Re: [PATCH v2 0/3] iommu: Enable non-strict DMA on QCom SD/MMC

[Rajat Jain]

Hi Rob,

On Mon, Aug 2, 2021 at 5:09 PM Rajat Jain <rajatja@xxxxxxxxxx> wrote:
>
> Hi Robin, Doug,
>
> On Wed, Jul 14, 2021 at 8:14 AM Doug Anderson <dianders@xxxxxxxxxxxx> wrote:
> >
> > Hi,
> >
> > On Tue, Jul 13, 2021 at 11:07 AM Robin Murphy <robin.murphy@xxxxxxx> wrote:
> > >
> > > 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

BTW, is there another mirror to this? I (and another colleague) are
getting the following error when trying to clone it:

rajatja@rajat2:~/rob_iommu$ git clone
https://git.gitlab.arm.com/linux-arm/linux-rm.git
Cloning into 'linux-rm'...
remote: Enumerating objects: 125712, done.
remote: Counting objects: 100% (125712/125712), done.
remote: Compressing objects: 100% (41203/41203), done.
error: RPC failed; curl 18 transfer closed with outstanding read data remaining
error: 804 bytes of body are still expected
fetch-pack: unexpected disconnect while reading sideband packet fatal:
early EOF
fatal: fetch-pack: invalid index-pack output rajatja@rajat2:~/rob_iommu$

We've tried both git and https methods.

>
> I was wondering if you got any closer to testing / sending it out? I
> looked at the patches and am trying to understand, would they also
> make it possible to convert at runtime, an existing "non-strict"
> domain (for a particular device) into a "strict" domain leaving the
> other devices/domains as-is? Please let me know when you think your
> patches are good to be tested, and I'd also be interested in trying
> them out.
>
> >
> > Being able to change this at runtime through sysfs sounds great and it
> > fills all the needs I'm aware of, thanks! In Chrome OS we can just use
> > this with some udev rules and get everything we need.
>
> I still have another (inverse) use case where this does not work:
> We have an Intel chromebook with the default domain type being
> non-strict. There is an LTE modem (an internal PCI device which cannot
> be marked external), which we'd like to be treated as a "Strict" DMA
> domain.
>
> Do I understand it right that using Rob's patches, I could potentially
> switch the domain to "strict" *after* booting (since we don't use
> initramfs), but by that time, the driver might have already attached
> to the modem device (using "non-strict" domain), and thus the damage
> may have already been done? So perhaps we still need a device property
> that the firmware could use to indicate "strictness" for certain
> devices at boot?
>
> Thanks,
> Rajat