Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751478Ab0LRFQb (ORCPT ); Sat, 18 Dec 2010 00:16:31 -0500 Received: from wolverine01.qualcomm.com ([199.106.114.254]:10338 "EHLO wolverine01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751179Ab0LRFQ2 (ORCPT ); Sat, 18 Dec 2010 00:16:28 -0500 X-IronPort-AV: E=McAfee;i="5400,1158,6200"; a="67336980" From: Stephen Boyd To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Tony Lindgren , Arnd Bergmann , Nicolas Pitre , Daniel Walker Subject: [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM Date: Fri, 17 Dec 2010 21:16:25 -0800 Message-Id: <1292649385-28771-1-git-send-email-sboyd@codeaurora.org> X-Mailer: git-send-email 1.7.3.4.516.g15368e In-Reply-To: <20101201192856.GA731@suse.de> References: <20101201192856.GA731@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4120 Lines: 133 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. While we're here, cleanup the for loops a bit and mark the inline assembly as volatile. Not marking it volatile causes GCC to cache the results of the status and RX buffer registers causing lockups. Cc: Tony Lindgren Cc: Arnd Bergmann Cc: Nicolas Pitre Cc: Daniel Walker Signed-off-by: Stephen Boyd --- drivers/char/hvc_dcc.c | 43 +++++++------------------------------------ 1 files changed, 7 insertions(+), 36 deletions(-) diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c index 6470f63..435f6fa 100644 --- a/drivers/char/hvc_dcc.c +++ b/drivers/char/hvc_dcc.c @@ -33,54 +33,29 @@ static inline u32 __dcc_getstatus(void) { u32 __ret; - - asm("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg" + asm volatile("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg" : "=r" (__ret) : : "cc"); return __ret; } -#if defined(CONFIG_CPU_V7) static inline char __dcc_getchar(void) { char __c; - asm("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; - - asm("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" + asm volatile("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" : "=r" (__c)); return __c; } -#endif -#if defined(CONFIG_CPU_V7) -static inline void __dcc_putchar(char c) -{ - asm("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("mcr p14, 0, %0, c0, c5, 0 @ write a char" + 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) { @@ -90,7 +65,7 @@ static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count) while (__dcc_getstatus() & DCC_STATUS_TX) cpu_relax(); - __dcc_putchar((char)(buf[i] & 0xFF)); + __dcc_putchar(buf[i]); } return count; @@ -100,15 +75,11 @@ static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count) { int i; - for (i = 0; i < count; ++i) { - int c = -1; - + for (i = 0; i < count; ++i) if (__dcc_getstatus() & DCC_STATUS_RX) - c = __dcc_getchar(); - if (c < 0) + buf[i] = __dcc_getchar(); + else break; - buf[i] = c; - } return i; } -- 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/