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

[Sibi Sankar]

Hey Christoph,
Thanks for taking time to review
the series.

On 2020-03-16 21:20, Christoph Hellwig 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).
>
> Please fix your device tree so that the device isn't bound to an
> IOMMU.

the bindings proposed in the series
would add a sub-device with an iommu
property.

modem_pil: remoteproc@xxxxx {
...
   modem-firmware {
        iommus = <&apps_smmu 0x460 0x1>;
   };
...
};

Remoteproc device will not have a iommu
property but modem-firmware sub-device
will.

With ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT y,
we would want to configure the SID either
in direct mapping or bypass (either will
do since protection is achieved through
other means)

https://lore.kernel.org/lkml/497e40b8-300f-1b83-4312-93a58c459d1d@xxxxxxx/

Currently the restructuring is trending
towards whats discussed in the ^^ thread.
i.e either direct mapping/bypass will be
done in the SoC specific corner of the
SMMU driver.

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