From: Christoph Müllner <christoph.muell...@vrull.eu> The th.sxstatus CSR can be used to identify available custom extension on T-Head CPUs. The CSR is documented here: https://github.com/T-head-Semi/thead-extension-spec/pull/46
An important property of this patch is, that the th.sxstatus MAEE field is not set (indicating that XTheadMaee is not available). XTheadMaee is a memory attribute extension (similar to Svpbmt) which is implemented in many T-Head CPUs (C906, C910, etc.) and utilizes bits in PTEs that are marked as reserved. QEMU maintainers prefer to not implement XTheadMaee, so we need give kernels a mechanism to identify if XTheadMaee is available in a system or not. And this patch introduces this mechanism in QEMU in a way that's compatible with real HW (i.e., probing the th.sxstatus.MAEE bit). Further context can be found on the list: https://lists.gnu.org/archive/html/qemu-devel/2024-02/msg00775.html Signed-off-by: Christoph Müllner <christoph.muell...@vrull.eu> --- target/riscv/cpu.c | 1 + target/riscv/cpu.h | 3 ++ target/riscv/meson.build | 1 + target/riscv/th_csr.c | 78 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 83 insertions(+) create mode 100644 target/riscv/th_csr.c diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c index 193dbf7fe8..46a66cdbbb 100644 --- a/target/riscv/cpu.c +++ b/target/riscv/cpu.c @@ -545,6 +545,7 @@ static void rv64_thead_c906_cpu_init(Object *obj) cpu->cfg.mvendorid = THEAD_VENDOR_ID; #ifndef CONFIG_USER_ONLY set_satp_mode_max_supported(cpu, VM_1_10_SV39); + th_register_custom_csrs(cpu); #endif /* inherited from parent obj via riscv_cpu_init() */ diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h index 48e67410e1..8d0b500758 100644 --- a/target/riscv/cpu.h +++ b/target/riscv/cpu.h @@ -825,4 +825,7 @@ void riscv_cpu_register_gdb_regs_for_features(CPUState *cs); uint8_t satp_mode_max_from_map(uint32_t map); const char *satp_mode_str(uint8_t satp_mode, bool is_32_bit); +/* Implemented in th_csr.c */ +void th_register_custom_csrs(RISCVCPU *cpu); + #endif /* RISCV_CPU_H */ diff --git a/target/riscv/meson.build b/target/riscv/meson.build index a5e0734e7f..a4bd61e52a 100644 --- a/target/riscv/meson.build +++ b/target/riscv/meson.build @@ -33,6 +33,7 @@ riscv_system_ss.add(files( 'monitor.c', 'machine.c', 'pmu.c', + 'th_csr.c', 'time_helper.c', 'riscv-qmp-cmds.c', )) diff --git a/target/riscv/th_csr.c b/target/riscv/th_csr.c new file mode 100644 index 0000000000..66d260cabd --- /dev/null +++ b/target/riscv/th_csr.c @@ -0,0 +1,78 @@ +/* + * T-Head-specific CSRs. + * + * Copyright (c) 2024 VRULL GmbH + * + * 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 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 "cpu.h" +#include "cpu_vendorid.h" + +#define CSR_TH_SXSTATUS 0x5c0 + +/* TH_SXSTATUS bits */ +#define TH_SXSTATUS_UCME BIT(16) +#define TH_SXSTATUS_MAEE BIT(21) +#define TH_SXSTATUS_THEADISAEE BIT(22) + +typedef struct { + int csrno; + int (*insertion_test)(RISCVCPU *cpu); + riscv_csr_operations csr_ops; +} riscv_csr; + +static RISCVException s_mode_csr(CPURISCVState *env, int csrno) +{ + if (env->debugger) + return RISCV_EXCP_NONE; + + if (env->priv >= PRV_S) + return RISCV_EXCP_NONE; + + return RISCV_EXCP_ILLEGAL_INST; +} + +static int test_thead_mvendorid(RISCVCPU *cpu) +{ + if (cpu->cfg.mvendorid != THEAD_VENDOR_ID) + return -1; + return 0; +} + +static RISCVException read_th_sxstatus(CPURISCVState *env, int csrno, + target_ulong *val) +{ + /* We don't set MAEE here, because QEMU does not implement MAEE. */ + *val = TH_SXSTATUS_UCME | TH_SXSTATUS_THEADISAEE; + return RISCV_EXCP_NONE; +} + +static riscv_csr th_csr_list[] = { + { + .csrno = CSR_TH_SXSTATUS, + .insertion_test = test_thead_mvendorid, + .csr_ops = { "th.sxstatus", s_mode_csr, read_th_sxstatus } + } +}; + +void th_register_custom_csrs(RISCVCPU *cpu) +{ + for (size_t i = 0; i < ARRAY_SIZE(th_csr_list); i++) { + int csrno = th_csr_list[i].csrno; + riscv_csr_operations *csr_ops = &th_csr_list[i].csr_ops; + if (!th_csr_list[i].insertion_test(cpu)) + riscv_set_csr_ops(csrno, csr_ops); + } +} -- 2.44.0
