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

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Date:	Tue, 1 Dec 2015 18:21:06 -0800
From:	"Sinclair Yeh" <syeh@...are.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	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>,
	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 01, 2015 at 04:04:08PM -0800, Greg Kroah-Hartman wrote:
> On Tue, Dec 01, 2015 at 02:54:20PM -0800, Sinclair Yeh wrote:
> > 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@...are.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.
> 
> But the macro is only used here, and the variables aren't used at all,
> so it makes no sense in this file.

Maybe it's because I didn't CC you on the rest of the series.  I wasn't
sure what the proper distribution list is for each part.

This new macro is also used in arch/x86/kernel/cpu/vmware.c and
vmw_balloon.c


> 
> > The second reason is this organization makes some on-going future
> > development easier.
> 
> We don't plan for "future" development other than a single patch series,
> as we have no idea what that development is, nor if it will really
> happen.  You can always change this file later if you need to, nothing
> is keeping that from happening.

So the intent of this series is to centralize similar lines of inline
assembly code that are currently used by 3 different kernel modules
to a central place.  The new vmware.h [patch 0/6] becomes the one header
to include for common guest-host communication needs.


> thanks,
> 
> greg k-h
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