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w1: mxc_w1: Optimize mxc_w1_ds2_touch_bit()

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According to the i.MX reference manual, the read/write bit operations
takes from 60 us to 120 us.
This patch optimizes mxc_w1_ds2_touch_bit() function to use proper
value for such delay. Nevertheless, a small margin for the timeout has
been added for the case if clock frequency is inaccurate.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alexander Shiyan 2014-05-08 11:56:40 +04:00 committed by Greg Kroah-Hartman
parent b7ce0b5d03
commit f80b2581a7
1 changed files with 15 additions and 12 deletions
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27
drivers/w1/masters/mxc_w1.c
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@ -75,22 +75,25 @@ static u8 mxc_w1_ds2_reset_bus(void *data)
*/
static u8 mxc_w1_ds2_touch_bit(void *data, u8 bit)
{
struct mxc_w1_device *mdev = data;
void __iomem *ctrl_addr = mdev->regs + MXC_W1_CONTROL;
unsigned int timeout_cnt = 400; /* Takes max. 120us according to
* datasheet.
*/
struct mxc_w1_device *dev = data;
unsigned long timeout;
writeb(MXC_W1_CONTROL_WR(bit), ctrl_addr);
writeb(MXC_W1_CONTROL_WR(bit), dev->regs + MXC_W1_CONTROL);
while (timeout_cnt--) {
if (!(readb(ctrl_addr) & MXC_W1_CONTROL_WR(bit)))
break;
/* Wait for read/write bit (60us, Max 120us), use 200us for sure */
timeout = jiffies + usecs_to_jiffies(200);
udelay(1);
}
udelay(60);
return !!(readb(ctrl_addr) & MXC_W1_CONTROL_RDST);
do {
u8 ctrl = readb(dev->regs + MXC_W1_CONTROL);
/* RDST bit is valid after the WR1/RD bit is self-cleared */
if (!(ctrl & MXC_W1_CONTROL_WR(bit)))
return !!(ctrl & MXC_W1_CONTROL_RDST);
} while (time_is_after_jiffies(timeout));
return 0;
}
static int mxc_w1_probe(struct platform_device *pdev)