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Re: [Qemu-devel] [RFC PATCH 1/2] e1000: Use Address_Available bit as HW
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [RFC PATCH 1/2] e1000: Use Address_Available bit as HW latch |
Date: |
Thu, 21 Nov 2013 14:15:51 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 |
On 11/21/2013 01:04 PM, 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
s/he/the/
> 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 <address@hidden>
> ---
> hw/net/e1000.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
>
> - 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;
Does real hardware also auto-clear this bit when writing the low word
(thus forcing all drivers to write high word last to make a change take
effect)? Or are we risking the case of a driver that writes high word
first including the bit, and where real hardware just glitches over the
temporary half-written address where our emulation locks the user out
entirely? (Asked by someone that has not read the datasheet, so take
with a grain of salt)
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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