hw/riscv/riscv-iommu: add riscv-iommu-hpm file

The HPM (Hardware Performance Monitor) support consists of almost 7
hundred lines that would be put on top of the base riscv-iommu
emulation.

To avoid clogging riscv-iommu.c, add a separated riscv-iommu-hpm file
that will contain HPM specific code.

We'll start by adding riscv_iommu_hpmcycle_read(), a helper that will be
called during the riscv_iommu_mmio_read() callback.

This change will have no effect on the existing emulation since we're
not declaring HPM feature 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: <20250224190826.1858473-4-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

hw/riscv/meson.build

@@ -10,7 +10,8 @@ riscv_ss.add(when: 'CONFIG_SIFIVE_U', if_true: files('sifive_u.c'))
 riscv_ss.add(when: 'CONFIG_SPIKE', if_true: files('spike.c'))
 riscv_ss.add(when: 'CONFIG_MICROCHIP_PFSOC', if_true: files('microchip_pfsoc.c'))
 riscv_ss.add(when: 'CONFIG_ACPI', if_true: files('virt-acpi-build.c'))
-riscv_ss.add(when: 'CONFIG_RISCV_IOMMU', if_true: files('riscv-iommu.c', 'riscv-iommu-pci.c', 'riscv-iommu-sys.c'))
+riscv_ss.add(when: 'CONFIG_RISCV_IOMMU', if_true: files(
+	'riscv-iommu.c', 'riscv-iommu-pci.c', 'riscv-iommu-sys.c', 'riscv-iommu-hpm.c'))
 riscv_ss.add(when: 'CONFIG_MICROBLAZE_V', if_true: files('microblaze-v-generic.c'))
 
 hw_arch += {'riscv': riscv_ss}

hw/riscv/riscv-iommu-hpm.c

@@ -0,0 +1,54 @@
+/*
+ * RISC-V IOMMU - Hardware Performance Monitor (HPM) helpers
+ *
+ * Copyright (C) 2022-2023 Rivos Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2 or later, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/timer.h"
+#include "cpu_bits.h"
+#include "riscv-iommu-hpm.h"
+#include "riscv-iommu.h"
+#include "riscv-iommu-bits.h"
+#include "trace.h"
+
+/* For now we assume IOMMU HPM frequency to be 1GHz so 1-cycle is of 1-ns. */
+static inline uint64_t get_cycles(void)
+{
+    return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+}
+
+uint64_t riscv_iommu_hpmcycle_read(RISCVIOMMUState *s)
+{
+    const uint64_t cycle = riscv_iommu_reg_get64(
+        s, RISCV_IOMMU_REG_IOHPMCYCLES);
+    const uint32_t inhibit = riscv_iommu_reg_get32(
+        s, RISCV_IOMMU_REG_IOCOUNTINH);
+    const uint64_t ctr_prev = s->hpmcycle_prev;
+    const uint64_t ctr_val = s->hpmcycle_val;
+
+    if (get_field(inhibit, RISCV_IOMMU_IOCOUNTINH_CY)) {
+        /*
+         * Counter should not increment if inhibit bit is set. We can't really
+         * stop the QEMU_CLOCK_VIRTUAL, so we just return the last updated
+         * counter value to indicate that counter was not incremented.
+         */
+        return (ctr_val & RISCV_IOMMU_IOHPMCYCLES_COUNTER) |
+               (cycle & RISCV_IOMMU_IOHPMCYCLES_OVF);
+    }
+
+    return (ctr_val + get_cycles() - ctr_prev) |
+        (cycle & RISCV_IOMMU_IOHPMCYCLES_OVF);
+}

hw/riscv/riscv-iommu-hpm.h

@@ -0,0 +1,27 @@
+/*
+ * RISC-V IOMMU - Hardware Performance Monitor (HPM) helpers
+ *
+ * Copyright (C) 2022-2023 Rivos Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2 or later, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef HW_RISCV_IOMMU_HPM_H
+#define HW_RISCV_IOMMU_HPM_H
+
+#include "qom/object.h"
+#include "hw/riscv/riscv-iommu.h"
+
+uint64_t riscv_iommu_hpmcycle_read(RISCVIOMMUState *s);
+
+#endif

hw/riscv/riscv-iommu.c

@@ -29,6 +29,7 @@
 #include "cpu_bits.h"
 #include "riscv-iommu.h"
 #include "riscv-iommu-bits.h"
+#include "riscv-iommu-hpm.h"
 #include "trace.h"
 
 #define LIMIT_CACHE_CTX               (1U << 7)
@@ -2153,7 +2154,28 @@ static MemTxResult riscv_iommu_mmio_read(void *opaque, hwaddr addr,
         return MEMTX_ACCESS_ERROR;
     }
 
-    ptr = &s->regs_rw[addr];
+    /* Compute cycle register value. */
+    if ((addr & ~7) == RISCV_IOMMU_REG_IOHPMCYCLES) {
+        val = riscv_iommu_hpmcycle_read(s);
+        ptr = (uint8_t *)&val + (addr & 7);
+    } else if ((addr & ~3) == RISCV_IOMMU_REG_IOCOUNTOVF) {
+        /*
+         * Software can read RISCV_IOMMU_REG_IOCOUNTOVF before timer
+         * callback completes. In which case CY_OF bit in
+         * RISCV_IOMMU_IOHPMCYCLES_OVF would be 0. Here we take the
+         * CY_OF bit state from RISCV_IOMMU_REG_IOHPMCYCLES register as
+         * it's not dependent over the timer callback and is computed
+         * from cycle overflow.
+         */
+        val = ldq_le_p(&s->regs_rw[addr]);
+        val |= (riscv_iommu_hpmcycle_read(s) & RISCV_IOMMU_IOHPMCYCLES_OVF)
+                   ? RISCV_IOMMU_IOCOUNTOVF_CY
+                   : 0;
+        ptr = (uint8_t *)&val + (addr & 3);
+    } else {
+        ptr = &s->regs_rw[addr];
+    }
+
     val = ldn_le_p(ptr, size);
 
     *data = val;

hw/riscv/riscv-iommu.h

@@ -81,6 +81,10 @@ struct RISCVIOMMUState {
 
     QLIST_ENTRY(RISCVIOMMUState) iommus;
     QLIST_HEAD(, RISCVIOMMUSpace) spaces;
+
+    /* HPM cycle counter */
+    uint64_t hpmcycle_val;      /* Current value of cycle register */
+    uint64_t hpmcycle_prev;     /* Saved value of QEMU_CLOCK_VIRTUAL clock */
 };
 
 void riscv_iommu_pci_setup_iommu(RISCVIOMMUState *iommu, PCIBus *bus,