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

[Bin Meng]

On Tue, Jul 13, 2021 at 3:03 PM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 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.

Could you please propose a solution on how to handle such a scenario
in a generic way in QEMU? (+Peter)

The POR reset value is wrong in QEMU and has carried forward the wrong
value for years, and correcting it to its right value needs to do
what?

Regards,
Bin