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Subject: Re: [PATCH v2 0/3] iommu: Enable non-strict DMA on QCom SD/MMC
To:     Doug Anderson <dianders@chromium.org>,
        Joerg Roedel <joro@8bytes.org>
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From:   Robin Murphy <robin.murphy@arm.com>
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Date:   Tue, 13 Jul 2021 19:07:00 +0100
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On 2021-07-08 15:36, Doug Anderson wrote:
[...]
>> Or document for the users that want performance how to
>> change the setting, so that they can decide.
> 
> Pushing this to the users can make sense for a Linux distribution but
> probably less sense for an embedded platform. So I'm happy to make
> some way for a user to override this (like via kernel command line),
> but I also strongly believe there should be a default that users don't
> have to futz with that we think is correct.

FYI I did make progress on the "punt it to userspace" approach. I'm not 
posting it even as an RFC yet because I still need to set up a machine 
to try actually testing any of it (it's almost certainly broken 
somewhere), but in the end it comes out looking surprisingly not too bad 
overall. If you're curious to take a look in the meantime I put it here:

https://gitlab.arm.com/linux-arm/linux-rm/-/commits/iommu/fq

Cheers,
Robin.