On 22/08/2023 09:48, Henry Wang wrote:
Hi Julien,
On Aug 22, 2023, at 16:18, Julien Grall <jul...@xen.org> wrote:
On 22/08/2023 03:11, Henry Wang wrote:
Hi Julien,
Hi,
On Aug 22, 2023, at 05:34, Julien Grall <jul...@xen.org> wrote:
Hi,
On 14/08/2023 05:25, Henry Wang wrote:
From: Penny Zheng <penny.zh...@arm.com>
SMMU subsystem is only supported in MMU system, so we make it dependent
on CONFIG_HAS_MMU.
"only supported" as in it doesn't work with Xen or the HW is not supporting it?
I think currently there are no hardware combination of MPU + SMMU, but
theoretically I think this is a valid combination since SMMU supports the linear
mapping. So would below reword looks good to you:
“Currently the hardware use case of connecting SMMU to MPU system is rarely
seen, so we make CONFIG_ARM_SMMU and CONFIG_ARM_SMMU_V3
dependent on CONFIG_MMU."
I read this as there might be MPU system with SMMU in development. What you
want to explain is why we can't let the developper to select the SMMU driver on
an MPU system.
From my understanding this is because the drivers are expecting to use the
page-tables and the concept doesn't exist in the MPU system. So the drivers are
not ready for the MPU.
I agree.
Also, I am not entirely convinced that anything in passthrough would properly
work with MPU. At least none of the IOMMU drivers are. So I would consider to
completely disable HAS_PASSTHROUGH.
I agree, do you think adding below addition diff to this patch makes sense to
you?
I think it should be a replacement because none of the IOMMU drivers works for the MPU.
So I would rather prefer if we avoid adding "depends on" on all of them (even
if there are only 3) for now.
I am a bit confused, I read your above explanation to the commit message as you
agree with the idea that making SMMU driver not selectable by MPU system.
No. I would rather prefer if HAS_PASSTHROUGH is completely disabled
because I doubt the IOMMU infrastructure will work without any change
for the MPU.
So it sounds incorrect to enable HAS_PASSTHROUGH until one of you
confirm it works.
Cheers,
--
Julien Grall
