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From:   Conor Dooley <conor.dooley@microchip.com>
To:     <palmer@dabbelt.com>
CC:     <conor@kernel.org>, <conor.dooley@microchip.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Andrew Jones <ajones@ventanamicro.com>,
        Heiko Stuebner <heiko.stuebner@vrull.eu>,
        "Evan Green" <evan@rivosinc.com>,
        Sunil V L <sunilvl@ventanamicro.com>,
        <linux-riscv@lists.infradead.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: [PATCH v2 08/10] RISC-V: enable extension detection from new properties
Date:   Thu, 29 Jun 2023 09:28:54 +0100
Message-ID: <20230629-defiling-salary-a51c0d89d31c@wendy>
In-Reply-To: <20230629-rebuttal-vagueness-a699deb7c7b3@wendy>
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Add support for parsing the new riscv,isa-extensions property in
riscv_fill_hwcap(), by means of a new "property" member of the
riscv_isa_ext_data struct. For now, this shadows the name of the
extension for all users, however this may not be the case for all
extensions, based on how the dt-binding is written.
For the sake of backwards compatibility, fall back to the old scheme
if the new properties are not detected. For now, just inform, rather
than warn, when that happens.

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
Changes in v2:
- Pick a more suitable function name than fill_hwcap_new()
- Actually use the property member to read from the DT
---
 arch/riscv/include/asm/hwcap.h |  1 +
 arch/riscv/kernel/cpufeature.c | 76 ++++++++++++++++++++++++++++++++--
 2 files changed, 73 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index a20e4ade1b53..e3cda14a486b 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -76,6 +76,7 @@ unsigned long riscv_get_elf_hwcap(void);
 struct riscv_isa_ext_data {
 	const unsigned int id;
 	const char *name;
+	const char *property;
 };
 
 extern const struct riscv_isa_ext_data riscv_isa_ext[];
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 41aedeaecb61..2c4503fa984f 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -101,6 +101,7 @@ static bool riscv_isa_extension_check(int id)
 
 #define __RISCV_ISA_EXT_DATA(_name, _id) {	\
 	.name = #_name,				\
+	.property = #_name,			\
 	.id = _id,				\
 }
 
@@ -414,11 +415,67 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
 		acpi_put_table((struct acpi_table_header *)rhct);
 }
 
+static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
+{
+	unsigned int cpu;
+
+	for_each_possible_cpu(cpu) {
+		unsigned long this_hwcap = 0;
+		struct device_node *cpu_node;
+		DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);
+
+		cpu_node = of_cpu_device_node_get(cpu);
+		if (!cpu_node) {
+			pr_warn("Unable to find cpu node\n");
+			continue;
+		}
+
+		if (!of_property_present(cpu_node, "riscv,isa-extensions"))
+			continue;
+
+		for (int i = 0; i < riscv_isa_ext_count; i++) {
+			if (of_property_match_string(cpu_node, "riscv,isa-extensions",
+						     riscv_isa_ext[i].property) < 0)
+				continue;
+
+			if (!riscv_isa_extension_check(riscv_isa_ext[i].id))
+				continue;
+
+			/* Only single letter extensions get set in hwcap */
+			if (strnlen(riscv_isa_ext[i].name, 2) == 1)
+				this_hwcap |= isa2hwcap[riscv_isa_ext[i].id];
+
+			set_bit(riscv_isa_ext[i].id, this_isa);
+		}
+
+		of_node_put(cpu_node);
+
+		/*
+		 * All "okay" harts should have same isa. Set HWCAP based on
+		 * common capabilities of every "okay" hart, in case they don't.
+		 */
+		if (elf_hwcap)
+			elf_hwcap &= this_hwcap;
+		else
+			elf_hwcap = this_hwcap;
+
+		if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
+			bitmap_copy(riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
+		else
+			bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
+	}
+
+	if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
+		return -ENOENT;
+
+	return 0;
+}
+
 void __init riscv_fill_hwcap(void)
 {
 	char print_str[NUM_ALPHA_EXTS + 1];
-	int i, j;
 	unsigned long isa2hwcap[26] = {0};
+	int i, j;
 
 	isa2hwcap['i' - 'a'] = COMPAT_HWCAP_ISA_I;
 	isa2hwcap['m' - 'a'] = COMPAT_HWCAP_ISA_M;
@@ -428,10 +485,21 @@ void __init riscv_fill_hwcap(void)
 	isa2hwcap['c' - 'a'] = COMPAT_HWCAP_ISA_C;
 	isa2hwcap['v' - 'a'] = COMPAT_HWCAP_ISA_V;
 
-	riscv_fill_hwcap_from_isa_string(isa2hwcap);
+	if (!acpi_disabled) {
+		riscv_fill_hwcap_from_isa_string(isa2hwcap);
+	} else {
+		int ret = riscv_fill_hwcap_from_ext_list(isa2hwcap);
 
-	/* We don't support systems with F but without D, so mask those out
-	 * here. */
+		if (ret) {
+			pr_info("Falling back to deprecated \"riscv,isa\"\n");
+			riscv_fill_hwcap_from_isa_string(isa2hwcap);
+		}
+	}
+
+	/*
+	 * We don't support systems with F but without D, so mask those out
+	 * here.
+	 */
 	if ((elf_hwcap & COMPAT_HWCAP_ISA_F) && !(elf_hwcap & COMPAT_HWCAP_ISA_D)) {
 		pr_info("This kernel does not support systems with F but not D\n");
 		elf_hwcap &= ~COMPAT_HWCAP_ISA_F;
-- 
2.40.1