riscv: thead: Add th.sxstatus CSR emulation
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/blob/master/xtheadsxstatus.adoc
An important property of this patch is, that the th.sxstatus MAEE field
is not set (indicating that XTheadMae is not available).
XTheadMae 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 XTheadMae, so we need give kernels a mechanism to identify
if XTheadMae 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
Reviewed-by: LIU Zhiwei <zhiwe_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
Message-ID: <20240429073656.2486732-1-christoph.muellner@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 448dc95..e9d861e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -343,6 +343,7 @@
S: Supported
F: target/riscv/insn_trans/trans_xthead.c.inc
F: target/riscv/xthead*.decode
+F: target/riscv/th_*
F: disas/riscv-xthead*
RISC-V XVentanaCondOps extension
diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index abeb503..2946ac2 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -547,6 +547,7 @@
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 04ab0f1..12d8b53 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -826,4 +826,7 @@
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 a5e0734..a4bd61e 100644
--- a/target/riscv/meson.build
+++ b/target/riscv/meson.build
@@ -33,6 +33,7 @@
'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 0000000..6c970d4
--- /dev/null
+++ b/target/riscv/th_csr.c
@@ -0,0 +1,79 @@
+/*
+ * 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 smode(CPURISCVState *env, int csrno)
+{
+ if (riscv_has_ext(env, RVS)) {
+ 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", smode, 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);
+ }
+ }
+}
