From: Tony Lindgren <tony@atomide.com>
To: Nicolas Pitre <nico@fluxnic.net>
Cc: Stephen Boyd <sboyd@codeaurora.org>,
Greg Kroah-Hartman <gregkh@suse.de>,
linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Arnd Bergmann <arnd@arndb.de>,
Daniel Walker <dwalker@codeaurora.org>
Subject: Re: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
Date: Tue, 4 Jan 2011 10:49:04 -0800 [thread overview]
Message-ID: <20110104184904.GC7771@atomide.com> (raw)
In-Reply-To: <alpine.LFD.2.00.1012201638150.10437@xanadu.home>
* Nicolas Pitre <nico@fluxnic.net> [101220 13:38]:
> On Mon, 20 Dec 2010, Stephen Boyd wrote:
>
> > Without marking the asm __dcc_getstatus() volatile my compiler
> > decides it can cache the value of __ret in a register and then
> > check the value of it continually in hvc_dcc_put_chars() (I had
> > to replace get_wait/put_wait with 1 and fixup the branch
> > otherwise my disassembler barfed on __dcc_(get|put)char).
> >
> > 00000000 <hvc_dcc_put_chars>:
> > 0: ee103e11 mrc 14, 0, r3, cr0, cr1, {0}
> > 4: e3a0c000 mov ip, #0 ; 0x0
> > 8: e2033202 and r3, r3, #536870912 ; 0x20000000
> > c: ea000006 b 2c <hvc_dcc_put_chars+0x2c>
> > 10: e3530000 cmp r3, #0 ; 0x0
> > 14: 1afffffd bne 10 <hvc_dcc_put_chars+0x10>
> > 18: e7d1000c ldrb r0, [r1, ip]
> > 1c: ee10fe11 mrc 14, 0, pc, cr0, cr1, {0}
> > 20: 2afffffd bcs 1c <hvc_dcc_put_chars+0x1c>
> > 24: ee000e15 mcr 14, 0, r0, cr0, cr5, {0}
> > 28: e28cc001 add ip, ip, #1 ; 0x1
> > 2c: e15c0002 cmp ip, r2
> > 30: bafffff6 blt 10 <hvc_dcc_put_chars+0x10>
> > 34: e1a00002 mov r0, r2
> > 38: e12fff1e bx lr
> >
> > As you can see, the value of the mrc is checked against
> > DCC_STATUS_TX (bit 29) and then stored in r3 for later use.
> > Marking the asm volatile produces the following:
> >
> > 00000000 <hvc_dcc_put_chars>:
> > 0: e3a03000 mov r3, #0 ; 0x0
> > 4: ea000007 b 28 <hvc_dcc_put_chars+0x28>
> > 8: ee100e11 mrc 14, 0, r0, cr0, cr1, {0}
> > c: e3100202 tst r0, #536870912 ; 0x20000000
> > 10: 1afffffc bne 8 <hvc_dcc_put_chars+0x8>
> > 14: e7d10003 ldrb r0, [r1, r3]
> > 18: ee10fe11 mrc 14, 0, pc, cr0, cr1, {0}
> > 1c: 2afffffd bcs 18 <hvc_dcc_put_chars+0x18>
> > 20: ee000e15 mcr 14, 0, r0, cr0, cr5, {0}
> > 24: e2833001 add r3, r3, #1 ; 0x1
> > 28: e1530002 cmp r3, r2
> > 2c: bafffff5 blt 8 <hvc_dcc_put_chars+0x8>
> > 30: e1a00002 mov r0, r2
> > 34: e12fff1e bx lr
> >
> > which looks better and actually works. Mark all the inline
> > assembly in this file as volatile since we don't want the
> > compiler to optimize away these statements or move them around
> > in any way.
