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Subject: Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Si-Wei Liu <si-wei.liu@oracle.com>, elic@nvidia.com,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <4ac87dc6-4629-78fa-c080-b4cd1eaaccb7@redhat.com>
Date:   Mon, 1 Mar 2021 11:53:04 +0800
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On 2021/3/1 5:30 上午, Michael S. Tsirkin wrote:
> On Wed, Feb 24, 2021 at 05:30:37PM +0800, Jason Wang wrote:
>> On 2021/2/24 4:43 下午, Michael S. Tsirkin wrote:
>>> On Wed, Feb 24, 2021 at 04:26:43PM +0800, Jason Wang wrote:
>>>>       Basically on first guest access QEMU would tell kernel whether
>>>>       guest is using the legacy or the modern interface.
>>>>       E.g. virtio_pci_config_read/virtio_pci_config_write will call ioctl(ENABLE_LEGACY, 1)
>>>>       while virtio_pci_common_read will call ioctl(ENABLE_LEGACY, 0)
>>>>
>>>>
>>>> But this trick work only for PCI I think?
>>>>
>>>> Thanks
>>> ccw has a revision it can check. mmio does not have transitional devices
>>> at all.
>>
>> Ok, then we can do the workaround in the qemu, isn't it?
>>
>> Thanks
> which one do you mean?


I meant the workaround that is done by 452639a64ad8 ("vdpa: make sure 
set_features is invoked for legacy").

Thanks


>