From 83ad95957c7e66f2685fb38c9675949d3bf478eb Mon Sep 17 00:00:00 2001 From: Alexander Graf Date: Tue, 19 Nov 2019 13:20:27 +0000 Subject: [PATCH] pl031: Expose RTCICR as proper WC register The current PL031 RTCICR register implementation always clears the IRQ pending status on a register write, regardless of the value the guest writes. To justify that behavior, it references the ARM926EJ-S Development Chip Reference Manual (DDI0287B) and indicates that said document states that any write clears the internal IRQ state. It is indeed true that in section 11.1 this document says: "The interrupt is cleared by writing any data value to the interrupt clear register RTCICR". However, later in section 11.2.2 it contradicts itself by saying: "Writing 1 to bit 0 of RTCICR clears the RTCINTR flag." The latter statement matches the PL031 TRM (DDI0224C), which says: "Writing 1 to bit position 0 clears the corresponding interrupt. Writing 0 has no effect." Let's assume that the self-contradictory DDI0287B is in error, and follow the reference manual for the device itself, by making the register write-one-to-clear. Reported-by: Hendrik Borghorst Signed-off-by: Alexander Graf Message-id: 20191104115228.30745-1-graf@amazon.com [PMM: updated commit message to note that DDI0287B says two conflicting things] Reviewed-by: Peter Maydell Signed-off-by: Peter Maydell --- hw/rtc/pl031.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/hw/rtc/pl031.c b/hw/rtc/pl031.c index 3a982752a2..c57cf83165 100644 --- a/hw/rtc/pl031.c +++ b/hw/rtc/pl031.c @@ -149,11 +149,7 @@ static void pl031_write(void * opaque, hwaddr offset, pl031_update(s); break; case RTC_ICR: - /* The PL031 documentation (DDI0224B) states that the interrupt is - cleared when bit 0 of the written value is set. However the - arm926e documentation (DDI0287B) states that the interrupt is - cleared when any value is written. */ - s->is = 0; + s->is &= ~value; pl031_update(s); break; case RTC_CR: