Re: [PATCH 1/1] Drivers: input: serio: New driver to support Hyper-V synthetic keyboard

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Mon, Sep 16, 2013 at 03:52:18PM +0000, KY Srinivasan wrote:
> 
> 
> > -----Original Message-----
> > From: Dmitry Torokhov [mailto:dmitry.torokhov@gmail.com]
> > Sent: Monday, September 16, 2013 8:20 AM
> > To: KY Srinivasan
> > Cc: gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org;
> > devel@linuxdriverproject.org; linux-input@vger.kernel.org; vojtech@suse.cz;
> > olaf@aepfle.de; apw@canonical.com; jasowang@redhat.com
> > Subject: Re: [PATCH 1/1] Drivers: input: serio: New driver to support Hyper-V
> > synthetic keyboard
> > 
> > Hi K. Y.
> > 
> > On Sun, Sep 15, 2013 at 10:28:54PM -0700, K. Y. Srinivasan wrote:
> > > Add a new driver to support synthetic keyboard. On the next generation
> > > Hyper-V guest firmware, many legacy devices will not be emulated and this
> > > driver will be required.
> > >
> > > I would like to thank Vojtech Pavlik <vojtech@suse.cz> for helping me with the
> > > details of the AT keyboard driver.
> > >
> > 
> > In addition to what Dan said:
> > 
> > > +
> > > +struct synth_kbd_protocol_response {
> > > +	struct synth_kbd_msg_hdr header;
> > > +	u32 accepted:1;
> > > +	u32 reserved:31;
> > > +};
> > 
> > Use of bitfields for on the wire structures makes me uneasy. I know that
> > currently you only going to run LE on LE, but still, maybe using
> > explicit shifts and masks would be better,
> 
> This definition of the data structure is defined by the host. I will see what I
> can do here.

You do not really need to change protocol, you just sat that accepted is
the bit 0 of the word and define endianness (LE in your case). Then you
do:

	struct synth_kbd_protocol_response {
		struct synth_kbd_msg_hdr header;
		__le32 status;
	}

	#define KBD_PROTOCOL_ACCEPTED BIT(0)

	...

	status = _le32_to_cpu(response->status);
	accepted = status & KBD_PROTOCOL_ACCEPTED;

Thanks.

-- 
Dmitry