Re: [PATCH 5/5] arm_mpam: detect and enable MPAM-Fb PCC support

[Sudeep Holla <sudeep.holla@kernel.org>]

On Thu, Apr 30, 2026 at 11:20:42AM +0200, Andre Przywara wrote:
> Hi Sudeep,
> 
> thanks for having a look!
> 
> On 4/30/26 10:35, Sudeep Holla wrote:
> > On Wed, Apr 29, 2026 at 04:13:39PM +0200, Andre Przywara wrote:
> > > The Arm MPAM-Fb specification [1] describes a protocol to access MSC
> > > registers through a firmware interface. This requires a shared memory
> > > region to hold the message, and a mailbox to trigger the access.
> > > For ACPI this is wrapped as a PCC channel, described using existing
> > > ACPI abstractions.
> > > 
> > > Add code to parse those PCC table descriptions associated with an MSC,
> > > and store the parsed information in the MSC struct.
> > > This will be used by the MPAM-Fb access wrapper code.
> > > 
> > > [1] https://developer.arm.com/documentation/den0144/latest
> > > 
> > > Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> > > ---
> > >   drivers/acpi/arm64/mpam.c      |  2 ++
> > >   drivers/resctrl/mpam_devices.c | 46 +++++++++++++++++++++++++++++++---
> > >   2 files changed, 45 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/acpi/arm64/mpam.c b/drivers/acpi/arm64/mpam.c
> > > index 99c2bdbb3314..edb4d10e8dc3 100644
> > > --- a/drivers/acpi/arm64/mpam.c
> > > +++ b/drivers/acpi/arm64/mpam.c
> > > @@ -341,6 +341,8 @@ static struct platform_device * __init acpi_mpam_parse_msc(struct acpi_mpam_msc_
> > >   	} else if (iface == MPAM_IFACE_PCC) {
> > >   		props[next_prop++] = PROPERTY_ENTRY_U32("pcc-channel",
> > >   							tbl_msc->base_address);
> > > +		props[next_prop++] = PROPERTY_ENTRY_U32("msc-id",
> > > +							tbl_msc->identifier);
> > 
> > I may be looking at the wrong documents, but neither DEN0065 nor DEN0144 carry
> > any definitions of pcc-channel and msc-id for the device with HID
> > "“ARMHAA5C". Since "pcc-channel" is already merged, I think I am looking at
> > wrong documents, please point me to the right one.
> 
> Please excuse my ignorance, but I was under the assumption that the strings
> used here are just unique identifiers that need to match the property_get
> calls in the MPAM code. Is there any requirement to match those
> property_entry.name fields with the names given in some spec? And those
> strings are kernel-internal only, right? But for DT would match exactly the
> property names?
> 

My bad, I missed to see that these are properties added to the software node
created for ACPI. I assumed the ACPI code is expecting this property in the
namespace device with HID 'ARMHAA5C'. Ignore my comment.

-- 
Regards,
Sudeep