Date: Fri, 6 Aug 2010 09:59:41 +0100
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: stepanm@codeaurora.org
Cc: dwalker@codeaurora.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm: msm: Add MSM IOMMU support.
Message-ID: <20100806085941.GA15852@n2100.arm.linux.org.uk>
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On Fri, Aug 06, 2010 at 01:17:46AM -0700, stepanm@codeaurora.org wrote:
> Thank you for your comments. I will apply the fixes you have mentioned. I
> am flushing the cache when I update the page table because the page table
> lives in regular RAM that is mapped as cacheable on the CPU side, and in
> the default configuration the IOMMU reads the page table from RAM.

That's fine, but use the right function.

> So, I
> have put in the flush call to give the IOMMU a coherent view of the page
> tables. I realize it is more efficient to just flush that specific part of
> L2, but this is just the basic version of the driver and that optimization
> will be eventually put in.

Here, you're talking about L2 again, but your code only touches the L1
cache.  I think you're confused about caching.

> What did you mean by:
> > Any reason you can't have some kind of struct device instead?
> 
> Are you referring to the clock line? As far as I understand it, the kernel
> tracks the clocks by a string name, but I can look into it further.

No.

/**
 * clk_get - lookup and obtain a reference to a clock producer.
 * @dev: device for clock "consumer"
 * @id: clock comsumer ID
 *
 * Returns a struct clk corresponding to the clock producer, or
 * valid IS_ERR() condition containing errno.  The implementation
 * uses @dev and @id to determine the clock consumer, and thereby
 * the clock producer.  (IOW, @id may be identical strings, but
 * clk_get may return different clock producers depending on @dev.)

The intention is that 'id' is specific to each 'dev', and identifies
the connection on 'dev' that you want the clock for.  It's the
_consumer's_ name, nothing to do with the clock producer.

There's also clk_get_sys() if you don't have a struct device.
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