linux-kernel - [PATCH] arm_mpam: Add workaround for T241-MPAM-6

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Message-ID: <20240816131432.993859-1-sdonthineni@nvidia.com>
Date: Fri, 16 Aug 2024 08:14:32 -0500
From: Shanker Donthineni <sdonthineni@...dia.com>
To: James Morse <james.morse@....com>
CC: Catalin Marinas <catalin.marinas@....com>, Shanker Donthineni
	<sdonthineni@...dia.com>, Rohit Mathew <rohit.mathew@....com>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH] arm_mpam: Add workaround for T241-MPAM-6

The registers MSMON_MBWU_L and MSMON_MBWU return the number of
requests rather than the number of bytes transferred.

Bandwidth resource monitoring is performed at the last level cache,
where each request arrive in 64Byte granularity. The current
implementation returns the number of transactions received at the
last level cache but does not provide the value in bytes. Scaling
by 64 gives an accurate byte count to match the MPAM specification
for the MSMON_MBWU and MSMON_MBWU_L registers. This patch fixes
the issue by reporting the actual number of bytes instead of the
number of transactions from __ris_msmon_read().

Signed-off-by: Shanker Donthineni <sdonthineni@...dia.com>
---
 Documentation/arch/arm64/silicon-errata.rst |  2 ++
 drivers/platform/arm64/mpam/mpam_devices.c  | 17 +++++++++++++++--
 drivers/platform/arm64/mpam/mpam_internal.h |  1 +
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst
index 1959013447ee1..1733875f41cd2 100644
--- a/Documentation/arch/arm64/silicon-errata.rst
+++ b/Documentation/arch/arm64/silicon-errata.rst
@@ -239,6 +239,8 @@ stable kernels.
 +----------------+-----------------+-----------------+-----------------------------+
 | NVIDIA         | T241 MPAM       | T241-MPAM-4     | N/A                         |
 +----------------+-----------------+-----------------+-----------------------------+
+| NVIDIA         | T241 MPAM       | T241-MPAM-6     | N/A                         |
++----------------+-----------------+-----------------+-----------------------------+
 +----------------+-----------------+-----------------+-----------------------------+
 | Freescale/NXP  | LS2080A/LS1043A | A-008585        | FSL_ERRATUM_A008585         |
 +----------------+-----------------+-----------------+-----------------------------+
diff --git a/drivers/platform/arm64/mpam/mpam_devices.c b/drivers/platform/arm64/mpam/mpam_devices.c
index d0b787dc4de12..cedf2c896ef5b 100644
--- a/drivers/platform/arm64/mpam/mpam_devices.c
+++ b/drivers/platform/arm64/mpam/mpam_devices.c
@@ -759,6 +759,12 @@ static const struct mpam_quirk mpam_quirks[] = {
 	.iidr_mask  = IIDR_MATCH_ONE,
 	.workaround = T241_FORCE_MBW_MIN_TO_ONE,
 	},
+	{
+	/* NVIDIA t241 erratum T241-MPAM-6 */
+	.iidr       = IIDR_PROD(0x241) | IIDR_VAR(0) | IIDR_REV(0) | IIDR_IMP(0x36b),
+	.iidr_mask  = IIDR_MATCH_ONE,
+	.workaround = T241_MBW_COUNTER_SCALE_64,
+	},
 	{ NULL }, /* Sentinel */
 };
 
@@ -1262,6 +1268,9 @@ static void __ris_msmon_read(void *arg)
 			now = FIELD_GET(MSMON___VALUE, now);
 		}
 
+		if (mpam_has_quirk(T241_MBW_COUNTER_SCALE_64, msc))
+			now *= 64;
+
 		if (nrdy)
 			break;
 
@@ -1269,8 +1278,12 @@ static void __ris_msmon_read(void *arg)
 			break;
 
 		/* Add any pre-overflow value to the mbwu_state->val */
-		if (mbwu_state->prev_val > now)
-			overflow_val = mpam_msmon_overflow_val(ris) - mbwu_state->prev_val;
+		if (mbwu_state->prev_val > now) {
+			overflow_val = mpam_msmon_overflow_val(ris);
+			if (mpam_has_quirk(T241_MBW_COUNTER_SCALE_64, msc))
+				overflow_val *= 64;
+			overflow_val -= mbwu_state->prev_val;
+		}
 
 		mbwu_state->prev_val = now;
 		mbwu_state->correction += overflow_val;
diff --git a/drivers/platform/arm64/mpam/mpam_internal.h b/drivers/platform/arm64/mpam/mpam_internal.h
index 6e43acabdcaa2..266d8a4e91905 100644
--- a/drivers/platform/arm64/mpam/mpam_internal.h
+++ b/drivers/platform/arm64/mpam/mpam_internal.h
@@ -237,6 +237,7 @@ static inline void mpam_clear_feature(enum mpam_device_features feat,
 enum mpam_device_quirks {
 	T241_SCRUB_SHADOW_REGS,
 	T241_FORCE_MBW_MIN_TO_ONE,
+	T241_MBW_COUNTER_SCALE_64,
 	MPAM_QUIRK_LAST,
 };
 
-- 
2.25.1