hw/riscv/riscv-iommu: add IOCOUNTINH mmio writes

RISCV_IOMMU_REG_IOCOUNTINH is done by riscv_iommu_process_iocntinh_cy(),
which is called during riscv_iommu_mmio_write() callback via a new
riscv_iommu_pricess_hpm_writes() helper.

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: <20250224190826.1858473-7-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

hw/riscv/riscv-iommu-hpm.c

@@ -202,3 +202,63 @@ void riscv_iommu_hpm_timer_cb(void *priv)
         riscv_iommu_notify(s, RISCV_IOMMU_INTR_PM);
     }
 }
+
+static void hpm_setup_timer(RISCVIOMMUState *s, uint64_t value)
+{
+    const uint32_t inhibit = riscv_iommu_reg_get32(
+        s, RISCV_IOMMU_REG_IOCOUNTINH);
+    uint64_t overflow_at, overflow_ns;
+
+    if (get_field(inhibit, RISCV_IOMMU_IOCOUNTINH_CY)) {
+        return;
+    }
+
+    /*
+     * We are using INT64_MAX here instead to UINT64_MAX because cycle counter
+     * has 63-bit precision and INT64_MAX is the maximum it can store.
+     */
+    if (value) {
+        overflow_ns = INT64_MAX - value + 1;
+    } else {
+        overflow_ns = INT64_MAX;
+    }
+
+    overflow_at = (uint64_t)qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + overflow_ns;
+
+    if (overflow_at > INT64_MAX) {
+        s->irq_overflow_left = overflow_at - INT64_MAX;
+        overflow_at = INT64_MAX;
+    }
+
+    timer_mod_anticipate_ns(s->hpm_timer, overflow_at);
+}
+
+/* Updates the internal cycle counter state when iocntinh:CY is changed. */
+void riscv_iommu_process_iocntinh_cy(RISCVIOMMUState *s, bool prev_cy_inh)
+{
+    const uint32_t inhibit = riscv_iommu_reg_get32(
+        s, RISCV_IOMMU_REG_IOCOUNTINH);
+
+    /* We only need to process CY bit toggle. */
+    if (!(inhibit ^ prev_cy_inh)) {
+        return;
+    }
+
+    if (!(inhibit & RISCV_IOMMU_IOCOUNTINH_CY)) {
+        /*
+         * Cycle counter is enabled. Just start the timer again and update
+         * the clock snapshot value to point to the current time to make
+         * sure iohpmcycles read is correct.
+         */
+        s->hpmcycle_prev = get_cycles();
+        hpm_setup_timer(s, s->hpmcycle_val);
+    } else {
+        /*
+         * Cycle counter is disabled. Stop the timer and update the cycle
+         * counter to record the current value which is last programmed
+         * value + the cycles passed so far.
+         */
+        s->hpmcycle_val = s->hpmcycle_val + (get_cycles() - s->hpmcycle_prev);
+        timer_del(s->hpm_timer);
+    }
+}

hw/riscv/riscv-iommu-hpm.h

@@ -26,5 +26,6 @@ uint64_t riscv_iommu_hpmcycle_read(RISCVIOMMUState *s);
 void riscv_iommu_hpm_incr_ctr(RISCVIOMMUState *s, RISCVIOMMUContext *ctx,
                               unsigned event_id);
 void riscv_iommu_hpm_timer_cb(void *priv);
+void riscv_iommu_process_iocntinh_cy(RISCVIOMMUState *s, bool prev_cy_inh);
 
 #endif

hw/riscv/riscv-iommu.c

@@ -2024,6 +2024,27 @@ static void riscv_iommu_update_ipsr(RISCVIOMMUState *s, uint64_t data)
     riscv_iommu_reg_mod32(s, RISCV_IOMMU_REG_IPSR, ipsr_set, ipsr_clr);
 }
 
+static void riscv_iommu_process_hpm_writes(RISCVIOMMUState *s,
+                                           uint32_t regb,
+                                           bool prev_cy_inh)
+{
+    switch (regb) {
+    case RISCV_IOMMU_REG_IOCOUNTINH:
+        riscv_iommu_process_iocntinh_cy(s, prev_cy_inh);
+        break;
+
+    case RISCV_IOMMU_REG_IOHPMCYCLES:
+    case RISCV_IOMMU_REG_IOHPMCYCLES + 4:
+        /* not yet implemented */
+        break;
+
+    case RISCV_IOMMU_REG_IOHPMEVT_BASE ...
+        RISCV_IOMMU_REG_IOHPMEVT(RISCV_IOMMU_IOCOUNT_NUM) + 4:
+        /* not yet implemented */
+        break;
+    }
+}
+
 /*
  * Write the resulting value of 'data' for the reg specified
  * by 'reg_addr', after considering read-only/read-write/write-clear
@@ -2051,6 +2072,7 @@ static MemTxResult riscv_iommu_mmio_write(void *opaque, hwaddr addr,
     uint32_t regb = addr & ~3;
     uint32_t busy = 0;
     uint64_t val = 0;
+    bool cy_inh = false;
 
     if ((addr & (size - 1)) != 0) {
         /* Unsupported MMIO alignment or access size */
@@ -2118,6 +2140,16 @@ static MemTxResult riscv_iommu_mmio_write(void *opaque, hwaddr addr,
         busy = RISCV_IOMMU_TR_REQ_CTL_GO_BUSY;
         break;
 
+    case RISCV_IOMMU_REG_IOCOUNTINH:
+        if (addr != RISCV_IOMMU_REG_IOCOUNTINH) {
+            break;
+        }
+        /* Store previous value of CY bit. */
+        cy_inh = !!(riscv_iommu_reg_get32(s, RISCV_IOMMU_REG_IOCOUNTINH) &
+            RISCV_IOMMU_IOCOUNTINH_CY);
+        break;
+
+
     default:
         break;
     }
@@ -2136,6 +2168,12 @@ static MemTxResult riscv_iommu_mmio_write(void *opaque, hwaddr addr,
         stl_le_p(&s->regs_rw[regb], rw | busy);
     }
 
+    /* Process HPM writes and update any internal state if needed. */
+    if (regb >= RISCV_IOMMU_REG_IOCOUNTOVF &&
+        regb <= (RISCV_IOMMU_REG_IOHPMEVT(RISCV_IOMMU_IOCOUNT_NUM) + 4)) {
+        riscv_iommu_process_hpm_writes(s, regb, cy_inh);
+    }
+
     if (process_fn) {
         process_fn(s);
     }