linux-kernel - Re: [PATCH 3/6] Input: Update vmmouse.c to use the common VMW

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Date:	Tue, 1 Dec 2015 14:45:27 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Sinclair Yeh <syeh@...are.com>
Cc:	X86 ML <x86@...nel.org>,
	"pv-drivers@...are.com" <pv-drivers@...are.com>,
	"linux-graphics-maintainer@...are.com" 
	<linux-graphics-maintainer@...are.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	virtualization@...ts.linux-foundation.org,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>
Subject: Re: [PATCH 3/6] Input: Update vmmouse.c to use the common VMW_PORT macros

On Tue, Dec 1, 2015 at 2:32 PM, Sinclair Yeh <syeh@...are.com> wrote:
> Hi,
>
> On Tue, Dec 01, 2015 at 02:24:14PM -0800, Dmitry Torokhov wrote:
>> On Tue, Dec 01, 2015 at 02:18:49PM -0800, Sinclair Yeh wrote:
>> > v2:
>> > Instead of replacing existing VMMOUSE defines, only modify enough
>> > to use the new VMW_PORT define.
>> >
>> > v3:
>> > Use updated VMWARE_PORT() which requires hypervisor magic as an added
>> > parameter
>> >
>> > Signed-off-by: Sinclair Yeh <syeh@...are.com>
>> > Reviewed-by: Thomas Hellstrom <thellstrom@...are.com>
>> > Reviewed-by: Alok N Kataria <akataria@...are.com>
>> > Cc: pv-drivers@...are.com
>> > Cc: linux-graphics-maintainer@...are.com
>> > Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>
>> > Cc: Arnd Bergmann <arnd@...db.de>
>> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> > Cc: linux-kernel@...r.kernel.org
>> > Cc: virtualization@...ts.linux-foundation.org
>> > Cc: linux-input@...r.kernel.org
>> > ---
>> >  drivers/input/mouse/vmmouse.c | 22 +++++++---------------
>> >  1 file changed, 7 insertions(+), 15 deletions(-)
>> >
>> > diff --git a/drivers/input/mouse/vmmouse.c b/drivers/input/mouse/vmmouse.c
>> > index e272f06..d34e3e4 100644
>> > --- a/drivers/input/mouse/vmmouse.c
>> > +++ b/drivers/input/mouse/vmmouse.c
>> > @@ -19,6 +19,7 @@
>> >  #include <linux/slab.h>
>> >  #include <linux/module.h>
>> >  #include <asm/hypervisor.h>
>> > +#include <asm/vmware.h>
>> >
>> >  #include "psmouse.h"
>> >  #include "vmmouse.h"
>> > @@ -84,21 +85,12 @@ struct vmmouse_data {
>> >   * implementing the vmmouse protocol. Should never execute on
>> >   * bare metal hardware.
>> >   */
>> > -#define VMMOUSE_CMD(cmd, in1, out1, out2, out3, out4)      \
>> > -({                                                 \
>> > -   unsigned long __dummy1, __dummy2;               \
>> > -   __asm__ __volatile__ ("inl %%dx" :              \
>> > -           "=a"(out1),                             \
>> > -           "=b"(out2),                             \
>> > -           "=c"(out3),                             \
>> > -           "=d"(out4),                             \
>> > -           "=S"(__dummy1),                         \
>> > -           "=D"(__dummy2) :                        \
>> > -           "a"(VMMOUSE_PROTO_MAGIC),               \
>> > -           "b"(in1),                               \
>> > -           "c"(VMMOUSE_PROTO_CMD_##cmd),           \
>> > -           "d"(VMMOUSE_PROTO_PORT) :               \
>> > -           "memory");                              \
>> > +#define VMMOUSE_CMD(cmd, in1, out1, out2, out3, out4)                 \
>> > +({                                                            \
>> > +   unsigned long __dummy1 = 0, __dummy2 = 0;                  \
>>
>> Why do we need to initialize dummies?
>
> Because for some commands those parameters to VMW_PORT() can be both
> input and outout.

The vmmouse commands do not use them as input though, so it seems we
are simply wasting CPU cycles setting them to 0 just because we are
using the new VMW_PORT here. Why do we need to switch? What is the
benefit of doing this?

Thanks.

-- 
Dmitry
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