From: Nicolas Pitre <nico@fluxnic.net> To: Stephen Boyd <sboyd@codeaurora.org> Cc: Greg Kroah-Hartman <gregkh@suse.de>, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Tony Lindgren <tony@atomide.com>, Arnd Bergmann <arnd@arndb.de>, Daniel Walker <dwalker@codeaurora.org> Subject: Re: [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Date: Mon, 20 Dec 2010 16:44:56 -0500 (EST) [thread overview] Message-ID: <alpine.LFD.2.00.1012201644110.10437@xanadu.home> (raw) In-Reply-To: <1292875718-7980-4-git-send-email-sboyd@codeaurora.org> On Mon, 20 Dec 2010, Stephen Boyd wrote: > The inline assembly differences for v6 vs. v7 in the hvc_dcc > driver are purely optimizations. On a v7 processor, an mrc with > the pc sets the condition codes to the 28-31 bits of the register > being read. It just so happens that the TX/RX full bits the DCC > driver is testing for are high enough in the register to be put > into the condition codes. On a v6 processor, this "feature" isn't > implemented and thus we have to do the usual read, mask, test > operations to check for TX/RX full. > > Since we already test the RX/TX full bits before calling > __dcc_getchar() and __dcc_putchar() we don't actually need to do > anything special for v7 over v6. The only difference is in > hvc_dcc_get_chars(). We would test RX full, poll RX full, and > then read a character from the buffer, whereas now we will test > RX full, read a character from the buffer, and then test RX full > again for the second iteration of the loop. It doesn't seem > possible for the buffer to go from full to empty between testing > the RX full and reading a character. Therefore, replace the v7 > versions with the v6 versions and everything works the same. > > 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> > --- > drivers/char/hvc_dcc.c | 24 ------------------------ > 1 files changed, 0 insertions(+), 24 deletions(-) > > diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c > index ad23cc8..435f6fa 100644 > --- a/drivers/char/hvc_dcc.c > +++ b/drivers/char/hvc_dcc.c > @@ -40,19 +40,6 @@ static inline u32 __dcc_getstatus(void) > } > > > -#if defined(CONFIG_CPU_V7) > -static inline char __dcc_getchar(void) > -{ > - char __c; > - > - asm volatile("get_wait: mrc p14, 0, pc, c0, c1, 0 \n\ > - bne get_wait \n\ > - mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" > - : "=r" (__c) : : "cc"); > - > - return __c; > -} > -#else > static inline char __dcc_getchar(void) > { > char __c; > @@ -62,24 +49,13 @@ static inline char __dcc_getchar(void) > > return __c; > } > -#endif > > -#if defined(CONFIG_CPU_V7) > -static inline void __dcc_putchar(char c) > -{ > - asm volatile("put_wait: mrc p14, 0, pc, c0, c1, 0 \n\ > - bcs put_wait \n\ > - mcr p14, 0, %0, c0, c5, 0 " > - : : "r" (c) : "cc"); > -} > -#else > static inline void __dcc_putchar(char c) > { > asm volatile("mcr p14, 0, %0, c0, c5, 0 @ write a char" > : /* no output register */ > : "r" (c)); > } > -#endif > > static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count) > { > -- > Sent by an employee of the Qualcomm Innovation Center, Inc. > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. >
WARNING: multiple messages have this Message-ID (diff)
From: nico@fluxnic.net (Nicolas Pitre) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Date: Mon, 20 Dec 2010 16:44:56 -0500 (EST) [thread overview] Message-ID: <alpine.LFD.2.00.1012201644110.10437@xanadu.home> (raw) In-Reply-To: <1292875718-7980-4-git-send-email-sboyd@codeaurora.org> On Mon, 20 Dec 2010, Stephen Boyd wrote: > The inline assembly differences for v6 vs. v7 in the hvc_dcc > driver are purely optimizations. On a v7 processor, an mrc with > the pc sets the condition codes to the 28-31 bits of the register > being read. It just so happens that the TX/RX full bits the DCC > driver is testing for are high enough in the register to be put > into the condition codes. On a v6 processor, this "feature" isn't > implemented and thus we have to do the usual read, mask, test > operations to check for TX/RX full. > > Since we already test the RX/TX full bits before calling > __dcc_getchar() and __dcc_putchar() we don't actually need to do > anything special for v7 over v6. The only difference is in > hvc_dcc_get_chars(). We would test RX full, poll RX full, and > then read a character from the buffer, whereas now we will test > RX full, read a character from the buffer, and then test RX full > again for the second iteration of the loop. It doesn't seem > possible for the buffer to go from full to empty between testing > the RX full and reading a character. Therefore, replace the v7 > versions with the v6 versions and everything works the same. > > 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> > --- > drivers/char/hvc_dcc.c | 24 ------------------------ > 1 files changed, 0 insertions(+), 24 deletions(-) > > diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c > index ad23cc8..435f6fa 100644 > --- a/drivers/char/hvc_dcc.c > +++ b/drivers/char/hvc_dcc.c > @@ -40,19 +40,6 @@ static inline u32 __dcc_getstatus(void) > } > > > -#if defined(CONFIG_CPU_V7) > -static inline char __dcc_getchar(void) > -{ > - char __c; > - > - asm volatile("get_wait: mrc p14, 0, pc, c0, c1, 0 \n\ > - bne get_wait \n\ > - mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" > - : "=r" (__c) : : "cc"); > - > - return __c; > -} > -#else > static inline char __dcc_getchar(void) > { > char __c; > @@ -62,24 +49,13 @@ static inline char __dcc_getchar(void) > > return __c; > } > -#endif > > -#if defined(CONFIG_CPU_V7) > -static inline void __dcc_putchar(char c) > -{ > - asm volatile("put_wait: mrc p14, 0, pc, c0, c1, 0 \n\ > - bcs put_wait \n\ > - mcr p14, 0, %0, c0, c5, 0 " > - : : "r" (c) : "cc"); > -} > -#else > static inline void __dcc_putchar(char c) > { > asm volatile("mcr p14, 0, %0, c0, c5, 0 @ write a char" > : /* no output register */ > : "r" (c)); > } > -#endif > > static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count) > { > -- > Sent by an employee of the Qualcomm Innovation Center, Inc. > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. >
next prev parent reply other threads:[~2010-12-20 21:44 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 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 [this message] 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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