From patchwork Wed Jan 9 10:51:00 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: e1000: make ICS write-only Date: Wed, 09 Jan 2013 00:51:00 -0000 From: "Michael S. Tsirkin" X-Patchwork-Id: 210689 Message-Id: <20130109105100.GA17137@redhat.com> To: qemu-devel@nongnu.org, wpaul@windriver.com, yan@daynix.com Cc: Paolo Bonzini , Anthony Liguori , Jason Wang , Stefan Hajnoczi , "Michael S. Tsirkin" Since commit b1332393cdd7d023de8f1f8aa136ee7866a18968, qemu started updating ICS register when interrupt is sent, with the intent to match spec better (guests do not actually read this register). However, the function set_interrupt_cause where ICS is updated is often called internally by device emulation so reading it does not produce the last value written by driver. Looking closer at the spec, it documents ICS as write-only, so there's no need to update it at all. I conclude that while harmless this line is useless code so removing it is a bit cleaner than keeping it in. Tested with windows and linux guests. Cc: Bill Paul Reported-by: Yan Vugenfirer Signed-off-by: Michael S. Tsirkin Reviewed-by: Anthony Liguori --- hw/e1000.c | 1 - 1 file changed, 1 deletion(-) diff --git a/hw/e1000.c b/hw/e1000.c index 92fb00a..928d804 100644 --- a/hw/e1000.c +++ b/hw/e1000.c @@ -230,7 +230,6 @@ set_interrupt_cause(E1000State *s, int index, uint32_t val) val |= E1000_ICR_INT_ASSERTED; } s->mac_reg[ICR] = val; - s->mac_reg[ICS] = val; qemu_set_irq(s->dev.irq[0], (s->mac_reg[IMS] & s->mac_reg[ICR]) != 0); }