Re: [PATCH 10/33] arm_mpam: Add probe/remove for mpam msc driver and kbuild boiler plate

Hi Ben,

On 01/09/2025 10:11, Ben Horgan wrote:

On 8/22/25 16:29, James Morse wrote:

quoted

Probing MPAM is convoluted. MSCs that are integrated with a CPU may
only be accessible from those CPUs, and they may not be online.
Touching the hardware early is pointless as MPAM can't be used until
the system-wide common values for num_partid and num_pmg have been
discovered.

Start with driver probe/remove and mapping the MSC.

quoted

diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
new file mode 100644
index 000000000000..07e0f240eaca
--- /dev/null
+++ b/drivers/resctrl/mpam_internal.h

@@ -0,0 +1,62 @@

quoted

+struct mpam_msc {
+	/* member of mpam_all_msc */
+	struct list_head        glbl_list;
+
+	int			id;
+	struct platform_device *pdev;
+
+	/* Not modified after mpam_is_enabled() becomes true */
+	enum mpam_msc_iface	iface;
+	u32			pcc_subspace_id;
+	struct mbox_client	pcc_cl;
+	struct pcc_mbox_chan	*pcc_chan;
+	u32			nrdy_usec;
+	cpumask_t		accessibility;
+
+	/*
+	 * probe_lock is only take during discovery. After discovery these
+	 * properties become read-only and the lists are protected by SRCU.
+	 */
+	struct mutex		probe_lock;
+	unsigned long		ris_idxs[128 / BITS_PER_LONG];

Why is this sized this way? RIS_MAX is 4 bits and so there are at most
16 RIS per msc.

Hmmm, lost in time - I agree with the 16 reasoning. Fixed.
(It's likely due to RES0 space above the field - but that has been filled in with other
 stuff since then. RIS was added as a 'backward compatible feature' - I was wary of them
 extending it)

quoted

+	u32			ris_max;
+
+	/* mpam_msc_ris of this component */
+	struct list_head	ris;
+
+	/*
+	 * part_sel_lock protects access to the MSC hardware registers that are
+	 * affected by MPAMCFG_PART_SEL. (including the ID registers that vary
+	 * by RIS).
+	 * If needed, take msc->lock first.
+	 */
+	struct mutex		part_sel_lock;
+
+	/*
+	 * mon_sel_lock protects access to the MSC hardware registers that are
+	 * affeted by MPAMCFG_MON_SEL.
+	 * If needed, take msc->lock first.
+	 */
+	struct mutex		outer_mon_sel_lock;
+	raw_spinlock_t		inner_mon_sel_lock;
+	unsigned long		inner_mon_sel_flags;
+
+	void __iomem		*mapped_hwpage;
+	size_t			mapped_hwpage_sz;
+};
+
+#endif /* MPAM_INTERNAL_H */

Thanks,

James