[PATCH v4 3/4] RISC-V: Fix unsupported isa string info.

[Atish Patra]

Currently, kernel prints a info warning if any of the extensions
from "mafdcsu" is missing in device tree. This is not entirely
correct as Linux can boot with "f or d" extensions if kernel is
configured accordingly. Moreover, it will continue to print the
info string for future extensions such as hypervisor as well which
is misleading. /proc/cpuinfo also doesn't print any other extensions
except "mafdcsu".

Make sure that info log is only printed only if kernel is configured
to have any mandatory extensions but device tree doesn't describe it.
All the extensions present in device tree and follow the order
described in the RISC-V specification (except 'S') are printed via
/proc/cpuinfo always.

Signed-off-by: Atish Patra <atish.patra@xxxxxxx>
---
 arch/riscv/kernel/cpu.c | 47 ++++++++++++++++++++++++++++++++---------
 1 file changed, 37 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
index 7da3c6a93abd..9b1d4550fbe6 100644
--- a/arch/riscv/kernel/cpu.c
+++ b/arch/riscv/kernel/cpu.c
@@ -7,6 +7,7 @@
 #include <linux/seq_file.h>
 #include <linux/of.h>
 #include <asm/smp.h>
+#include <asm/hwcap.h>
 
 /*
  * Returns the hart ID of the given device tree node, or -ENODEV if the node
@@ -46,11 +47,14 @@ int riscv_of_processor_hartid(struct device_node *node)
 
 #ifdef CONFIG_PROC_FS
 
-static void print_isa(struct seq_file *f, const char *orig_isa)
+static void print_isa(struct seq_file *f, const char *orig_isa,
+		      unsigned long cpuid)
 {
-	static const char *ext = "mafdcsu";
+	static const char *mandatory_ext = "mafdcsu";
 	const char *isa = orig_isa;
 	const char *e;
+	char unsupported_isa[26] = {0};
+	int index = 0;
 
 	/*
 	 * Linux doesn't support rv32e or rv128i, and we only support booting
@@ -70,27 +74,50 @@ static void print_isa(struct seq_file *f, const char *orig_isa)
 	isa += 5;
 
 	/*
-	 * Check the rest of the ISA string for valid extensions, printing those
-	 * we find.  RISC-V ISA strings define an order, so we only print the
+	 * RISC-V ISA strings define an order, so we only print all the
 	 * extension bits when they're in order. Hide the supervisor (S)
 	 * extension from userspace as it's not accessible from there.
+	 * Throw a warning only if any mandatory extensions are not available
+	 * and kernel is configured to have that mandatory extensions.
 	 */
-	for (e = ext; *e != '\0'; ++e) {
-		if (isa[0] == e[0]) {
+	for (e = mandatory_ext; *e != '\0'; ++e) {
+		if (isa[0] != e[0]) {
+#if defined(CONFIG_ISA_RISCV_C)
+			if (isa[0] == 'c')
+				continue;
+#endif
+#if defined(CONFIG_FP)
+			if ((isa[0] == 'f') || (isa[0] == 'd'))
+				continue;
+#endif
+			unsupported_isa[index] = e[0];
+			index++;
+		}
+		/* Only write if part of isa string */
+		if (isa[0] != '\0') {
 			if (isa[0] != 's')
 				seq_write(f, isa, 1);
-
 			isa++;
 		}
 	}
+	if (isa[0] != '\0') {
+		/* Add remainging isa strings */
+		for (e = isa; *e != '\0'; ++e) {
+#if !defined(CONFIG_VIRTUALIZATION)
+			if (e[0] != 'h')
+#endif
+				seq_write(f, e, 1);
+		}
+	}
 	seq_puts(f, "\n");
 
 	/*
 	 * If we were given an unsupported ISA in the device tree then print
 	 * a bit of info describing what went wrong.
 	 */
-	if (isa[0] != '\0')
-		pr_info("unsupported ISA \"%s\" in device tree\n", orig_isa);
+	if (unsupported_isa[0])
+		pr_info("unsupported ISA extensions \"%s\" in device tree for cpu [%ld]\n",
+			unsupported_isa, cpuid);
 }
 
 static void print_mmu(struct seq_file *f, const char *mmu_type)
@@ -134,7 +161,7 @@ static int c_show(struct seq_file *m, void *v)
 	seq_printf(m, "processor\t: %lu\n", cpu_id);
 	seq_printf(m, "hart\t\t: %lu\n", cpuid_to_hartid_map(cpu_id));
 	if (!of_property_read_string(node, "riscv,isa", &isa))
-		print_isa(m, isa);
+		print_isa(m, isa, cpu_id);
 	if (!of_property_read_string(node, "mmu-type", &mmu))
 		print_mmu(m, mmu);
 	if (!of_property_read_string(node, "compatible", &compat)
-- 
2.21.0