From: Dmitry Torokhov dmitry.torokhov@gmail.com
[ 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 --- 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 35dca2accbb8d..5849d2970bba4 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 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); + 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 0; }
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