject: Re: [PATCH] OMAP: iommu flush page table entries from L1 and L2 cache

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)...

I agree with you, right now these functions are taking only start and
end arguments but
we can pass a struct deivice to these functions.

thank you and regards
Ramesh Gupta G
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