Re: [PATCH] firmware: arm_scmi: Pass shmem address to SMCCC call

[Paul Murphy]

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