Re: [PATCH v4 10/10] arm_mpam: detect and enable MPAM-Fb PCC support

[Lorenzo Pieralisi <lpieralisi@kernel.org>]

On Fri, Jul 24, 2026 at 11:18:32AM +0100, Sudeep Holla wrote:
> On Thu, Jul 23, 2026 at 05:54:54PM +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.
> > There can be multiple PCC channels, and each channel can serve multiple
> > MSCs, so we need to keep track of the channel usage, using a list and
> > a refcount.
> > 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      |   6 +-
> >  drivers/resctrl/mpam_devices.c | 127 ++++++++++++++++++++++++++++++++-
> >  2 files changed, 129 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/acpi/arm64/mpam.c b/drivers/acpi/arm64/mpam.c
> > index 84963a20c3e7..ca9b8754ae5f 100644
> > --- a/drivers/acpi/arm64/mpam.c
> > +++ b/drivers/acpi/arm64/mpam.c
> > @@ -220,8 +220,8 @@ static struct platform_device * __init acpi_mpam_parse_msc(struct acpi_mpam_msc_
> >  	struct platform_device *pdev __free(platform_device_put) =
> >  		platform_device_alloc("mpam_msc", tbl_msc->identifier);
> 
> Looks like tbl_msc->identifier is getting stashed as pdev->id...
> 
> 
> >  	int next_res = 0, next_prop = 0, err;
> > -	/* pcc, nrdy, affinity and a sentinel */
> > -	struct property_entry props[4] = { 0 };
> > +	/* pcc, msc-id, nrdy, affinity and a sentinel */
> > +	struct property_entry props[5] = { 0 };
> >  	/* mmio, 2xirq, no sentinel. */
> >  	struct resource res[3] = { 0 };
> >  	struct acpi_device *companion;
> > @@ -256,6 +256,8 @@ 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);
> 
> Why is this needed then as you can fetch it as pdev->id ?

I suppose it is to have properties parity between OF and ACPI without
having to change the driver property parsing path.

Lorenzo