Re: [PATCH v2 1/3] hw/net: e1000: Correct the initial value of VET register

[Jason Wang <jasowang@redhat.com>]

在 2021/7/13 上午7:06, Bin Meng 写道:
> On Mon, Jul 5, 2021 at 1:57 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>> On Mon, Jul 5, 2021 at 12:21 PM Jason Wang <jasowang@redhat.com> wrote:
>>>
>>> 在 2021/7/2 下午5:24, Bin Meng 写道:
>>>> From: Christina Wang <christina.wang@windriver.com>
>>>>
>>>> The initial value of VLAN Ether Type (VET) register is 0x8100, as per
>>>> the manual and real hardware.
>>>>
>>>> While Linux e1000 driver always writes VET register to 0x8100, it is
>>>> not always the case for everyone. Drivers relying on the reset value
>>>> of VET won't be able to transmit and receive VLAN frames in QEMU.
>>>>
>>>> Reported-by: Markus Carlstedt <markus.carlstedt@windriver.com>
>>>> Signed-off-by: Christina Wang <christina.wang@windriver.com>
>>>> Signed-off-by: Bin Meng <bin.meng@windriver.com>
>>>> ---
>>>>
>>>> (no changes since v1)
>>>>
>>>>    hw/net/e1000.c | 2 ++
>>>>    1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
>>>> index 4f75b44cfc..20cbba6411 100644
>>>> --- a/hw/net/e1000.c
>>>> +++ b/hw/net/e1000.c
>>>> @@ -29,6 +29,7 @@
>>>>    #include "hw/pci/pci.h"
>>>>    #include "hw/qdev-properties.h"
>>>>    #include "migration/vmstate.h"
>>>> +#include "net/eth.h"
>>>>    #include "net/net.h"
>>>>    #include "net/checksum.h"
>>>>    #include "sysemu/sysemu.h"
>>>> @@ -254,6 +255,7 @@ static const uint32_t mac_reg_init[] = {
>>>>        [MANC]    = E1000_MANC_EN_MNG2HOST | E1000_MANC_RCV_TCO_EN |
>>>>                    E1000_MANC_ARP_EN | E1000_MANC_0298_EN |
>>>>                    E1000_MANC_RMCP_EN,
>>>> +    [VET]     = ETH_P_VLAN,
>>>
>>> I wonder if we need a compat flag for this, since we change the behavior.
>>>
>>> (See e1000_properties[])
>>>
>> No we don't need to since it does not break migration.
> Ping?


I admit migration "works" but it doesn't mean it's not broken. It 
changes the guest visible default value of VET register, so it may break 
things silently for the guest.

For old machine types, we should stick the value to the one without this 
fix.

Thanks


>