From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:35670) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tsy0R-00078g-CR for qemu-devel@nongnu.org; Wed, 09 Jan 2013 10:55:58 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Tsy0K-0007Ew-KN for qemu-devel@nongnu.org; Wed, 09 Jan 2013 10:55:55 -0500 Received: from mx1.redhat.com ([209.132.183.28]:23456) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tsy0J-0007Eh-S4 for qemu-devel@nongnu.org; Wed, 09 Jan 2013 10:55:48 -0500 Date: Wed, 9 Jan 2013 17:34:07 +0200 From: "Michael S. Tsirkin" Message-ID: <20130109153407.GB7726@redhat.com> References: <20130109105100.GA17137@redhat.com> <50ED8C9D.1060109@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50ED8C9D.1060109@redhat.com> Subject: Re: [Qemu-devel] [PATCH] e1000: make ICS write-only List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jason Wang Cc: Anthony Liguori , wpaul@windriver.com, qemu-devel@nongnu.org, Stefan Hajnoczi , yan@daynix.com, Paolo Bonzini On Wed, Jan 09, 2013 at 11:28:29PM +0800, Jason Wang wrote: > On 01/09/2013 06:51 PM, Michael S. Tsirkin wrote: > > 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 > > --- > > 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); > > } > > > > If my memory is correct, though ICS is marked as read only in the spec, > we do can read it when I'm examining a real e1000 card. Interesting, this was not Bill's motivation. I haven't seen any reads with linux or windows guests - which guest did trigger them for you? Also, what's the value one would expect? -- MST