[PATCH v6 10/10] 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.
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@xxxxxxx>
Tested-by: Ritwick Sharma <ritwick.sharma@xxxxxxx>
---
 drivers/resctrl/mpam_devices.c  | 111 +++++++++++++++++++++++++++++++-
 drivers/resctrl/mpam_fb.c       |  41 ++++++++++++
 drivers/resctrl/mpam_internal.h |   2 +
 3 files changed, 152 insertions(+), 2 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 606ae4af2be9..8490034c7db9 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -19,14 +19,19 @@
 #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>
+#include <linux/property.h>
 #include <linux/srcu.h>
 #include <linux/spinlock.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
 
+#include <acpi/pcc.h>
+#include <acpi/acpi_io.h>
+
 #include "mpam_internal.h"
 
 /* Values for the T241 errata workaround */
@@ -49,6 +54,84 @@ static LIST_HEAD(mpam_all_msc);
 
 struct srcu_struct mpam_srcu;
 
+/* PCC channels might be serving multiple MSCs, so keep a refcounted list. */
+static DEFINE_MUTEX(pcc_chan_list_lock);
+static LIST_HEAD(pcc_chan_list);
+
+static void mpam_pcc_chan_release(struct kref *ref)
+{
+	struct mpam_pcc_chan *cur = container_of(ref, struct mpam_pcc_chan,
+						 refcount);
+
+	pcc_mbox_free_channel(cur->pcc_chan);
+	list_del(&cur->pcc_chans);
+	mutex_destroy(&cur->pcc_chan_lock);
+	kfree(cur);
+}
+
+static struct mpam_pcc_chan *mpam_pcc_chan_get(struct device *dev,
+					       int subspace_id)
+{
+	struct mpam_pcc_chan *cur;
+
+	guard(mutex)(&pcc_chan_list_lock);
+
+	list_for_each_entry(cur, &pcc_chan_list, pcc_chans) {
+		if (cur->subspace_id == subspace_id) {
+			kref_get(&cur->refcount);
+
+			return cur;
+		}
+	}
+
+	cur = kzalloc_obj(*cur);
+	if (!cur)
+		return ERR_PTR(-ENOMEM);
+
+	cur->pcc_cl.dev = dev;
+	cur->pcc_cl.tx_block = true;
+
+	cur->pcc_chan = pcc_mbox_request_channel(&cur->pcc_cl, subspace_id);
+	if (IS_ERR(cur->pcc_chan)) {
+		long err = PTR_ERR(cur->pcc_chan);
+
+		kfree(cur);
+		return ERR_PTR(err);
+	}
+
+	/* Timeout based on the "nominal latency" from the PCC ACPI table. */
+	cur->pcc_cl.tx_tout = cur->pcc_chan->latency * 5;
+
+	mutex_init(&cur->pcc_chan_lock);
+
+	cur->subspace_id = subspace_id;
+	kref_init(&cur->refcount);
+
+	list_add_tail(&cur->pcc_chans, &pcc_chan_list);
+
+	return cur;
+}
+
+static int mpam_pcc_chan_put(struct mpam_pcc_chan *pcc_chan)
+{
+	struct mpam_pcc_chan *cur, *tmp;
+
+	if (!pcc_chan)
+		return 0;
+
+	guard(mutex)(&pcc_chan_list_lock);
+
+	list_for_each_entry_safe(cur, tmp, &pcc_chan_list, pcc_chans) {
+		if (cur == pcc_chan) {
+			kref_put(&cur->refcount, mpam_pcc_chan_release);
+
+			return 0;
+		}
+	}
+
+	return -ENOENT;
+}
+
 /*
  * Number of MSCs that have been probed. Once all MSCs have been probed MPAM
  * can be enabled.
@@ -2222,6 +2305,8 @@ static void mpam_msc_drv_remove(struct platform_device *pdev)
 {
 	struct mpam_msc *msc = platform_get_drvdata(pdev);
 
