From f1f629d926b8189d98af532b57933595e85c055b Mon Sep 17 00:00:00 2001 From: Jean-Francois Dagenais Date: Fri, 28 Jun 2013 09:54:14 +1000 Subject: [PATCH] drivers/w1/slaves/w1_ds2408.c: add magic sequence to disable P0 test mode Power-up timing The DS2408 is sensitive to the power-on slew rate and can inadvertently power up with a test mode feature enabled. When this occurs, the P0 port does not respond to the Channel Access Write command. For most reliable operation, it is recommended to disable the test mode after every power-on reset using the Disable Test Mode sequence shown below. The 64-bit ROM code must be transmitted in the same bit sequence as with the Match ROM command, i.e., least significant bit first. This precaution is recommended in parasite power mode (VCC pin connected to GND) as well as with VCC power. Disable Test Mode: RST,PD,96h,<64-bit DS2408 ROM Code>,3Ch,RST,PD Signed-off-by: Jean-Francois Dagenais Cc: Evgeniy Polyakov Cc: Greg KH Signed-off-by: Andrew Morton --- drivers/w1/slaves/w1_ds2408.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/drivers/w1/slaves/w1_ds2408.c b/drivers/w1/slaves/w1_ds2408.c index 91cc2cdf02c0..01fe4483778f 100644 --- a/drivers/w1/slaves/w1_ds2408.c +++ b/drivers/w1/slaves/w1_ds2408.c @@ -302,7 +302,32 @@ error: return -EIO; } +/** + * This is a special sequence we must do to ensure the P0 output is not stuck + * in test mode. This is described in rev 2 of the ds2408's datasheet + * (http://datasheets.maximintegrated.com/en/ds/DS2408.pdf) under + * "APPLICATION INFORMATION/Power-up timing". + */ +static int w1_f29_disable_test_mode(struct w1_slave *sl) +{ + int res; + u8 magic[10] = {0x96, }; + u64 rn = le64_to_cpu(*((u64*)&sl->reg_num)); + memcpy(&magic[1], &rn, 8); + magic[9] = 0x3C; + + mutex_lock(&sl->master->bus_mutex); + res = w1_reset_bus(sl->master); + if (res) + goto out; + w1_write_block(sl->master, magic, ARRAY_SIZE(magic)); + + res = w1_reset_bus(sl->master); +out: + mutex_unlock(&sl->master->bus_mutex); + return res; +} static struct bin_attribute w1_f29_sysfs_bin_files[] = { { @@ -363,6 +388,10 @@ static int w1_f29_add_slave(struct w1_slave *sl) int err = 0; int i; + err = w1_f29_disable_test_mode(sl); + if (err) + return err; + for (i = 0; i < ARRAY_SIZE(w1_f29_sysfs_bin_files) && !err; ++i) err = sysfs_create_bin_file( &sl->dev.kobj, -- 2.39.5