From 2c9502ac832ab650528d50e14f8b752bf5175e5c Mon Sep 17 00:00:00 2001 From: Dmitry Torokhov Date: Fri, 25 Oct 2024 13:14:57 -0700 Subject: [PATCH] rtc: cmos: avoid taking rtc_lock for extended period of time MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit [ 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 Reviewed-by: Mateusz Jończyk Link: https://lore.kernel.org/r/Zxv8QWR21AV4ztC5@google.com Signed-off-by: Alexandre Belloni Signed-off-by: Sasha Levin --- drivers/rtc/rtc-cmos.c | 37 ++++++++++++++++++------------------- 1 file changed, 18 insertions(+), 19 deletions(-) diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c index 542568cd72b3..5f43773900d1 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); - 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; } /*----------------------------------------------------------------*/