On 31/01/18 23:31, Thor Thayer wrote:
Hi Ard,
On 01/31/2018 04:21 PM, Ard Biesheuvel wrote:
On 31 January 2018 at 22:09, Thor Thayer <[email protected]>
wrote:
Hi,
I'm enabling the ARM SMMU-500 on an ARM64 A53. I'm hitting a data
abort in
the probe functions because I'm accessing the registers in EL1 mode.
Why do you think the fact that you are running at EL1 is causing the
data abort?
Yes, I may not be diagnosing this correctly. I narrowed it down to
failing on the first read in arm_smmu_device_cfg_probe().
When I read the same register with a debugger (I'm in EL1), it fails. I
just realized the read also fails in EL2.
If I elevate the read to EL3, I can read the default reset value from
the register but I mistakenly thought this was EL2.
Yes, this sounds like a TrustZone controller preventing non-secure
access to the SMMU altogether. Even if you try to access MMU-500's
secure-only registers from non-secure, "successful" accesses to those
should behave as RAZ/WI rather than aborting.
Linux starts in EL2 mode but drops down to EL1 mode by the time it
reaches
the arm-smmu probe function.
Is there something else I need to add to either move the arm-smmu probe
earlier or remain in EL2 until after the arm-smmu probe?
No. I am pretty sure EL2 vs EL1 is not causing your issue. Could you
elaborate on the nature of the exception you are getting?
The error I'm getting is:
Unhandled fault: synchronous external abort (0x96000010) at
0xffff000008e40020
Internal error: : 96000010 [#1] PREEMPT SMP
To be honest I got lost trying to decode 0x96000010 and I may have used
the wrong ARM document. I ended up interpreting this as Data Abort taken
without an Exception level from the ARMv8 ARM.
Additionally, the SMMU documentation seemed to indicate the Hypervisor
would need to run at EL2 so I ran with that.
Beware that much of the SMMU documentation is based on some theoretical
idea of how software might work, and bears little or no relation to what
real software actually does ;)
Robin.
Thank you for the reply and I'll go back and examine my assumptions again.
Thor
A Google search didn't turn up anything so I hoped posting to the
list would
help.
Thanks in advance,
Thor
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