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SubjectRe: [PATCH] firmware: arm_scmi: Pass shmem address to SMCCC call
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Hi Florian


On 7/16/20 20:57, Florian Fainelli wrote:

>>>
>>> Given that the kernel must somehow reserve this memory as a shared
>>> memory area for obvious reasons, and the trusted firmware must also
>>> ensure it treats this memory region with specific permissions in its
>>> translation regime, does it really make sense to give that much
>>> flexibility?
>>
>> Well, the trusted firmware might reserve a bigger region to be used for
>> other service as well. In other words, the MMU of TF-A is not necessary
>> specifically set up for this region, but, possibly, for a bigger
>> general shared region.
>
> But presumably the Linux shared memory area should be mapped in a
> slightly different way than
>


Sorry - could you clarify what you mean by that?

Just checking if we are doing everything correctly.

I didn't understand that there is a connection between the TF-A MMU
tables for this region and the normal world MMU tables?

For example:

TF-A may map physical address range: 0x0 -> 0x400_000 as 'normal' memory
for various purposes.

Linux SCMI driver could map physical address range, eg: 0x300_000 ->
0x301_000 as IO memory for mailbox purpose only.

Is there any issue here?

Regards,

Paul

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