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Subject[PATCH AUTOSEL 5.10 21/47] iommu/amd: Fix performance counter initialization
Date
From: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>

[ Upstream commit 6778ff5b21bd8e78c8bd547fd66437cf2657fd9b ]

Certain AMD platforms enable power gating feature for IOMMU PMC,
which prevents the IOMMU driver from updating the counter while
trying to validate the PMC functionality in the init_iommu_perf_ctr().
This results in disabling PMC support and the following error message:

"AMD-Vi: Unable to read/write to IOMMU perf counter"

To workaround this issue, disable power gating temporarily by programming
the counter source to non-zero value while validating the counter,
and restore the prior state afterward.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Tested-by: Tj (Elloe Linux) <ml.linux@elloe.vision>
Link: https://lore.kernel.org/r/20210208122712.5048-1-suravee.suthikulpanit@amd.com
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201753
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/iommu/amd/init.c | 45 ++++++++++++++++++++++++++++++----------
1 file changed, 34 insertions(+), 11 deletions(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index c842545368fd..3c215f0a6052 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -12,6 +12,7 @@
#include <linux/acpi.h>
#include <linux/list.h>
#include <linux/bitmap.h>
+#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/syscore_ops.h>
#include <linux/interrupt.h>
@@ -254,6 +255,8 @@ static enum iommu_init_state init_state = IOMMU_START_STATE;
static int amd_iommu_enable_interrupts(void);
static int __init iommu_go_to_state(enum iommu_init_state state);
static void init_device_table_dma(void);
+static int iommu_pc_get_set_reg(struct amd_iommu *iommu, u8 bank, u8 cntr,
+ u8 fxn, u64 *value, bool is_write);

static bool amd_iommu_pre_enabled = true;

@@ -1717,13 +1720,11 @@ static int __init init_iommu_all(struct acpi_table_header *table)
return 0;
}

-static int iommu_pc_get_set_reg(struct amd_iommu *iommu, u8 bank, u8 cntr,
- u8 fxn, u64 *value, bool is_write);
-
-static void init_iommu_perf_ctr(struct amd_iommu *iommu)
+static void __init init_iommu_perf_ctr(struct amd_iommu *iommu)
{
+ int retry;
struct pci_dev *pdev = iommu->dev;
- u64 val = 0xabcd, val2 = 0, save_reg = 0;
+ u64 val = 0xabcd, val2 = 0, save_reg, save_src;

if (!iommu_feature(iommu, FEATURE_PC))
return;
@@ -1731,17 +1732,39 @@ static void init_iommu_perf_ctr(struct amd_iommu *iommu)
amd_iommu_pc_present = true;

/* save the value to restore, if writable */
- if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, false))
+ if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, false) ||
+ iommu_pc_get_set_reg(iommu, 0, 0, 8, &save_src, false))
goto pc_false;

- /* Check if the performance counters can be written to */
- if ((iommu_pc_get_set_reg(iommu, 0, 0, 0, &val, true)) ||
- (iommu_pc_get_set_reg(iommu, 0, 0, 0, &val2, false)) ||
- (val != val2))
+ /*
+ * Disable power gating by programing the performance counter
+ * source to 20 (i.e. counts the reads and writes from/to IOMMU
+ * Reserved Register [MMIO Offset 1FF8h] that are ignored.),
+ * which never get incremented during this init phase.
+ * (Note: The event is also deprecated.)
+ */
+ val = 20;
+ if (iommu_pc_get_set_reg(iommu, 0, 0, 8, &val, true))
goto pc_false;

+ /* Check if the performance counters can be written to */
+ val = 0xabcd;
+ for (retry = 5; retry; retry--) {
+ if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &val, true) ||
+ iommu_pc_get_set_reg(iommu, 0, 0, 0, &val2, false) ||
+ val2)
+ break;
+
+ /* Wait about 20 msec for power gating to disable and retry. */
+ msleep(20);
+ }
+
/* restore */
- if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, true))
+ if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, true) ||
+ iommu_pc_get_set_reg(iommu, 0, 0, 8, &save_src, true))
+ goto pc_false;
+
+ if (val != val2)
goto pc_false;

pci_info(pdev, "IOMMU performance counters supported\n");
--
2.30.1
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