From: Tomasz Jeznach <tjeznach@rivosinc.com>

Now that we have every piece in place we can advertise CAP_HTM to
software, allowing any HPM aware driver to make use of the counters.

HPM is enabled/disabled via the 'hpm-counters' attribute. Default value
is 31, max value is also 31. Setting it to zero will disable HPM
support.

Signed-off-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250224190826.1858473-10-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
 hw/riscv/riscv-iommu.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/hw/riscv/riscv-iommu.c b/hw/riscv/riscv-iommu.c
index cdbb848181..d46beb2d64 100644
--- a/hw/riscv/riscv-iommu.c
+++ b/hw/riscv/riscv-iommu.c
@@ -2357,6 +2357,15 @@ static void riscv_iommu_realize(DeviceState *dev, Error **errp)
                   RISCV_IOMMU_CAP_SV48X4 | RISCV_IOMMU_CAP_SV57X4;
     }
 
+    if (s->hpm_cntrs > 0) {
+        /* Clip number of HPM counters to maximum supported (31). */
+        if (s->hpm_cntrs > RISCV_IOMMU_IOCOUNT_NUM) {
+            s->hpm_cntrs = RISCV_IOMMU_IOCOUNT_NUM;
+        }
+        /* Enable hardware performance monitor interface */
+        s->cap |= RISCV_IOMMU_CAP_HPM;
+    }
+
     /* Out-of-reset translation mode: OFF (DMA disabled) BARE (passthrough) */
     s->ddtp = set_field(0, RISCV_IOMMU_DDTP_MODE, s->enable_off ?
                         RISCV_IOMMU_DDTP_MODE_OFF : RISCV_IOMMU_DDTP_MODE_BARE);
@@ -2404,6 +2413,18 @@ static void riscv_iommu_realize(DeviceState *dev, Error **errp)
             RISCV_IOMMU_TR_REQ_CTL_GO_BUSY);
     }
 
+    /* If HPM registers are enabled. */
+    if (s->cap & RISCV_IOMMU_CAP_HPM) {
+        /* +1 for cycle counter bit. */
+        stl_le_p(&s->regs_ro[RISCV_IOMMU_REG_IOCOUNTINH],
+                 ~((2 << s->hpm_cntrs) - 1));
+        stq_le_p(&s->regs_ro[RISCV_IOMMU_REG_IOHPMCYCLES], 0);
+        memset(&s->regs_ro[RISCV_IOMMU_REG_IOHPMCTR_BASE],
+               0x00, s->hpm_cntrs * 8);
+        memset(&s->regs_ro[RISCV_IOMMU_REG_IOHPMEVT_BASE],
+               0x00, s->hpm_cntrs * 8);
+    }
+
     /* Memory region for downstream access, if specified. */
     if (s->target_mr) {
         s->target_as = g_new0(AddressSpace, 1);
-- 
2.48.1