Re: [PATCH v4 11/11] hw/riscv: virt: Add PMU DT node to the device tree

[Bin Meng <bmeng.cn@gmail.com>]

On Fri, Jan 7, 2022 at 10:27 AM Atish Patra <atishp@rivosinc.com> wrote:
>
> Qemu virt machine can support few cache events and cycle/instret counters.
> It also supports counter overflow for these events.
>
> Add a DT node so that OpenSBI/Linux kernel is aware of the virt machine
> capabilities. There are some dummy nodes added for testing as well.
>
> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  hw/riscv/virt.c    | 38 ++++++++++++++++++++++++++++++++++++++
>  target/riscv/pmu.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
>  target/riscv/pmu.h |  1 +
>  3 files changed, 84 insertions(+)
>
> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
> index 3af074148ef4..99154199091c 100644
> --- a/hw/riscv/virt.c
> +++ b/hw/riscv/virt.c
> @@ -28,6 +28,7 @@
>  #include "hw/qdev-properties.h"
>  #include "hw/char/serial.h"
>  #include "target/riscv/cpu.h"
> +#include "target/riscv/pmu.h"
>  #include "hw/riscv/riscv_hart.h"
>  #include "hw/riscv/virt.h"
>  #include "hw/riscv/boot.h"
> @@ -406,6 +407,33 @@ static void create_fdt_socket_plic(RISCVVirtState *s,
>      g_free(plic_cells);
>  }
>
> +static void create_fdt_socket_pmu(RISCVVirtState *s,
> +                                  int socket, uint32_t *phandle,
> +                                  uint32_t *intc_phandles)
> +{
> +    int cpu;
> +    char *pmu_name;
> +    uint32_t *pmu_cells;
> +    MachineState *mc = MACHINE(s);
> +    RISCVCPU hart = s->soc[socket].harts[0];
> +
> +    pmu_cells = g_new0(uint32_t, s->soc[socket].num_harts * 2);
> +
> +    for (cpu = 0; cpu < s->soc[socket].num_harts; cpu++) {
> +        pmu_cells[cpu * 2 + 0] = cpu_to_be32(intc_phandles[cpu]);
> +        pmu_cells[cpu * 2 + 1] = cpu_to_be32(IRQ_PMU_OVF);
> +    }
> +
> +    pmu_name = g_strdup_printf("/soc/pmu");
> +    qemu_fdt_add_subnode(mc->fdt, pmu_name);
> +    qemu_fdt_setprop_string(mc->fdt, pmu_name, "compatible", "riscv,pmu");
> +    riscv_pmu_generate_fdt_node(mc->fdt, hart.cfg.pmu_num, pmu_name);
> +
> +    g_free(pmu_name);
> +    g_free(pmu_cells);
> +}
> +
> +
>  static void create_fdt_sockets(RISCVVirtState *s, const MemMapEntry *memmap,
>                                 bool is_32_bit, uint32_t *phandle,
>                                 uint32_t *irq_mmio_phandle,
> @@ -417,12 +445,20 @@ static void create_fdt_sockets(RISCVVirtState *s, const MemMapEntry *memmap,
>      uint32_t *intc_phandles;
>      MachineState *mc = MACHINE(s);
>      uint32_t xplic_phandles[MAX_NODES];
> +    RISCVCPU hart;
>
>      qemu_fdt_add_subnode(mc->fdt, "/cpus");
>      qemu_fdt_setprop_cell(mc->fdt, "/cpus", "timebase-frequency",
>                            RISCV_ACLINT_DEFAULT_TIMEBASE_FREQ);
>      qemu_fdt_setprop_cell(mc->fdt, "/cpus", "#size-cells", 0x0);
>      qemu_fdt_setprop_cell(mc->fdt, "/cpus", "#address-cells", 0x1);
> +
> +    /* Add the node for isa extensions discovery */
> +    qemu_fdt_add_subnode(mc->fdt, "/cpus/riscv,isa-ext");

Looks like the ongoing discussion does not support this idea
https://lore.kernel.org/linux-riscv/20211224211632.1698523-1-atishp@rivosinc.com/

