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.
Tested-by: Tj (Elloe Linux)
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201753
Signed-off-by: Suravee Suthikulpanit
---
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 83d8ab2aed9f..01da76dc1caa 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -12,6 +12,7 @@
#include
#include
#include
+#include
#include
#include
#include
@@ -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;
@@ -1712,13 +1715,11 @@ 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;
@@ -1726,17 +1727,39 @@ 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, _reg, false))
+ if (iommu_pc_get_set_reg(iommu, 0, 0, 0, _reg, false) ||
+ iommu_pc_get_set_reg(iommu, 0, 0, 8, _src, false))
goto pc_false;
- /* Check if the performance counters can be written to */
- if ((iommu_pc_get_set_reg(iommu, 0, 0, 0, , true)) ||
- (iommu_pc_get_set_reg(iommu, 0, 0, 0, , 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, , 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, , true) ||
+ iommu_pc_get_set_reg(iommu, 0, 0, 0, , 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, _reg, true))
+ if (iommu_pc_get_set_reg(iommu, 0, 0, 0, _reg, true) ||
+ iommu_pc_get_set_reg(iommu, 0, 0, 8, _src, true))
+ goto pc_false;
+
+ if (val != val2)
goto pc_false;
pci_info(pdev, "IOMMU performance counters supported\n");
--
2.17.1
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