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

[Sibi Sankar]

Hey Joerg,
Thanks for taking time to review
the series!

On 2020-03-10 16:53, Joerg Roedel wrote:
> On Mon, Mar 09, 2020 at 11:52:52PM +0530, Sibi Sankar wrote:
> > The Q6 modem sub-system has direct access to DDR through memnoc and
> > an indirect access routed through a SMMU which MSS CE (crypto engine
> > sub-component of MSS) uses during out of reset sequence. Request 
> > direct
> > mapping for the modem-firmware subdevice since smmu is not expected
> > to provide access control/translation for these SIDs (sandboxing of 
> > the
> > modem is achieved through XPUs engaged using SMC calls).
>
> So the DMA accesses are initiated by the firmware and need to be direct
> mapped? Which memory region do they access?

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).

With ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT y
the firmware SIDs will explicitly need to
be directly mapped to avoid observing
global faults in the absence of secure
firmware (TrustZone) programming the modem
SIDs as S2CR-Bypass.

> Regards,
>
> 	Joerg

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