Re: [PATCH 1/1] Add virtio-input driver.

On Mon, 23 Mar 2015 16:05:29 +0100
Gerd Hoffmann [off-list ref] wrote:

On Mo, 2015-03-23 at 15:54 +0100, Michael S. Tsirkin wrote:

quoted

On Mon, Mar 23, 2015 at 03:27:35PM +0100, Gerd Hoffmann wrote:

quoted

  Hi,

quoted

quoted

quoted

quoted

You are doing leXXX everywhere, that's VERSION_1 dependency.
virtio_cread will do byteswaps differently without VERSION_1.
Just don't go there.

quoted

So to clarify, you dislike using __virtio32 in virtio input header?

Well, as I understand things __virtio32 implies byteorder depends on
whenever we are using VERSION_1 or not.  And non-transitional drivers
should not need it as everything is by definition little endian.

So, yes, your suggestion to just require VERSION_1 in the driver implies
in my eyes that there should be no reason to use __virtio32 instead of
__le32.

Or do I miss something here?

cheers,
  Gerd

You are right but then if you do require VERSION_1 then
__virtio32 becomes identical to __le32.

Except that sparse doesn't know that and throws errors when I mix the
two.

quoted

There's some runtime overhead as we check on each access,
but it shouldn't matter here, right?

Correct, config space is used at initialization time only.

quoted

I guess we could add virtio_cread_le - is this what
you'd like?

I just want something that makes both you and sparse happy.  I don't
care much whenever that is adding virtio_cread_le() or using __virtio32
even though it'll effectively is __le32 due to VERSION_1 being required.

I think it is clearer if you use __virtio32: The fact that virtio-input
is VERSION_1 only is not apparent from looking at the config space
definition, and explicitly forcing le accesses makes it look similar to
the oddballs like virtio-balloon. Just my two cents.