From mboxrd@z Thu Jan 1 00:00:00 1970 From: ard.biesheuvel@linaro.org (Ard Biesheuvel) Date: Wed, 31 Jan 2018 23:48:22 +0000 Subject: ARM64 SMMU Setup In-Reply-To: <2b9c4adb-9645-0c02-ffb6-9357ff421355@linux.intel.com> References: <2b9c4adb-9645-0c02-ffb6-9357ff421355@linux.intel.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org > On 31 Jan 2018, at 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 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. > This confirms my suspicion. It is up to the secure firmware running in EL3 (or secure EL1) to configure the SMMU itself and the interconnect in a way that allows code running in EL2 or non-secure EL1 to access it (note that EL3 is always secure and EL2 is always non-secure) I don?t know the details of the MMU-500 or the way it is integrated into your platform, so I can?t be of any more help, unfortunately. > >>> 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. > > 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 >>> >>> >>> _______________________________________________ >>> linux-arm-kernel mailing list >>> linux-arm-kernel at lists.infradead.org >>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >