[RFC PATCH 35/38] arm_mpam: Add workaround for T241-MPAM-1

James Morse
2025-12-05T22:01:51Z

From: Shanker Donthineni <sdonthineni@nvidia.com>

The MPAM bandwidth partitioning controls will not be correctly configured,
and hardware will retain default configuration register values, meaning
generally that bandwidth will remain unprovisioned.

To address the issue, follow the below steps after updating the MBW_MIN
and/or MBW_MAX registers.

- Perform 64b reads from all 12 bridge MPAM shadow registers at offsets
(0x360048 + slice*0x10000 + partid*8). These registers are read-only.
- Continue iterating until all 12 shadow register values match in a loop.
pr_warn_once if the values fail to match within the loop count 1000.
- Perform 64b writes with the value 0x0 to the two spare registers at
offsets 0x1b0000 and 0x1c0000.

In the hardware, writes to the MPAMCFG_MBW_MAX MPAMCFG_MBW_MIN registers
are transformed into broadcast writes to the 12 shadow registers. The
final two writes to the spare registers cause a final rank of downstream
micro-architectural MPAM registers to be updated from the shadow copies.
The intervening loop to read the 12 shadow registers helps avoid a race
condition where writes to the spare registers occur before all shadow
registers have been updated.

Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
[ morse: Merged the min/max update into a single
mpam_quirk_post_config_change() helper. Stashed the t241_id in the msc
instead of carrying the physical address around. Test the msc quirk bit
instead of a static key. ]
Signed-off-by: James Morse <james.morse@arm.com>
---
Documentation/arch/arm64/silicon-errata.rst | 2 +
drivers/resctrl/mpam_devices.c | 87 +++++++++++++++++++++
drivers/resctrl/mpam_internal.h | 9 +++
3 files changed, 98 insertions(+)

diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst
index a7ec57060f64..4e86b85fe3d6 100644
--- a/Documentation/arch/arm64/silicon-errata.rst
+++ b/Documentation/arch/arm64/silicon-errata.rst
@@ -246,6 +246,8 @@ stable kernels.
+----------------+-----------------+-----------------+-----------------------------+
| NVIDIA | T241 GICv3/4.x | T241-FABRIC-4 | N/A |
+----------------+-----------------+-----------------+-----------------------------+
+| NVIDIA | T241 MPAM | T241-MPAM-1 | N/A |
++----------------+-----------------+-----------------+-----------------------------+
+----------------+-----------------+-----------------+-----------------------------+
| Freescale/NXP | LS2080A/LS1043A | A-008585 | FSL_ERRATUM_A008585 |
+----------------+-----------------+-----------------+-----------------------------+
diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index f0f6f9b55ad4..f1f03ceade0a 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -29,6 +29,16 @@

#include "mpam_internal.h"

+/* Values for the T241 errata workaround */
+#define T241_CHIPS_MAX 4
+#define T241_CHIP_NSLICES 12
+#define T241_SPARE_REG0_OFF 0x1b0000
+#define T241_SPARE_REG1_OFF 0x1c0000
+#define T241_CHIP_ID(phys) FIELD_GET(GENMASK_ULL(44, 43), phys)
+#define T241_SHADOW_REG_OFF(sidx, pid) (0x360048 + (sidx) * 0x10000 + (pid) * 8)
+#define SMCCC_SOC_ID_T241 0x036b0241
+static void __iomem *t241_scratch_regs[T241_CHIPS_MAX];
+
/*
* mpam_list_lock protects the SRCU lists when writing. Once the
* mpam_enabled key is enabled these lists are read-only,
@@ -630,7 +640,44 @@ static struct mpam_msc_ris *mpam_get_or_create_ris(struct mpam_msc *msc,
return ERR_PTR(-ENOENT);
}

