[PATCH v5] target/riscv: Add isa extenstion strings to the device tree

[Atish Patra <atishp@rivosinc.com>]

The Linux kernel parses the ISA extensions from "riscv,isa" DT
property. It used to parse only the single letter base extensions
until now. A generic ISA extension parsing framework was proposed[1]
recently that can parse multi-letter ISA extensions as well.

Generate the extended ISA string by appending  the available ISA extensions
to the "riscv,isa" string if it is enabled so that kernel can process it.

[1] https://lkml.org/lkml/2022/2/15/263

Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Suggested-by: Heiko Stubner <heiko@sntech.de>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
Changes from v4->v5:
1. Fixed the order of Zxx extensions.
2. Added a comment clearly describing the rules of extension order.

Changes from v3->v4:
1. Fixed the order of the extension names.
2. Added all the available ISA extensions in Qemu.

Changes from v2->v3:
1. Used g_strconcat to replace snprintf & a max isa string length as
suggested by Anup.
2. I have not included the Tested-by Tag from Heiko because the
implementation changed from v2 to v3.

Changes from v1->v2:
1. Improved the code redability by using arrays instead of individual check
---
 target/riscv/cpu.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index ddda4906ffb7..097c42f5c50f 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -34,6 +34,12 @@
 
 /* RISC-V CPU definitions */
 
+/* This includes the null terminated character '\0' */
+struct isa_ext_data {
+        const char *name;
+        bool enabled;
+};
+
 static const char riscv_exts[26] = "IEMAFDQCLBJTPVNSUHKORWXYZG";
 
 const char * const riscv_int_regnames[] = {
@@ -898,6 +904,60 @@ static void riscv_cpu_class_init(ObjectClass *c, void *data)
     device_class_set_props(dc, riscv_cpu_properties);
 }
 
+#define ISA_EDATA_ENTRY(name, prop) {#name, cpu->cfg.prop}
+
+static void riscv_isa_string_ext(RISCVCPU *cpu, char **isa_str, int max_str_len)
+{
+    char *old = *isa_str;
+    char *new = *isa_str;
+    int i;
+
+    /**
+     * Here are the ordering rules of extension naming defined by RISC-V
+     * specification :
+     * 1. All extensions should be separated from other multi-letter extensions
+     *    from other multi-letter extensions by an underscore.
+     * 2. The first letter following the 'Z' conventionally indicates the most
+     *    closely related alphabetical extension category, IMAFDQLCBKJTPVH.
+     *    If multiple 'Z' extensions are named, they should be ordered first
+     *    by category, then alphabetically within a category.
+     * 3. Standard supervisor-level extensions (starts with 'S') should be
+     *    listed after standard unprivileged extensions.  If multiple
+     *    supervisor-level extensions are listed, they should be ordered
+     *    alphabetically.
+     * 4. Non-standard extensions (starts with 'X') must be listed after all
+     *    standard extensions. They must be separated from other multi-letter
+     *    extensions by an underscore.
+     */
+    struct isa_ext_data isa_edata_arr[] = {
+        ISA_EDATA_ENTRY(zfh, ext_zfhmin),
+        ISA_EDATA_ENTRY(zfhmin, ext_zfhmin),
+        ISA_EDATA_ENTRY(zfinx, ext_zfinx),
+        ISA_EDATA_ENTRY(zdinx, ext_zdinx),
+        ISA_EDATA_ENTRY(zba, ext_zba),
+        ISA_EDATA_ENTRY(zbb, ext_zbb),
+        ISA_EDATA_ENTRY(zbc, ext_zbc),
+        ISA_EDATA_ENTRY(zbs, ext_zbs),
+        ISA_EDATA_ENTRY(zve32f, ext_zve32f),
+        ISA_EDATA_ENTRY(zve64f, ext_zve64f),
+        ISA_EDATA_ENTRY(zhinx, ext_zhinx),
+        ISA_EDATA_ENTRY(zhinxmin, ext_zhinxmin),
+        ISA_EDATA_ENTRY(svinval, ext_svinval),
+        ISA_EDATA_ENTRY(svnapot, ext_svnapot),
+        ISA_EDATA_ENTRY(svpbmt, ext_svpbmt),
+    };
+
+    for (i = 0; i < ARRAY_SIZE(isa_edata_arr); i++) {
+        if (isa_edata_arr[i].enabled) {
+            new = g_strconcat(old, "_", isa_edata_arr[i].name, NULL);
+            g_free(old);
+            old = new;
+        }
+    }
+
+    *isa_str = new;
+}
+
 char *riscv_isa_string(RISCVCPU *cpu)
 {
     int i;
@@ -910,6 +970,7 @@ char *riscv_isa_string(RISCVCPU *cpu)
         }
     }
     *p = '\0';
+    riscv_isa_string_ext(cpu, &isa_str, maxlen);
     return isa_str;
 }
 
-- 
2.30.2