From b0dceb6a96c2f87a40a9f99bc05711a3f7c1eaa2 Mon Sep 17 00:00:00 2001 From: Alexander Shiyan Date: Thu, 8 May 2014 11:56:38 +0400 Subject: w1: mxc_w1: Optimize mxc_w1_ds2_reset_bus() According to the i.MX reference manual, the reset procedure and "presence" pulse takes 511 and 512 us, respectively. Measurement for i.MX27 is about 1100 us. There is no need to wait Reset+Presence more than this time. This patch optimizes mxc_w1_ds2_reset_bus() function to use proper value for delay after w1 bus reset. Nevertheless, a small margin for the timeout has been added for the case if clock frequency is inaccurate. Signed-off-by: Alexander Shiyan Signed-off-by: Greg Kroah-Hartman --- drivers/w1/masters/mxc_w1.c | 32 +++++++++++++++----------------- 1 file changed, 15 insertions(+), 17 deletions(-) (limited to 'drivers') diff --git a/drivers/w1/masters/mxc_w1.c b/drivers/w1/masters/mxc_w1.c index a5df5e89d456..0d05abe34362 100644 --- a/drivers/w1/masters/mxc_w1.c +++ b/drivers/w1/masters/mxc_w1.c @@ -15,16 +15,13 @@ #include #include #include +#include #include #include #include "../w1.h" #include "../w1_int.h" -/* According to the mx27 Datasheet the reset procedure should take up to about - * 1350us. We set the timeout to 500*100us = 50ms for sure */ -#define MXC_W1_RESET_TIMEOUT 500 - /* * MXC W1 Register offsets */ @@ -49,24 +46,25 @@ struct mxc_w1_device { */ static u8 mxc_w1_ds2_reset_bus(void *data) { - u8 reg_val; - unsigned int timeout_cnt = 0; struct mxc_w1_device *dev = data; + unsigned long timeout; - writeb(MXC_W1_CONTROL_RPP, (dev->regs + MXC_W1_CONTROL)); + writeb(MXC_W1_CONTROL_RPP, dev->regs + MXC_W1_CONTROL); - while (1) { - reg_val = readb(dev->regs + MXC_W1_CONTROL); + /* Wait for reset sequence 511+512us, use 1500us for sure */ + timeout = jiffies + usecs_to_jiffies(1500); - if (!(reg_val & MXC_W1_CONTROL_RPP) || - timeout_cnt > MXC_W1_RESET_TIMEOUT) - break; - else - timeout_cnt++; + udelay(511 + 512); - udelay(100); - } - return !(reg_val & MXC_W1_CONTROL_PST); + do { + u8 ctrl = readb(dev->regs + MXC_W1_CONTROL); + + /* PST bit is valid after the RPP bit is self-cleared */ + if (!(ctrl & MXC_W1_CONTROL_RPP)) + return !(ctrl & MXC_W1_CONTROL_PST); + } while (time_is_after_jiffies(timeout)); + + return 1; } /* -- cgit v1.2.3