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

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Message-ID: <20151202172634.GA15531@dtor-ws>
Date:	Wed, 2 Dec 2015 09:26:34 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Sinclair Yeh <syeh@...are.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 Wed, Dec 02, 2015 at 07:31:24AM -0800, Greg Kroah-Hartman wrote:
> On Tue, Dec 01, 2015 at 06:21:06PM -0800, Sinclair Yeh wrote:
> > 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.
> 
> Use scripts/get_maintainer.pl, that's what it is there for.  A number of
> those patches should go through me, if not all of them, if you want them
> merged...
> 
> > 
> > This new macro is also used in arch/x86/kernel/cpu/vmware.c and
> > vmw_balloon.c
> 
> And it's used inconsistantly in those patches (you don't set the dummy
> variables to 0 in all of them...)  Now maybe that's just how the asm
> functions work, but it's not very obvious as to why this is at all.
> 
> > > > 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.
> 
> Why can't it go into vmw_vmci_defs.h instead, or your other .h file, why
> create yet-another-.h-file for your bus?  You already have 2, this would
> make it 3, which seems like a lot...

Umm, you are not saying that vmmouse should include vmci header file(s),
are you? Because the 2 are unrelated and vmci does not use the
hypervisor port to communicate with host IIRC.

Thanks.

-- 
Dmitry
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