Re: [PATCH] arm: msm: Add MSM IOMMU support.

From: Russell King - ARM Linux
Date: Fri Aug 06 2010 - 05:00:17 EST

On Fri, Aug 06, 2010 at 01:17:46AM -0700, stepanm@xxxxxxxxxxxxxx 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.


* 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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