Re: [PATCH] arm64: tegra: only map accessible sysram

[Stephen Warren]

On 9/29/19 2:08 PM, Mian Yousaf Kaukab wrote:
> Most of the SysRAM is secure and only accessible by TF-A.
> Don't map this inaccessible memory in kernel. Only map pages
> used by bpmp driver.

I don't believe this change is correct. The actual patch doesn't
implement mapping a subset of the RAM (a software issue), but rather it
changes the DT representation of the SYSRAM hardware. The SYSRAM
hardware always does start at 0x30000000, even if a subset of the
address range is dedicated to a specific purpose. If the kernel must map
only part of the RAM, then some additional property should indicate
this. Also, I believe it's incorrect to hard-code into the kernel's DT
the range of addresses used by the secure monitor/OS, since this can
vary depending on what the user actually chooses to install as the
secure monitor/OS. Any indication of such regions should be filled in at
runtime by some boot firmware or the secure monitor/OS itself, or
retrieved using some runtime API rather than DT.