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authorJean-Francois Dagenais <jeff.dagenais@gmail.com>2013-07-03 15:09:15 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-07-03 16:08:06 -0700
commitd5528773e68e35512f69dd574e25d8c81e7d3105 (patch)
tree303e9e88c3f97edd17f625b0f88562967e70491b /drivers/w1
parent5af1a9ce3d114bbd49b5a06bfc5f5404d73709e3 (diff)
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>
Diffstat (limited to 'drivers/w1')
-rw-r--r--drivers/w1/slaves/w1_ds2408.c30
1 files changed, 30 insertions, 0 deletions
diff --git a/drivers/w1/slaves/w1_ds2408.c b/drivers/w1/slaves/w1_ds2408.c
index 91cc2cdf02c..cb8a8e5d957 100644
--- a/drivers/w1/slaves/w1_ds2408.c
+++ b/drivers/w1/slaves/w1_ds2408.c
@@ -302,7 +302,33 @@ 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 +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,