Re: [PATCH 0/3] Request direct mapping for modem firmware subdevice

[Sai Prakash Ranjan]

Hi Robin,

On 2020-03-10 22:14, Robin Murphy wrote:
> On 10/03/2020 4:23 pm, Joerg Roedel wrote:
> > On Tue, Mar 10, 2020 at 07:30:50PM +0530, Sibi Sankar wrote:
> > > The accesses are initiated by the firmware
> > > and they access modem reserved regions.
> > > However as explained in ^^ any accesses
> > > outside the region will result in a violation
> > > and is controlled through XPUs (protection units).
> >
> > Okay, this sounds like a case for arm_smmu_get_resv_region(). It 
> > should
> > return an entry for the reserved memory region the firmware needs to
> > access, so that generic iommu can setup this mapping.
> >
> > Note that it should return that entry only for your device, not for 
> > all
> > devices. Maybe there is a property in DT or IORT you can set to
> > transport this information into the arm-smmu driver.
> >
> > This is pretty similar to RMRR mapping on the Intel VT-d IOMMU or
> > Unity-mapped ranges in the AMD-Vi IOMMU.
>
> Yup, a way to describe boot-time memory regions in IORT is in the
> process of being specced out; the first attempt at an equivalent for
> DT is here:
>
> https://lore.kernel.org/linux-iommu/20191209150748.2471814-1-thierry.reding@xxxxxxxxx/
>
> If that's not enough and the SMMU still needs to treat certain Stream
> IDs specially because they may be untranslatable (due to having direct
> access to memory as a side-channel), then that should be handled in
> the SoC-specific corner of the SMMU driver, not delegated to
> individual endpoint drivers.

Are you talking about this one for SoC specific change - 
https://lore.kernel.org/patchwork/patch/1183530/

Thanks,
Sai

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