Re: [PATCH 1/6] iommu/qcom: Use the asid read from device-tree if specified

Will Deacon
2022-05-31T16:19:23Z

On Tue, May 31, 2022 at 09:15:22AM -0700, Rob Clark wrote:
> On Tue, May 31, 2022 at 8:46 AM Will Deacon <will@kernel.org> wrote:
> >
> > On Fri, May 27, 2022 at 11:28:56PM +0200, Konrad Dybcio wrote:
> > > From: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
> > >
> > > As specified in this driver, the context banks are 0x1000 apart.
> > > Problem is that sometimes the context number (our asid) does not
> > > match this logic and we end up using the wrong one: this starts
> > > being a problem in the case that we need to send TZ commands
> > > to do anything on a specific context.
> >
> > I don't understand this. The ASID is a software construct, so it shouldn't
> > matter what we use. If it does matter, then please can you explain why? The
> > fact that the context banks are 0x1000 apart seems unrelated.
>
> I think the connection is that mapping from ctx bank to ASID is 1:1

But in what sense? How is the ASID used beyond a tag in the TLB? The commit
message hints at "TZ commands" being a problem.

I'm not doubting that this is needed to make the thing work, I just don't
understand why.

Will