> >
> > Cc: Tony Lindgren <tony@atomide.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
> > Cc: Daniel Walker <dwalker@codeaurora.org>
> > Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
>
> Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Acked-by: Tony Lindgren <tony@atomide.com>
WARNING: multiple messages have this Message-ID (diff)
From: tony@atomide.com (Tony Lindgren)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
Date: Tue, 4 Jan 2011 10:49:04 -0800 [thread overview]
Message-ID: <20110104184904.GC7771@atomide.com> (raw)
In-Reply-To: <alpine.LFD.2.00.1012201638150.10437@xanadu.home>
* Nicolas Pitre <nico@fluxnic.net> [101220 13:38]:
> On Mon, 20 Dec 2010, Stephen Boyd wrote:
>
> > Without marking the asm __dcc_getstatus() volatile my compiler
> > decides it can cache the value of __ret in a register and then
> > check the value of it continually in hvc_dcc_put_chars() (I had
> > to replace get_wait/put_wait with 1 and fixup the branch
> > otherwise my disassembler barfed on __dcc_(get|put)char).
> >
> > 00000000 <hvc_dcc_put_chars>:
> > 0: ee103e11 mrc 14, 0, r3, cr0, cr1, {0}
> > 4: e3a0c000 mov ip, #0 ; 0x0
> > 8: e2033202 and r3, r3, #536870912 ; 0x20000000
> > c: ea000006 b 2c <hvc_dcc_put_chars+0x2c>
> > 10: e3530000 cmp r3, #0 ; 0x0
> > 14: 1afffffd bne 10 <hvc_dcc_put_chars+0x10>
> > 18: e7d1000c ldrb r0, [r1, ip]
> > 1c: ee10fe11 mrc 14, 0, pc, cr0, cr1, {0}
> > 20: 2afffffd bcs 1c <hvc_dcc_put_chars+0x1c>
> > 24: ee000e15 mcr 14, 0, r0, cr0, cr5, {0}
> > 28: e28cc001 add ip, ip, #1 ; 0x1
> > 2c: e15c0002 cmp ip, r2
> > 30: bafffff6 blt 10 <hvc_dcc_put_chars+0x10>
> > 34: e1a00002 mov r0, r2
> > 38: e12fff1e bx lr
> >
> > As you can see, the value of the mrc is checked against
> > DCC_STATUS_TX (bit 29) and then stored in r3 for later use.
> > Marking the asm volatile produces the following:
> >
> > 00000000 <hvc_dcc_put_chars>:
> > 0: e3a03000 mov r3, #0 ; 0x0
> > 4: ea000007 b 28 <hvc_dcc_put_chars+0x28>
> > 8: ee100e11 mrc 14, 0, r0, cr0, cr1, {0}
> > c: e3100202 tst r0, #536870912 ; 0x20000000
> > 10: 1afffffc bne 8 <hvc_dcc_put_chars+0x8>
> > 14: e7d10003 ldrb r0, [r1, r3]
> > 18: ee10fe11 mrc 14, 0, pc, cr0, cr1, {0}
> > 1c: 2afffffd bcs 18 <hvc_dcc_put_chars+0x18>
> > 20: ee000e15 mcr 14, 0, r0, cr0, cr5, {0}
> > 24: e2833001 add r3, r3, #1 ; 0x1
> > 28: e1530002 cmp r3, r2
> > 2c: bafffff5 blt 8 <hvc_dcc_put_chars+0x8>
> > 30: e1a00002 mov r0, r2
> > 34: e12fff1e bx lr
> >
> > which looks better and actually works. Mark all the inline
> > assembly in this file as volatile since we don't want the
> > compiler to optimize away these statements or move them around
> > in any way.
