linux-kernel - [PATCH v4 3/5] efi/cper: Add a new helper function to print bitmasks

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Message-Id: <20250805-mauro_v3-v6-16-rev2-v4-3-ea538759841c@os.amperecomputing.com>
Date: Tue, 05 Aug 2025 11:35:40 -0700
From: Daniel Ferguson <danielf@...amperecomputing.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Jonathan Corbet <corbet@....net>, 
 "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, 
 James Morse <james.morse@....com>, Tony Luck <tony.luck@...el.com>, 
 Borislav Petkov <bp@...en8.de>, linux-doc@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org, 
 linux-efi@...r.kernel.org, linux-edac@...r.kernel.org, 
 Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Subject: [PATCH v4 3/5] efi/cper: Add a new helper function to print
 bitmasks

From: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>

Add a helper function to print a string with names associated
to each bit field.

A typical example is:

	const char * const bits[] = {
		"bit 3 name",
		"bit 4 name",
		"bit 5 name",
	};
	char str[120];
        unsigned int bitmask = BIT(3) | BIT(5);

	#define MASK  GENMASK(5,3)

	cper_bits_to_str(str, sizeof(str), FIELD_GET(MASK, bitmask),
			 bits, ARRAY_SIZE(bits));

The above code fills string "str" with "bit 3 name|bit 5 name".

Reviewed-by; Jonathan Cameron <Jonathan.Cameron@...wei.com>

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Acked-by: Borislav Petkov (AMD) <bp@...en8.de>
---
 drivers/firmware/efi/cper.c | 60 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/cper.h        |  2 ++
 2 files changed, 62 insertions(+)

diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
index 928409199a1a4009b11cf3189fe036ad8861169c..79ba688a64f8da7af2dad097b9331c72afc73864 100644
--- a/drivers/firmware/efi/cper.c
+++ b/drivers/firmware/efi/cper.c
@@ -12,6 +12,7 @@
  * Specification version 2.4.
  */
 
+#include <linux/bitmap.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/time.h>
@@ -106,6 +107,65 @@ void cper_print_bits(const char *pfx, unsigned int bits,
 		printk("%s\n", buf);
 }
 
+/**
+ * cper_bits_to_str - return a string for set bits
+ * @buf: buffer to store the output string
+ * @buf_size: size of the output string buffer
+ * @bits: bit mask
+ * @strs: string array, indexed by bit position
+ * @strs_size: size of the string array: @strs
+ *
+ * Add to @buf the bitmask in hexadecimal. Then, for each set bit in @bits,
+ * add the corresponding string describing the bit in @strs to @buf.
+ *
+ * A typical example is::
+ *
+ *	const char * const bits[] = {
+ *		"bit 3 name",
+ *		"bit 4 name",
+ *		"bit 5 name",
+ *	};
+ *	char str[120];
+ *	unsigned int bitmask = BIT(3) | BIT(5);
+ *	#define MASK GENMASK(5,3)
+ *
+ *	cper_bits_to_str(str, sizeof(str), FIELD_GET(MASK, bitmask),
+ *			 bits, ARRAY_SIZE(bits));
+ *
+ * The above code fills the string ``str`` with ``bit 3 name|bit 5 name``.
+ *
+ * Return: number of bytes stored or an error code if lower than zero.
+ */
+int cper_bits_to_str(char *buf, int buf_size, unsigned long bits,
+		     const char * const strs[], unsigned int strs_size)
+{
+	int len = buf_size;
+	char *str = buf;
+	int i, size;
+
+	*buf = '\0';
+
+	for_each_set_bit(i, &bits, strs_size) {
+		if (!(bits & BIT_ULL(i)))
+			continue;
+
+		if (*buf && len > 0) {
+			*str = '|';
+			len--;
+			str++;
+		}
+
+		size = strscpy(str, strs[i], len);
+		if (size < 0)
+			return size;
+
+		len -= size;
+		str += size;
+	}
+	return len - buf_size;
+}
+EXPORT_SYMBOL_GPL(cper_bits_to_str);
+
 static const char * const proc_type_strs[] = {
 	"IA32/X64",
 	"IA64",
diff --git a/include/linux/cper.h b/include/linux/cper.h
index 0ed60a91eca9d6425c9a41947a927b59f7aa2c71..58f40477c824e61c7f798978947bf1f441ce45ad 100644
--- a/include/linux/cper.h
+++ b/include/linux/cper.h
@@ -588,6 +588,8 @@ const char *cper_mem_err_type_str(unsigned int);
 const char *cper_mem_err_status_str(u64 status);
 void cper_print_bits(const char *prefix, unsigned int bits,
 		     const char * const strs[], unsigned int strs_size);
+int cper_bits_to_str(char *buf, int buf_size, unsigned long bits,
+		     const char * const strs[], unsigned int strs_size);
 void cper_mem_err_pack(const struct cper_sec_mem_err *,
 		       struct cper_mem_err_compact *);
 const char *cper_mem_err_unpack(struct trace_seq *,

-- 
2.50.0