linux-kernel - [v5 PATCH] RISC-V: Fix unsupported isa string info.

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Message-Id: <20190807182316.28013-1-atish.patra@wdc.com>
Date:   Wed,  7 Aug 2019 11:23:16 -0700
From:   Atish Patra <atish.patra@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atish.patra@....com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Johan Hovold <johan@...nel.org>,
        linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: [v5 PATCH] RISC-V: Fix unsupported isa string info.

Currently, kernel prints a info warning if any of the extensions
from "mafdcsu" is missing in device tree. Here are few issues with
this approach.

1. It is not entirely correct as Linux can boot with "f or d"
extensions if kernel is configured accordingly.
2. It will continue to print the info string for future extensions
such as hypervisor as well which is completely misleading.
3. As per the RISC-V user level specification, S extension
can not exist in single letter extensions and must use multi-letter
strings. There are no U extension defined at all.
4. /proc/cpuinfo also doesn't print any other extensions except
"mafdcsu".

Fix this by making 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 are printed via
/proc/cpuinfo always.

Signed-off-by: Atish Patra <atish.patra@....com>
---
 arch/riscv/kernel/cpu.c | 49 +++++++++++++++++++++++++++++------------
 1 file changed, 35 insertions(+), 14 deletions(-)

diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
index 7da3c6a93abd..e521142e8ac3 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 = "mafdc";
 	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 +74,44 @@ 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
-	 * extension bits when they're in order. Hide the supervisor (S)
-	 * extension from userspace as it's not accessible from there.
+	 * RISC-V ISA strings define an order, so we only print all the
+	 * extension bits when they're in order. 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]) {
-			if (isa[0] != 's')
-				seq_write(f, isa, 1);
-
+	for (e = mandatory_ext; *e != '\0'; ++e) {
+		if (isa[0] != e[0]) {
+#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') {
+			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 +155,7 @@ 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