Patchwork e1000: document ICS read behaviour

login
register
mail settings
Submitter Michael S. Tsirkin
Date Jan. 9, 2013, 10:01 p.m.
Message ID <20130109220122.GA12016@redhat.com>
Download mbox | patch
Permalink /patch/210880/
State New
Headers show

Comments

Michael S. Tsirkin - Jan. 9, 2013, 10:01 p.m.
Add code comment to clarify the reason we set ICS with ICR:
the reason was previously undocumented and git
log (commit b1332393cdd7d023de8f1f8aa136ee7866a18968)
confused rather than clarified the comments.
Digging in the mailing list archives gives the real reason
https://lists.gnu.org/archive/html/qemu-devel/2009-06/msg00401.html

Add code comment with an explanation supplied by Bill Paul.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/e1000.c | 11 +++++++++++
 1 file changed, 11 insertions(+)
Stefan Hajnoczi - Jan. 10, 2013, 8:26 a.m.
On Thu, Jan 10, 2013 at 12:01:22AM +0200, Michael S. Tsirkin wrote:
> Add code comment to clarify the reason we set ICS with ICR:
> the reason was previously undocumented and git
> log (commit b1332393cdd7d023de8f1f8aa136ee7866a18968)
> confused rather than clarified the comments.
> Digging in the mailing list archives gives the real reason
> https://lists.gnu.org/archive/html/qemu-devel/2009-06/msg00401.html
> 
> Add code comment with an explanation supplied by Bill Paul.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  hw/e1000.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)

Thanks, applied to the net tree:
https://github.com/stefanha/qemu/commits/net

Stefan
Michael S. Tsirkin - Jan. 10, 2013, 10:17 a.m.
On Thu, Jan 10, 2013 at 09:26:47AM +0100, Stefan Hajnoczi wrote:
> On Thu, Jan 10, 2013 at 12:01:22AM +0200, Michael S. Tsirkin wrote:
> > Add code comment to clarify the reason we set ICS with ICR:
> > the reason was previously undocumented and git
> > log (commit b1332393cdd7d023de8f1f8aa136ee7866a18968)
> > confused rather than clarified the comments.
> > Digging in the mailing list archives gives the real reason
> > https://lists.gnu.org/archive/html/qemu-devel/2009-06/msg00401.html
> > 
> > Add code comment with an explanation supplied by Bill Paul.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  hw/e1000.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> 
> Thanks, applied to the net tree:
> https://github.com/stefanha/qemu/commits/net
> 
> Stefan

Actually I'm going to send v2 with a minor tweak.
Stefan Hajnoczi - Jan. 10, 2013, 11:50 a.m.
On Thu, Jan 10, 2013 at 12:17:14PM +0200, Michael S. Tsirkin wrote:
> On Thu, Jan 10, 2013 at 09:26:47AM +0100, Stefan Hajnoczi wrote:
> > On Thu, Jan 10, 2013 at 12:01:22AM +0200, Michael S. Tsirkin wrote:
> > > Add code comment to clarify the reason we set ICS with ICR:
> > > the reason was previously undocumented and git
> > > log (commit b1332393cdd7d023de8f1f8aa136ee7866a18968)
> > > confused rather than clarified the comments.
> > > Digging in the mailing list archives gives the real reason
> > > https://lists.gnu.org/archive/html/qemu-devel/2009-06/msg00401.html
> > > 
> > > Add code comment with an explanation supplied by Bill Paul.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > ---
> > >  hw/e1000.c | 11 +++++++++++
> > >  1 file changed, 11 insertions(+)
> > 
> > Thanks, applied to the net tree:
> > https://github.com/stefanha/qemu/commits/net
> > 
> > Stefan
> 
> Actually I'm going to send v2 with a minor tweak.

No problem.  I will wait with the next net pull request until v2 has
been merged.

Stefan

Patch

diff --git a/hw/e1000.c b/hw/e1000.c
index 92fb00a..73e360e 100644
--- a/hw/e1000.c
+++ b/hw/e1000.c
@@ -230,7 +230,18 @@  set_interrupt_cause(E1000State *s, int index, uint32_t val)
         val |= E1000_ICR_INT_ASSERTED;
     }
     s->mac_reg[ICR] = val;
+
+    /*
+     * Make sure ICR and ICS registers have the same value.
+     * The spec says that the ICS register is write-only.  However in practice,
+     * on real hardware ICS is readable, and for reads it has the same value as
+     * ICR (except that ICS does not have the clear on read behaviour of ICR).
+     *
+     * The VxWorks PRO/1000 driver relies on this behaviour, so we have to
+     * emulate it.
+     */
     s->mac_reg[ICS] = val;
+
     qemu_set_irq(s->dev.irq[0], (s->mac_reg[IMS] & s->mac_reg[ICR]) != 0);
 }