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rtc: cmos: avoid taking rtc_lock for extended period of time

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[ Upstream commit 0a6efab33eab4e973db26d9f90c3e97a7a82e399 ]

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.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Link: https://lore.kernel.org/r/Zxv8QWR21AV4ztC5@google.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Dmitry Torokhov 2024-10-25 13:14:57 -07:00 committed by Greg Kroah-Hartman
parent 80be263f3f
commit 2c9502ac83
1 changed files with 18 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
drivers/rtc/rtc-cmos.c
View File

@ -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 0;
}
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);
else if (can_bank2)
cmos_write_bank2(*buf++, off);
else
break;
}
spin_unlock_irq(&rtc_lock);
continue;
return count ? -EIO : 0;
guard(spinlock_irq)(&rtc_lock);
if (off < 128)
CMOS_WRITE(*buf, off);
else if (can_bank2)
cmos_write_bank2(*buf, off);
else
return -EIO;
}
return 0;
}
/*----------------------------------------------------------------*/