> >
> > Cc: Tony Lindgren <tony@atomide.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
> > Cc: Daniel Walker <dwalker@codeaurora.org>
> > Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
>
> Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Acked-by: Tony Lindgren <tony@atomide.com>
next prev parent reply other threads:[~2011-01-04 18:49 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-30 19:25 [PATCH] drivers: char: hvc: add arm JTAG DCC console support Daniel Walker
2010-11-30 19:25 ` Daniel Walker
2010-11-30 19:57 ` Nicolas Pitre
2010-11-30 19:57 ` Nicolas Pitre
2010-11-30 21:17 ` Arnd Bergmann
2010-11-30 21:17 ` Arnd Bergmann
2010-12-01 5:30 ` Stephen Boyd
2010-12-01 5:30 ` Stephen Boyd
2010-12-01 18:54 ` Daniel Walker
2010-12-01 18:54 ` Daniel Walker
2010-12-01 19:28 ` Greg KH
2010-12-01 19:28 ` Greg KH
2010-12-18 5:16 ` [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
2010-12-18 5:16 ` Stephen Boyd
2010-12-20 17:51 ` Daniel Walker
2010-12-20 17:51 ` Daniel Walker
2010-12-20 18:39 ` Stephen Boyd
2010-12-20 18:39 ` Stephen Boyd
2010-12-20 18:46 ` Nicolas Pitre
2010-12-20 18:46 ` Nicolas Pitre
2010-12-20 20:08 ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
2010-12-20 20:08 ` Stephen Boyd
2010-12-20 20:08 ` [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
2010-12-20 20:08 ` Stephen Boyd
2010-12-20 21:39 ` Nicolas Pitre
2010-12-20 21:39 ` Nicolas Pitre
2011-01-02 9:00 ` Pavel Machek
2011-01-02 9:00 ` Pavel Machek
2011-01-02 18:49 ` David Brown
2011-01-02 18:49 ` David Brown
2011-01-03 5:50 ` Pavel Machek
2011-01-03 5:50 ` Pavel Machek
2011-01-04 18:49 ` Tony Lindgren [this message]
2011-01-04 18:49 ` Tony Lindgren
2010-12-20 21:49 ` Arnaud Lacombe
2010-12-20 21:49 ` Arnaud Lacombe
2010-12-20 21:52 ` Stephen Boyd
2010-12-20 21:52 ` Stephen Boyd
2010-12-20 22:10 ` Nicolas Pitre
2010-12-20 22:10 ` Nicolas Pitre
2010-12-20 20:08 ` [PATCH 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops Stephen Boyd
2010-12-20 20:08 ` Stephen Boyd
2010-12-20 20:08 ` [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
2010-12-20 20:08 ` Stephen Boyd
2010-12-20 21:44 ` Nicolas Pitre
2010-12-20 21:44 ` Nicolas Pitre
2011-01-04 18:52 ` Tony Lindgren
2011-01-04 18:52 ` Tony Lindgren
2011-01-06 1:49 ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
2011-01-06 1:49 ` Stephen Boyd
2011-01-06 3:20 ` Greg KH
2011-01-06 3:20 ` Greg KH
2011-02-03 22:17 ` Greg KH
2011-02-03 22:17 ` Greg KH
2011-02-03 22:17 ` Greg KH
2011-02-03 23:19 ` Stephen Boyd
2011-02-03 23:19 ` Stephen Boyd
2011-02-03 23:30 ` Greg KH
2011-02-03 23:30 ` Greg KH
2011-02-03 23:48 ` [PATCHv2 " Stephen Boyd
2011-02-03 23:48 ` Stephen Boyd
2011-02-03 23:48 ` [PATCHv2 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
2011-02-03 23:48 ` Stephen Boyd
2011-02-03 23:48 ` [PATCHv2 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops Stephen Boyd
2011-02-03 23:48 ` Stephen Boyd
2011-02-03 23:48 ` [PATCHv2 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
2011-02-03 23:48 ` Stephen Boyd
2010-12-01 20:20 ` [PATCH] drivers: char: hvc: add arm JTAG DCC console support Stephen Boyd
2010-12-01 20:20 ` Stephen Boyd
2010-12-07 19:10 ` Stephen Boyd
2010-12-07 19:10 ` Stephen Boyd
2011-01-14 19:19 ` Tony Lindgren
2011-01-14 19:19 ` Tony Lindgren
2011-01-14 23:49 ` Stephen Boyd
2011-01-14 23:49 ` Stephen Boyd
2011-04-07 18:39 ` RONETIX - Asen Dimov
2011-04-07 18:39 ` RONETIX - Asen Dimov
2011-04-07 18:57 ` Mike Frysinger
2011-04-07 18:57 ` Mike Frysinger
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