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

[Andre Przywara]

Hi Ben,

thanks for having a look!

On 7/29/26 16:51, Ben Horgan wrote:
> 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.

Argh, you are right, I squashed the fix into 10/10, but indeed the 
member is already introduced here.
Good catch!

Cheers,
Andre