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

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

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 ?

-- 
Regards,
Sudeep