On Tue, Oct 17, 2023 at 05:44:28PM +0100, Marc Zyngier wrote: > On Tue, 17 Oct 2023 15:19:46 +0100, > Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx> wrote: > > > > On Fri, Oct 06, 2023 at 02:59:29PM +0200, Lorenzo Pieralisi wrote: > > > The GIC architecture specification defines a set of registers > > > for redistributors and ITSes that control the sharebility and > > > cacheability attributes of redistributors/ITSes initiator ports > > > on the interconnect (GICR_[V]PROPBASER, GICR_[V]PENDBASER, > > > GITS_BASER<n>). > > > > > > Architecturally the GIC provides a means to drive shareability > > > and cacheability attributes signals and related IWB/OWB/ISH barriers > > > but it is not mandatory for designs to wire up the corresponding > > > interconnect signals that control the cacheability/shareability > > > of transactions. > > > > > > Redistributors and ITSes interconnect ports can be connected to > > > non-coherent interconnects that are not able to manage the > > > shareability/cacheability attributes; this implicitly makes > > > the redistributors and ITSes non-coherent observers. > > > > > > So far, the GIC driver on probe executes a write to "probe" for > > > the redistributors and ITSes registers shareability bitfields > > > by writing a value (ie InnerShareable - the shareability domain the > > > CPUs are in) and check it back to detect whether the value sticks or > > > not; this hinges on a GIC programming model behaviour that predates the > > > current specifications, that just define shareability bits as writeable > > > but do not guarantee that writing certain shareability values > > > enable the expected behaviour for the redistributors/ITSes > > > memory interconnect ports. > > > > > > To enable non-coherent GIC designs on ACPI based systems, parse the MADT > > > GICC/GICR/ITS subtables non-coherent flags to determine whether the > > > respective components are non-coherent observers and force the shareability > > > attributes to be programmed into the redistributors and ITSes registers. > > > > > > An ACPI global function (acpi_get_madt_revision()) is added to retrieve > > > the MADT revision, in that it is essential to check the MADT revision > > > before checking for flags that were added with MADT revision 7 so that > > > if the kernel is booted with ACPI tables (MADT rev < 7) it skips parsing > > > the newly added flags (that should be zeroed reserved values for MADT > > > versions < 7 but they could turn out to be buggy and should be ignored). > > > > > > Signed-off-by: Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx> > > > Cc: Robin Murphy <robin.murphy@xxxxxxx> > > > Cc: Mark Rutland <mark.rutland@xxxxxxx> > > > Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx> > > > Cc: Marc Zyngier <maz@xxxxxxxxxx> > > > --- > > > drivers/acpi/processor_core.c | 21 +++++++++++++++++++++ > > > drivers/irqchip/irq-gic-common.h | 8 ++++++++ > > > drivers/irqchip/irq-gic-v3-its.c | 4 ++++ > > > drivers/irqchip/irq-gic-v3.c | 9 +++++++++ > > > include/linux/acpi.h | 3 +++ > > > 5 files changed, 45 insertions(+) > > > > Hi Marc, > > > > just a quick note to ask if, from an ACPI binding POW > > I guess you mean POV. POW has an entirely different meaning... :-/ > > > this patch and related approach make sense to you. > > > > If so, we can start the process to get the ACPI changes drafted > > in: > > > > https://bugzilla.tianocore.org/show_bug.cgi?id=4557 > > > > and deployed in this patch into the ACPI specs, I can log > > an "ACK" in the tianocoreBZ entry above (we will be able to > > rework the code as much as we want, this is just for the > > bindings). > > I'm OK with the overall shape of it. However, I wonder what the > rationale is for spreading the redistributor property all over the map > (in both GICC and GICR structures), while it could be set once and for > all in the core MADT flags (32 bits, of which only one is in use). > > It is bad enough that there are two ways of getting the GICR regions. > Why can't the properties that apply to all of the be common? I don't think we are allowed to add arch specific flags to the MADT since those, supposedly, are cross-architecture (and the only one defined is quite old, though x86 specific). The reason behind spreading the property is the nature of GICC/GICR subtables themselves - we wanted to apply flags only in subtables relevant to the components in question. We could try to add a global flag to the MADT but I would not be surprised if the ECR would be rejected then for the reason I explained above. Thanks, Lorenzo
