From 0a6efab33eab4e973db26d9f90c3e97a7a82e399 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=utf8 Content-Transfer-Encoding: 8bit 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 --- 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..5849d2970bba 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; } /*----------------------------------------------------------------*/ -- 2.25.1