[PATCH 5/5] arm_mpam: detect and enable MPAM-Fb PCC support

[Andre Przywara]

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.
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 at arm.com>
---
 drivers/acpi/arm64/mpam.c      |  2 ++
 drivers/resctrl/mpam_devices.c | 46 +++++++++++++++++++++++++++++++---
 2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/arm64/mpam.c b/drivers/acpi/arm64/mpam.c
index 99c2bdbb3314..edb4d10e8dc3 100644
--- a/drivers/acpi/arm64/mpam.c
+++ b/drivers/acpi/arm64/mpam.c
@@ -341,6 +341,8 @@ 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);
 	}
 
 	acpi_mpam_parse_irqs(pdev, tbl_msc, res, &next_res);
diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 62aa04cb6905..6f0d0959d3a4 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -19,6 +19,7 @@
 #include <linux/irqdesc.h>
 #include <linux/list.h>
 #include <linux/lockdep.h>
+#include <linux/mailbox_client.h>
 #include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/printk.h>
@@ -27,6 +28,9 @@
 #include <linux/types.h>
 #include <linux/workqueue.h>
 
+#include <acpi/pcc.h>
+#include <acpi/acpi_io.h>
+
 #include "mpam_internal.h"
 #include "mpam_fb.h"
 
@@ -1042,7 +1046,8 @@ static u64 mpam_msc_read_mbwu_l(struct mpam_msc *msc)
 
 	mpam_mon_sel_lock_held(msc);
 
-	WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz);
+	if (msc->iface == MPAM_IFACE_MMIO)
+		WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz);
 	WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
 
 	mbwu_l_high2 = __mpam_read_reg(msc, MSMON_MBWU_L + 4);
@@ -2042,10 +2047,15 @@ static void mpam_msc_drv_remove(struct platform_device *pdev)
 	mpam_free_garbage();
 }
 
+static void mpam_pcc_rx_callback(struct mbox_client *cl, void *msg)
+{
+	/* TODO: wake up tasks blocked on this MSC's PCC channel */
+}
+
 static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
 {
 	int err;
-	u32 tmp;
+	u32 pcc_subspace_id;
 	struct mpam_msc *msc;
 	struct resource *msc_res;
 	struct device *dev = &pdev->dev;
@@ -2090,7 +2100,8 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
 	if (err)
 		return ERR_PTR(err);
 
-	if (device_property_read_u32(&pdev->dev, "pcc-channel", &tmp))
+	if (device_property_read_u32(&pdev->dev, "pcc-channel",
+				     &pcc_subspace_id))
 		msc->iface = MPAM_IFACE_MMIO;
 	else
 		msc->iface = MPAM_IFACE_PCC;
@@ -2106,6 +2117,35 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
 		}
 		msc->mapped_hwpage_sz = msc_res->end - msc_res->start;
 		msc->mapped_hwpage = io;
+	} else if (msc->iface == MPAM_IFACE_PCC) {
+		u32 msc_id;
+
+		msc->pcc_cl.dev = &pdev->dev;
+		msc->pcc_cl.rx_callback = mpam_pcc_rx_callback;
+		msc->pcc_cl.tx_block = false;
+		msc->pcc_cl.tx_tout = 1000; /* 1s */
+		msc->pcc_cl.knows_txdone = false;
+
+		if (device_property_read_u32(&pdev->dev, "msc-id", &msc_id)) {
+			pr_err("missing MPAM-Fb MSC identifier\n");
+			return ERR_PTR(-EINVAL);
+		}
+		msc->mpam_fb_msc_id = msc_id;
+
+		msc->pcc_chan = pcc_mbox_request_channel(&msc->pcc_cl,
+							 pcc_subspace_id);
+		if (IS_ERR(msc->pcc_chan)) {
+			pr_err("Failed to request MSC PCC channel\n");
+			return (void *)msc->pcc_chan;
+		}
+
+		if (msc->pcc_chan->shmem_size < MPAM_FB_MAX_MSG_SIZE) {
+			pr_err("MPAM-Fb PCC channel size too small.\n");
+			pcc_mbox_free_channel(msc->pcc_chan);
+			return ERR_PTR(-ENOMEM);
+		}
+
+		mutex_init(&msc->pcc_chan_lock);
 	} else {
 		return ERR_PTR(-EINVAL);
 	}
-- 
2.43.0