Re: [Qemu-devel] [RFC PATCH 1/2] e1000: Use Address_Available bit as HW latch

[Jason Wang <jasowang@redhat.com>]

On 11/22/2013 10:37 PM, Vlad Yasevich wrote:
> On 11/22/2013 04:47 AM, Jason Wang wrote:
>> > On 11/22/2013 04:04 AM, Vlad Yasevich wrote:
>>> >> e1000 provides a E1000_RAH_AV bit on every complete write
>>> >> to the Receive Address Register.  We can use this bit
>>> >> 2 ways:
>>> >>  1) To trigger HMP notifications.  When the bit is set the
>>> >>     mac address is fully set and we can update the HMP.
>>> >>
>>> >>  2) We can turn off he bit on the write to low order bits of
>>> >>     the Receive Address Register, so that we would not try
>>> >>     to match received traffic to this address when it is
>>> >>     not completely set.
>>> >>
>>> >> Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
>>> >> ---
>>> >>  hw/net/e1000.c | 11 ++++++++++-
>>> >>  1 file changed, 10 insertions(+), 1 deletion(-)
>>> >>
>>> >> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
>>> >> index ae63591..82978ea 100644
>>> >> --- a/hw/net/e1000.c
>>> >> +++ b/hw/net/e1000.c
>>> >> @@ -1106,10 +1106,19 @@ mac_writereg(E1000State *s, int index, uint32_t val)
>>> >>  
>>> >>      s->mac_reg[index] = val;
>>> >>  
>>> >> -    if (index == RA || index == RA + 1) {
>>> >> +    switch (index) {
>>> >> +    case RA:
>>> >> +        /* Mask off AV bit on the write of the low dword.  The write of
>>> >> +         * the high dword will set the bit.  This way a half-written
>>> >> +         * mac address will not be used to filter on rx.
>>> >> +         */
>>> >> +        s->mac_reg[RA+1] &= ~E1000_RAH_AV;
>> > 
>> > If a stupid driver write high dword first, it won't receive any packets.
> I need to ping Intel guys again.  I asked them what happens when only
> the low register is set, but haven't heard back.
>

They probably don't have the willing to share the internals of card. I
hacked the e1000 driver to check the subtle and undocumented behaviour
in the past. Maybe we can do the same.