Messages in this thread | | | Date | Tue, 10 Mar 2020 19:30:50 +0530 | From | Sibi Sankar <> | Subject | Re: [PATCH 0/3] Request direct mapping for modem firmware subdevice |
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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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