Dnia 24 października 2024 22:37:08 CEST, Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> napisał/a:
>On my device reading entirety of /sys/devices/pnp0/00:03/cmos_nvram0/nvmem
>takes about 9 msec during which time interrupts are off on the CPU that
>does the read and the thread that performs the read can not be migrated
>or preempted by another higher priority thread (RT or not).
>
>Allow readers and writers be preempted by taking and releasing rtc_lock
>spinlock for each individual byte read or written rather than once per
>read/write request.
Hello,
A nice idea!
(sorry for any formatting problems, I'm on a train right now)
>
>Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
>---
> drivers/rtc/rtc-cmos.c | 31 +++++++++++++++----------------
> 1 file changed, 15 insertions(+), 16 deletions(-)
>
>diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
>index 35dca2accbb8..e8f2fe0d8560 100644
>--- a/drivers/rtc/rtc-cmos.c
>+++ b/drivers/rtc/rtc-cmos.c
>@@ -645,18 +645,17 @@ static int cmos_nvram_read(void *priv, unsigned int off, void *val,
> unsigned char *buf = val;
>
> off += NVRAM_OFFSET;
>- spin_lock_irq(&rtc_lock);
>- for (; count; count--, off++) {
>+ for (; count; count--, off++, buf++) {
>+ guard(spinlock_irq)(&rtc_lock);
> if (off < 128)
>- *buf++ = CMOS_READ(off);
>+ *buf = CMOS_READ(off);
> else if (can_bank2)
>- *buf++ = cmos_read_bank2(off);
>+ *buf = cmos_read_bank2(off);
> else
>- break;
>+ return -EIO;
> }
>- spin_unlock_irq(&rtc_lock);
>
>- return count ? -EIO : 0;
>+ return count;
return 0;
when you are at it.
> }
>
> static int cmos_nvram_write(void *priv, unsigned int off, void *val,
>@@ -671,23 +670,23 @@ static int cmos_nvram_write(void *priv, unsigned int off, void *val,
> * NVRAM to update, updating checksums is also part of its job.
> */
> off += NVRAM_OFFSET;
>- spin_lock_irq(&rtc_lock);
>- for (; count; count--, off++) {
>+ for (; count; count--, off++, buf++) {
> /* don't trash RTC registers */
> if (off == cmos->day_alrm
> || off == cmos->mon_alrm
> || off == cmos->century)
>- buf++;
>- else if (off < 128)
>- CMOS_WRITE(*buf++, off);
>+ continue;
>+
>+ guard(spinlock_irq)(&rtc_lock);
>+ if (off < 128)
>+ CMOS_WRITE(*buf, off);
> else if (can_bank2)
>- cmos_write_bank2(*buf++, off);
>+ cmos_write_bank2(*buf, off);
> else
>- break;
>+ return -EIO;
> }
>- spin_unlock_irq(&rtc_lock);
>
>- return count ? -EIO : 0;
>+ return count;
return 0;
> }
>
> /*----------------------------------------------------------------*/