+	mpam_pcc_chan_put(msc->pcc_chan);
+
 	mutex_lock(&mpam_list_lock);
 	mpam_msc_destroy(msc);
 	mutex_unlock(&mpam_list_lock);
@@ -2232,7 +2317,7 @@ static void mpam_msc_drv_remove(struct platform_device *pdev)
 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;
@@ -2280,7 +2365,7 @@ 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(dev, "pcc-channel", &pcc_subspace_id))
 		msc->iface = MPAM_IFACE_MMIO;
 	else
 		msc->iface = MPAM_IFACE_PCC;
@@ -2296,6 +2381,28 @@ 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) {
+		int ret;
+
+		msc->pcc_chan = mpam_pcc_chan_get(dev, pcc_subspace_id);
+		if (IS_ERR(msc->pcc_chan)) {
+			pr_err("Failed to request MSC PCC channel\n");
+			return ERR_CAST(msc->pcc_chan);
+		}
+
+		ret = mpam_fb_check_shared_buffer_size(msc);
+		if (ret) {
+			mpam_pcc_chan_put(msc->pcc_chan);
+
+			return ERR_PTR(ret);
+		}
+
+		ret = mpam_fb_check_protocol_version(msc);
+		if (ret) {
+			mpam_pcc_chan_put(msc->pcc_chan);
+
+			return ERR_PTR(ret);
+		}
 	} else {
 		return ERR_PTR(-EINVAL);
 	}
diff --git a/drivers/resctrl/mpam_fb.c b/drivers/resctrl/mpam_fb.c
index e2ce28a602aa..2014aa032677 100644
--- a/drivers/resctrl/mpam_fb.c
+++ b/drivers/resctrl/mpam_fb.c
@@ -37,6 +37,11 @@
 #define MPAM_MSC_TOKEN_MASK		GENMASK(27, 18)
 
 #define MPAM_FB_PROT_HEADER_LEN		sizeof(u32)
+/* The longest message is MPAM_MSC_WRITE, with 4 parameters. */
+#define MPAM_FB_MAX_MSG_SIZE		(4 * sizeof(u32))
+
+#define MPAM_FB_VERSION_MAJOR_MASK	GENMASK(31, 16)
+#define MPAM_FB_VERSION_MINOR_MASK	GENMASK(15, 0)
 
 static atomic_t mpam_fb_token = ATOMIC_INIT(0);
 
@@ -209,3 +214,39 @@ int mpam_fb_send_write_request(struct mpam_msc *msc, u16 reg, u32 value)
 	return mpam_fb_send_request(msc->pcc_chan, msc->id, reg, &value,
 				    MPAM_MSC_WRITE_CMD);
 }
+
+/* We only support MPAM-Fb protocol version 1.x */
+int mpam_fb_check_protocol_version(struct mpam_msc *msc)
+{
+	u32 version;
+	int ret;
+
+	ret = mpam_fb_send_request(msc->pcc_chan, 0,
+				   0, &version, MPAM_PROTOCOL_VERSION_CMD);
+	if (ret)
+		return ret;
+
+	if (FIELD_GET(MPAM_FB_VERSION_MAJOR_MASK, version) != 1) {
+		pr_err("Incompatible MPAM-Fb protocol version %ld.%ld\n",
+		       FIELD_GET(MPAM_FB_VERSION_MAJOR_MASK, version),
+		       FIELD_GET(MPAM_FB_VERSION_MINOR_MASK, version));
+
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+int mpam_fb_check_shared_buffer_size(struct mpam_msc *msc)
+{
+	int min_buffer_size = MPAM_FB_MAX_MSG_SIZE +
+			      sizeof(struct acpi_pcct_ext_pcc_shared_memory);
+
+	if (msc->pcc_chan->pcc_chan->shmem_size < min_buffer_size) {
+		pr_err("MPAM-Fb PCC channel size too small.\n");
+
+		return -ENOMEM;
+	}
+
+	return 0;
+}
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index f13a79a84c58..8859189088f3 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -528,6 +528,8 @@ static inline void mpam_resctrl_teardown_class(struct mpam_class *class) { }
 /* MPAM-Fb Firmware-backed protocol wrappers */
 int mpam_fb_send_read_request(struct mpam_msc *msc, u16 reg, u32 *result);
 int mpam_fb_send_write_request(struct mpam_msc *msc, u16 reg, u32 value);
+int mpam_fb_check_protocol_version(struct mpam_msc *msc);
+int mpam_fb_check_shared_buffer_size(struct mpam_msc *msc);
 
 /*
  * MPAM MSCs have the following register layout. See:
-- 
2.43.0