Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S932141AbbLAWxB (ORCPT <rfc822;w@1wt.eu>);
	Tue, 1 Dec 2015 17:53:01 -0500
Received: from smtp-outbound-1.vmware.com ([208.91.2.12]:42953 "EHLO
	smtp-outbound-1.vmware.com" rhost-flags-OK-OK-OK-OK)
	by vger.kernel.org with ESMTP id S1757085AbbLAWw7 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 1 Dec 2015 17:52:59 -0500
From: "Sinclair Yeh" <syeh@vmware.com>
Date: Tue, 1 Dec 2015 14:54:20 -0800
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: X86 ML <x86@kernel.org>, "pv-drivers@vmware.com" <pv-drivers@vmware.com>,
        "linux-graphics-maintainer@vmware.com" 
	<linux-graphics-maintainer@vmware.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        lkml <linux-kernel@vger.kernel.org>,
        virtualization@lists.linux-foundation.org,
        "linux-input@vger.kernel.org" <linux-input@vger.kernel.org>
Subject: Re: [PATCH 3/6] Input: Update vmmouse.c to use the common VMW_PORT
 macros
Message-ID: <20151201225420.GA11210@syeh-linux>
References: <1449008047-8252-1-git-send-email-syeh@vmware.com>
 <1449008332-9394-1-git-send-email-syeh@vmware.com>
 <1449008332-9394-3-git-send-email-syeh@vmware.com>
 <20151201222414.GH3740@dtor-ws>
 <20151201223255.GA10753@syeh-linux>
 <CAKdAkRTVJ_DWD6uYhp+qd1uYwe3rPguDFAMXpa5=8CwVuO16NQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAKdAkRTVJ_DWD6uYhp+qd1uYwe3rPguDFAMXpa5=8CwVuO16NQ@mail.gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 2285
Lines: 55

Hi,

On Tue, Dec 01, 2015 at 02:45:27PM -0800, Dmitry Torokhov wrote:
> On Tue, Dec 1, 2015 at 2:32 PM, Sinclair Yeh <syeh@vmware.com> wrote:
> > Hi,
> >

<snip>

> >> >   */
> >> > -#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?

There are two reasons.  One is to make the code more readable and
maintainable.  Rather than having mostly similar inline assembly
code sprinkled across multiple modules, we can just use the macros
and document that.

The second reason is this organization makes some on-going future
development easier.

Hope this helps.

Sinclair
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/