RE: [PATCH/RFC] iommu/dma: Per-domain flag to control size-alignment

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Hi Robin, Magnus,

> -----Original Message-----
> From: Robin Murphy
> Sent: Saturday, January 28, 2017 2:38 AM
> 
> Hi Magnus,
> 
> On 27/01/17 06:24, Magnus Damm wrote:
> > From: Magnus Damm <damm+renesas@xxxxxxxxxxxxx>
> >
> > Introduce the flag "no_size_align" to allow disabling size-alignment
> > on a per-domain basis. This follows the suggestion by the comment
> > in the code, however a per-device control may be preferred?
> >
> > Needed to make virtual space contiguous for certain devices.
> 
> That sounds very suspicious - a single allocation is contiguous with
> itself by definition, and anyone relying on multiple allocations being
> contiguous with one another is doing it wrong, because there's no way we
> could ever guarantee that (with this allocator, at any rate). I'd be
> very reticent to touch this without a specific example of what problem
> it solves.

Thank you for the comment! This patch was from my request.
But, I completely misunderstood this "size-alignment" behavior.
And, my concern was already resolved by the following patch at last April:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/iommu?id=809eac54cdd62c67afea1e17080e681dfa33dc09

So, no one needs this patch anymore.

Best regards,
Yoshihiro Shimoda





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