[PATCH] hwmon: applesmc: avoid overlong udelay()

[Arnd Bergmann]

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 <a...@arndb.de>
---
 drivers/hwmon/applesmc.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index ec93b8d673f5..316618409315 100644
--- a/drivers/hwmon/applesmc.c
+++ b/drivers/hwmon/applesmc.c
@@ -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);
-- 
2.26.2