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SubjectRe: [PATCH] hwmon: applesmc: avoid overlong udelay()
On Wed, May 27, 2020 at 03:51:57PM +0200, Arnd Bergmann wrote:
> 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.
>
Me not either.

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Applied.

Thanks,
Guenter

> ---
> 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);

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