Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757349Ab0LTVo6 (ORCPT ); Mon, 20 Dec 2010 16:44:58 -0500 Received: from relais.videotron.ca ([24.201.245.36]:16817 "EHLO relais.videotron.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754179Ab0LTVo5 (ORCPT ); Mon, 20 Dec 2010 16:44:57 -0500 MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: TEXT/PLAIN; charset=US-ASCII Date: Mon, 20 Dec 2010 16:44:56 -0500 (EST) From: Nicolas Pitre X-X-Sender: nico@xanadu.home To: Stephen Boyd Cc: Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Tony Lindgren , Arnd Bergmann , Daniel Walker Subject: Re: [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM In-reply-to: <1292875718-7980-4-git-send-email-sboyd@codeaurora.org> Message-id: References: <1292649385-28771-1-git-send-email-sboyd@codeaurora.org> <1292875718-7980-1-git-send-email-sboyd@codeaurora.org> <1292875718-7980-4-git-send-email-sboyd@codeaurora.org> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3258 Lines: 92 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 > Cc: Arnd Bergmann > Cc: Nicolas Pitre > Cc: Daniel Walker > Signed-off-by: Stephen Boyd Acked-by: Nicolas Pitre > --- > 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. > -- 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/