linux-kernel - [PATCH] eeprom: idt_89hpesx: fix clang -Wformat warnings

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Date:   Fri,  1 Jul 2022 16:20:31 -0700
From:   Justin Stitt <justinstitt@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] eeprom: idt_89hpesx: fix clang -Wformat warnings

see warnings:
| drivers/misc/eeprom/idt_89hpesx.c:570:5: error: format specifies type
| 'unsigned char' but the argument has type 'u16' (aka 'unsigned short')
| [-Werror,-Wformat] memaddr);
-
| drivers/misc/eeprom/idt_89hpesx.c:579:5: error: format specifies type
| 'unsigned char' but the argument has type 'u16' (aka 'unsigned short')
| [-Werror,-Wformat] memaddr);
-
| drivers/misc/eeprom/idt_89hpesx.c:814:4: error: format specifies type
| 'unsigned short' but the argument has type 'unsigned int'
| [-Werror,-Wformat] CSR_REAL_ADDR(csraddr));

There's an ongoing movement to eventually enable the -Wformat flag for
clang. See: https://github.com/ClangBuiltLinux/linux/issues/378

The format specifier for idt_89hpesx.c:570 and 579 was `0x%02hhx`. The
part we care about `%hhx` describes a single byte format, wherein the
leftmost byte of our u16 type (of which memaddr is) is truncated.

example:
```
uint16_t x = 0xbabe;
printf("%hhx\n", x);
// output is: be
// we lost 'ba'
```

There exists a similar issue at idt_89hpesx.c:814 which involves the
CSR_REAL_ADDR macro. This macro returns a u16 but due to default
argument promotion for variadic functions (printf-like) actually
provides an int to the dev_err method.

My proposed solution is to expand the width of the format specifier to
fully encompass the provided argument (which is promoted to an int, see
below). I opted for '%x' as this specifies an unsigned hexadecimal
integer which, with a guarantee, can represent all the values of a u16.

As per C11 6.3.1.1:
(https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf)
`If an int can represent all values of the original type ..., the
value is converted to an int; otherwise, it is converted to an
unsigned int. These are called the integer promotions.`

Link: https://github.com/ClangBuiltLinux/linux/issues/378
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
 drivers/misc/eeprom/idt_89hpesx.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/eeprom/idt_89hpesx.c b/drivers/misc/eeprom/idt_89hpesx.c
index b0cff4b152da..42eac114edd7 100644
--- a/drivers/misc/eeprom/idt_89hpesx.c
+++ b/drivers/misc/eeprom/idt_89hpesx.c
@@ -566,7 +566,7 @@ static int idt_eeprom_read_byte(struct idt_89hpesx_dev *pdev, u16 memaddr,
 		eeseq.memaddr = cpu_to_le16(memaddr);
 		ret = pdev->smb_write(pdev, &smbseq);
 		if (ret != 0) {
-			dev_err(dev, "Failed to init eeprom addr 0x%02hhx",
+			dev_err(dev, "Failed to init eeprom addr 0x%02x",
 				memaddr);
 			break;
 		}
@@ -575,7 +575,7 @@ static int idt_eeprom_read_byte(struct idt_89hpesx_dev *pdev, u16 memaddr,
 		smbseq.bytecnt = EEPROM_RD_CNT;
 		ret = pdev->smb_read(pdev, &smbseq);
 		if (ret != 0) {
-			dev_err(dev, "Failed to read eeprom data 0x%02hhx",
+			dev_err(dev, "Failed to read eeprom data 0x%02x",
 				memaddr);
 			break;
 		}
@@ -810,7 +810,7 @@ static int idt_csr_read(struct idt_89hpesx_dev *pdev, u16 csraddr, u32 *data)
 	smbseq.bytecnt = CSR_RD_CNT;
 	ret = pdev->smb_read(pdev, &smbseq);
 	if (ret != 0) {
-		dev_err(dev, "Failed to read csr 0x%04hx",
+		dev_err(dev, "Failed to read csr 0x%04x",
 			CSR_REAL_ADDR(csraddr));
 		goto err_mutex_unlock;
 	}
-- 
2.37.0.rc0.161.g10f37bed90-goog