+static void mpam_enable_quirk_nvidia_t241(struct mpam_msc *msc,
+ const struct mpam_quirk *quirk)
+{
+ s32 soc_id = arm_smccc_get_soc_id_version();
+ struct resource *r;
+ phys_addr_t phys;
+
+ /*
+ * A mapping to a device other than the MSC is needed, check
+ * SOC_ID is NVIDIA T241 chip (036b:0241)
+ */
+ if (soc_id < 0 || soc_id != SMCCC_SOC_ID_T241)
+ return;
+
+ r = platform_get_resource(msc->pdev, IORESOURCE_MEM, 0);
+ if (!r)
+ return;
+
+ /* Find the internal registers base addr from the CHIP ID */
+ msc->t241_id = T241_CHIP_ID(r->start);
+ phys = FIELD_PREP(GENMASK_ULL(45, 44), msc->t241_id) | 0x19000000ULL;
+
+ t241_scratch_regs[msc->t241_id] = ioremap(phys, SZ_8M);
+ if (WARN_ON_ONCE(!t241_scratch_regs[msc->t241_id]))
+ return;
+
+ mpam_set_quirk(quirk->workaround, msc);
+ pr_info_once("Enabled workaround for NVIDIA T241 erratum T241-MPAM-1\n");
+}
+
static const struct mpam_quirk mpam_quirks[] = {
+ {
+ /* NVIDIA t241 erratum T241-MPAM-1 */
+ .init = mpam_enable_quirk_nvidia_t241,
+ .iidr = MPAM_IIDR_NVIDIA_T421,
+ .iidr_mask = MPAM_IIDR_MATCH_ONE,
+ .workaround = T241_SCRUB_SHADOW_REGS,
+ },
{ NULL }, /* Sentinel */
};

@@ -1372,6 +1419,44 @@ static void mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
__mpam_write_reg(msc, reg, bm);
}

+static void mpam_apply_t241_erratum(struct mpam_msc_ris *ris, u16 partid)
+{
+ int sidx, i, lcount = 1000;
+ void __iomem *regs;
+ u64 val0, val;
+
+ regs = t241_scratch_regs[ris->vmsc->msc->t241_id];
+
+ for (i = 0; i < lcount; i++) {
+ /* Read the shadow register at index 0 */
+ val0 = readq_relaxed(regs + T241_SHADOW_REG_OFF(0, partid));
+
+ /* Check if all the shadow registers have the same value */
+ for (sidx = 1; sidx < T241_CHIP_NSLICES; sidx++) {
+ val = readq_relaxed(regs +
+ T241_SHADOW_REG_OFF(sidx, partid));
+ if (val != val0)
+ break;
+ }
+ if (sidx == T241_CHIP_NSLICES)
+ break;
+ }
+
+ if (i == lcount)
+ pr_warn_once("t241: inconsistent values in shadow regs");
+
+ /* Write a value zero to spare registers to take effect of MBW conf */
+ writeq_relaxed(0, regs + T241_SPARE_REG0_OFF);
+ writeq_relaxed(0, regs + T241_SPARE_REG1_OFF);
+}
+
+static void mpam_quirk_post_config_change(struct mpam_msc_ris *ris, u16 partid,
+ struct mpam_config *cfg)
+{
+ if (mpam_has_quirk(T241_SCRUB_SHADOW_REGS, ris->vmsc->msc))
+ mpam_apply_t241_erratum(ris, partid);
+}
+
/* Called via IPI. Call while holding an SRCU reference */
static void mpam_reprogram_ris_partid(struct mpam_msc_ris *ris, u16 partid,
struct mpam_config *cfg)
@@ -1455,6 +1540,8 @@ static void mpam_reprogram_ris_partid(struct mpam_msc_ris *ris, u16 partid,
mpam_write_partsel_reg(msc, PRI, pri_val);
}

+ mpam_quirk_post_config_change(ris, partid, cfg);
+
mutex_unlock(&msc->part_sel_lock);
}

diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index de3e5faa12b2..70b78cfd1f5b 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -133,6 +133,9 @@ struct mpam_msc {
void __iomem *mapped_hwpage;
size_t mapped_hwpage_sz;

+ /* Values only used on some platforms for quirks */
+ u32 t241_id;
+
struct mpam_garbage garbage;
};

@@ -219,6 +222,7 @@ struct mpam_props {

/* Workaround bits for msc->quirks */
enum mpam_device_quirks {
+ T241_SCRUB_SHADOW_REGS,
MPAM_QUIRK_LAST,
};

@@ -239,6 +243,11 @@ struct mpam_quirk {
FIELD_PREP_CONST(MPAMF_IIDR_REVISION, 0xf ) | \
FIELD_PREP_CONST(MPAMF_IIDR_IMPLEMENTER, 0xfff)

+#define MPAM_IIDR_NVIDIA_T421 FIELD_PREP_CONST(MPAMF_IIDR_PRODUCTID, 0x241) | \
+ FIELD_PREP_CONST(MPAMF_IIDR_VARIANT, 0 ) | \
+ FIELD_PREP_CONST(MPAMF_IIDR_REVISION, 0 ) | \
+ FIELD_PREP_CONST(MPAMF_IIDR_IMPLEMENTER, 0x36b)
+

/* The values for MSMON_CFG_MBWU_FLT.RWBW */
enum mon_filter_options {
--
2.39.5