Messages in this thread | | | Date | Wed, 07 Sep 2022 12:17:28 +0100 | From | Marc Zyngier <> | Subject | Re: [RFC PATCH v3 4/7] bus/cdx: add cdx-MSI domain with gic-its domain as parent |
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On Tue, 06 Sep 2022 18:19:06 +0100, Jason Gunthorpe <jgg@nvidia.com> wrote: > > On Tue, Sep 06, 2022 at 07:17:58PM +0530, Nipun Gupta wrote: > > > +static void cdx_msi_write_msg(struct irq_data *irq_data, > > + struct msi_msg *msg) > > +{ > > + /* > > + * Do nothing as CDX devices have these pre-populated > > + * in the hardware itself. > > + */ > > +} > > Huh? > > There is no way it can be pre-populated, the addr/data pair, > especially on ARM, is completely under SW control.
There is nothing in the GIC spec that says that.
> There is some commonly used IOVA base in Linux for the ITS page, but > no HW should hardwire that.
That's not strictly true. It really depends on how this block is integrated, and there is a number of existing blocks that know *in HW* how to signal an LPI.
See, as the canonical example, how the mbigen driver doesn't need to know about the address of GITS_TRANSLATER.
Yes, this messes with translation (the access is downstream of the SMMU) if you relied on it to have some isolation, and it has a "black hole" effect as nobody can have an IOVA that overlaps with the physical address of the GITS_TRANSLATER register.
But is it illegal as per the architecture? No. It's just stupid.
M.
-- Without deviation from the norm, progress is not possible.
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