[Bug 201753] AMD-Vi: Unable to write to IOMMU perf counter

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=201753

--- Comment #18 from Paul Menzel (pmenzel+bugzilla.kernel.org@molgen.mpg.de) ---
Even with ten tries in the loop, it still fails with the AMD Ryzen 3 2200G with
Radeon Vega Graphics (family: 0x17, model: 0x11, stepping: 0x0):

    [    0.401152] pci 0000:00:00.2: AMD-Vi: Unable to read/write to IOMMU perf
counter. (retry = 0)

```
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 9126efcbaf2c7..70c00ee5ff354 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -1746,7 +1746,7 @@ static void __init init_iommu_perf_ctr(struct amd_iommu
*iommu)

        /* Check if the performance counters can be written to */
        val = 0xabcd;
-       for (retry = 5; retry; retry--) {
+       for (retry = 10; 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)
@@ -1764,7 +1764,7 @@ static void __init init_iommu_perf_ctr(struct amd_iommu
*iommu)
        if (val != val2)
                goto pc_false;

-       pci_info(pdev, "IOMMU performance counters supported\n");
+       pci_info(pdev, "IOMMU performance counters supported (retry = %i)\n",
retry);

        val = readl(iommu->mmio_base + MMIO_CNTR_CONF_OFFSET);
        iommu->max_banks = (u8) ((val >> 12) & 0x3f);
@@ -1773,7 +1773,7 @@ static void __init init_iommu_perf_ctr(struct amd_iommu
*iommu)
        return;

 pc_false:
-       pci_err(pdev, "Unable to read/write to IOMMU perf counter.\n");
+       pci_err(pdev, "Unable to read/write to IOMMU perf counter. (retry =
%i)\n", retry);
        amd_iommu_pc_present = false;
        return;
 }
```

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