hwmon: (applesmc) avoid overlong udelay() (fff2d0f7) · Commits · 戴 / test

Building this driver with "clang -O3" produces a link error after the compiler partially unrolls the loop and 256ms becomes a compile-time constant that triggers the check in udelay(): ld.lld: error: undefined symbol: __bad_udelay >>> referenced by applesmc.c >>> hwmon/applesmc.o:(read_smc) in archive drivers/built-in.a I can see no reason against using a sleeping function here, as no part of the driver runs in atomic context, so instead use usleep_range() with a wide range and use jiffies for the end condition. Signed-off-by:

Arnd Bergmann <arnd@arndb.de> Link: https://lore.kernel.org/r/20200527135207.1118624-1-arnd@arndb.de Signed-off-by:

Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/applesmc.c

+9 −3

Original line number	Diff line number	Diff line
		@@ -156,14 +156,19 @@ static struct workqueue_struct *applesmc_led_wq;
		*/
		static int wait_read(void)
		{
		unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;
		u8 status;
		int us;

		for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
		udelay(us);
		usleep_range(us, us * 16);
		status = inb(APPLESMC_CMD_PORT);
		/* read: wait for smc to settle */
		if (status & 0x01)
		return 0;
		/* timeout: give up */
		if (time_after(jiffies, end))
		break;
		}

		pr_warn("wait_read() fail: 0x%02x\n", status);
		@@ -178,10 +183,11 @@ static int send_byte(u8 cmd, u16 port)
		{
		u8 status;
		int us;
		unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;

		outb(cmd, port);
		for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
		udelay(us);
		usleep_range(us, us * 16);
		status = inb(APPLESMC_CMD_PORT);
		/* write: wait for smc to settle */
		if (status & 0x02)
		@@ -190,7 +196,7 @@ static int send_byte(u8 cmd, u16 port)
		if (status & 0x04)
		return 0;
		/* timeout: give up */
		if (us << 1 == APPLESMC_MAX_WAIT)
		if (time_after(jiffies, end))
		break;
		/* busy: long wait and resend */
		udelay(APPLESMC_RETRY_WAIT);

Admin message