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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

[akpm@linux-foundation.org: don't use kerenldoc token to introduce a non-kerneldoc comment, tweak whitespace]
Signed-off-by: Jean-Francois Dagenais <jeff.dagenais@gmail.com>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jean-Francois Dagenais 2013-07-03 15:09:15 -07:00 committed by Linus Torvalds
parent 5af1a9ce3d
commit d5528773e6
1 changed files with 30 additions and 0 deletions
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30
drivers/w1/slaves/w1_ds2408.c
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@ -302,7 +302,33 @@ static ssize_t w1_f29_write_status_control(
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 +389,10 @@ 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,