> +    hart = s->soc[0].harts[0];
> +    if (hart.cfg.ext_sscof) {
> +        qemu_fdt_setprop(mc->fdt, "/cpus/riscv,isa-ext", "sscofpmf", NULL, 0);
> +    }
>      qemu_fdt_add_subnode(mc->fdt, "/cpus/cpu-map");
>
>      for (socket = (riscv_socket_count(mc) - 1); socket >= 0; socket--) {
> @@ -445,6 +481,8 @@ static void create_fdt_sockets(RISCVVirtState *s, const MemMapEntry *memmap,
>          create_fdt_socket_plic(s, memmap, socket, phandle,
>              intc_phandles, xplic_phandles);
>
> +        create_fdt_socket_pmu(s, socket, phandle, intc_phandles);
> +
>          g_free(intc_phandles);
>          g_free(clust_name);
>      }
> diff --git a/target/riscv/pmu.c b/target/riscv/pmu.c
> index 15f161059fb7..b58a09c85616 100644
> --- a/target/riscv/pmu.c
> +++ b/target/riscv/pmu.c
> @@ -19,11 +19,56 @@
>  #include "qemu/osdep.h"
>  #include "cpu.h"
>  #include "pmu.h"
> +#include "sysemu/device_tree.h"
>
>  #define RISCV_TIMEBASE_FREQ 1000000000 /* 1Ghz */
>  #define MAKE_32BIT_MASK(shift, length) \
>          (((uint32_t)(~0UL) >> (32 - (length))) << (shift))
>
> +/**
> + * To keep it simple, any event can be mapped to any programmable counters in
> + * QEMU. The generic cycle & instruction count events can also be monitored
> + * using programmable counters. In that case, mcycle & minstret must continue
> + * to provide the correct value as well. Hetergenous PMU per hart is not

typo of Heterogeneous

> + * supported yet. Thus, number of counters are same across all harts.
> + */
> +void riscv_pmu_generate_fdt_node(void *fdt, int num_ctrs, char *pmu_name)
> +{
> +    uint32_t fdt_event_ctr_map[20] = {};
> +    uint32_t cmask;
> +
> +    /* All the programmable counters can map to any event */
> +    cmask = MAKE_32BIT_MASK(3, num_ctrs);
> +
> +   /* SBI_PMU_HW_CPU_CYCLES */
> +   fdt_event_ctr_map[0] = cpu_to_be32(0x00000001);
> +   fdt_event_ctr_map[1] = cpu_to_be32(0x00000001);
> +   fdt_event_ctr_map[2] = cpu_to_be32(cmask | 1 << 0);
> +
> +   /* SBI_PMU_HW_INSTRUCTIONS */
> +   fdt_event_ctr_map[3] = cpu_to_be32(0x00000002);
> +   fdt_event_ctr_map[4] = cpu_to_be32(0x00000002);
> +   fdt_event_ctr_map[5] = cpu_to_be32(cmask | 1 << 2);
> +
> +   /* SBI_PMU_HW_CACHE_DTLB : READ : MISS */
> +   fdt_event_ctr_map[6] = cpu_to_be32(0x00010019);
> +   fdt_event_ctr_map[7] = cpu_to_be32(0x00010019);
> +   fdt_event_ctr_map[8] = cpu_to_be32(cmask);
> +
> +   /* SBI_PMU_HW_CACHE_DTLB : WRITE : MISS */
> +   fdt_event_ctr_map[9] = cpu_to_be32(0x0001001B);
> +   fdt_event_ctr_map[10] = cpu_to_be32(0x0001001B);
> +   fdt_event_ctr_map[11] = cpu_to_be32(cmask);
> +
> +   /* SBI_PMU_HW_CACHE_ITLB : READ : MISS */
> +   fdt_event_ctr_map[12] = cpu_to_be32(0x00010021);
> +   fdt_event_ctr_map[13] = cpu_to_be32(0x00010021);
> +   fdt_event_ctr_map[14] = cpu_to_be32(cmask);
> +
> +   qemu_fdt_setprop(fdt, pmu_name, "riscv,event-to-mhpmcounters",
> +                    fdt_event_ctr_map, sizeof(fdt_event_ctr_map));

Where is this documented? I can't find related discussion in the linux-riscv ML.

Please add some comment blocks to explain where these magic numbers
(like 0x00010021) come from.

> +}
> +
>  static bool riscv_pmu_counter_valid(RISCVCPU *cpu, uint32_t ctr_idx)
>  {
>      if (ctr_idx < 3 || ctr_idx >= RV_MAX_MHPMCOUNTERS ||
> diff --git a/target/riscv/pmu.h b/target/riscv/pmu.h
> index 9b400c3522f2..63c4b533b223 100644
> --- a/target/riscv/pmu.h
> +++ b/target/riscv/pmu.h
> @@ -31,6 +31,7 @@ int riscv_pmu_init(RISCVCPU *cpu, int num_counters);
>  int riscv_pmu_update_event_map(CPURISCVState *env, uint64_t value,
>                                 uint32_t ctr_idx);
>  int riscv_pmu_incr_ctr(RISCVCPU *cpu, enum riscv_pmu_event_idx event_idx);
> +void riscv_pmu_generate_fdt_node(void *fdt, int num_counters, char *pmu_name);
>  target_ulong get_icount_ticks(bool brv32);
>  int riscv_pmu_setup_timer(CPURISCVState *env, uint64_t value,
>                            uint32_t ctr_idx);
> --

Regards,
Bin