Re: [PATCH v5 08/10] arm_mpam: add MPAM-Fb MSC firmware access support

[Ben Horgan]

Hi Andre,

On 7/29/26 14:41, Andre Przywara wrote:
> The Arm MPAM Firmware-backed (Fb) Profile document[1] describes an
> alternative way of accessing the "Memory System Components" (MSC) in an
> MPAM enabled system.
> 
> Normally the MSCs are MMIO mapped, but in some implementations this
> might not be possible (MSC located outside of the local socket, MSC
> mapped secure-only) or desirable (direct MMIO access too slow or needs
> to be mediated through a control processor). MPAM-fb standardises a
> protocol to abstract MSC accesses, building on the SCMI protocol.
> 
> Add functions that do an MSC read or write access by redirecting the
> request through a firmware interface. For now this done via an ACPI
> PCC shared memory and mailbox combination.
> 
> Since the protocol used is only a small subset of the full SCMI spec,
> and the SCMI protocol has no full ACPI support anyway, open-code the
> (simple) SCMI message generation, for just the fields we need.
> 
> [1] https://developer.arm.com/documentation/den0144/latest
> 
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>

[...]

> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 2b81b6b0bf4e..a2193e7df57c 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -11,6 +11,7 @@
>  #include <linux/io.h>
>  #include <linux/jump_label.h>
>  #include <linux/llist.h>
> +#include <linux/mailbox_client.h>
>  #include <linux/mutex.h>
>  #include <linux/resctrl.h>
>  #include <linux/spinlock.h>
> @@ -57,6 +58,15 @@ struct mpam_garbage {
>  	struct platform_device	*pdev;
>  };
>  
> +struct mpam_pcc_chan {
> +	struct list_head	pcc_chans;
> +	struct mbox_client	pcc_cl;
> +	struct pcc_mbox_chan	*pcc_chan;
> +	struct mutex		pcc_chan_lock; /* only one message at a time */
> +	struct kref		refcount;
> +	int			subspace_id;
> +};
> +
>  struct mpam_msc {
>  	/* member of mpam_all_msc */
>  	struct list_head	all_msc_list;
> @@ -66,6 +76,8 @@ struct mpam_msc {
>  
>  	/* Not modified after mpam_is_enabled() becomes true */
>  	enum mpam_msc_iface	iface;
> +	struct mpam_pcc_chan	*pcc_chan;
> +	int			mpam_fb_msc_id;	/* in its own name space */

This gets removed in patch 10 now. I guess you just edited the wrong patch.

Thanks,

Ben