From: Mariusz Bialonczyk manio@skyboo.net
[ Upstream commit 62909da8aca048ecf9fbd7e484e5100608f40a63 ]
From the DS2408 datasheet [1]:
"Resume Command function checks the status of the RC flag and, if it is set, directly transfers control to the control functions, similar to a Skip ROM command. The only way to set the RC flag is through successfully executing the Match ROM, Search ROM, Conditional Search ROM, or Overdrive-Match ROM command"
The function currently works perfectly fine in a multidrop bus, but when we have only a single slave connected, then only a Skip ROM is used and Match ROM is not called at all. This is leading to problems e.g. with single one DS2408 connected, as the Resume Command is not working properly and the device is responding with failing results after the Resume Command.
This commit is fixing this by using a Skip ROM instead in those cases. The bandwidth / performance advantage is exactly the same.
Refs: [1] https://datasheets.maximintegrated.com/en/ds/DS2408.pdf
Signed-off-by: Mariusz Bialonczyk manio@skyboo.net Reviewed-by: Jean-Francois Dagenais jeff.dagenais@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/w1/w1_io.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/w1/w1_io.c b/drivers/w1/w1_io.c index 0364d3329c526..3516ce6718d94 100644 --- a/drivers/w1/w1_io.c +++ b/drivers/w1/w1_io.c @@ -432,8 +432,7 @@ int w1_reset_resume_command(struct w1_master *dev) if (w1_reset_bus(dev)) return -1;
- /* This will make only the last matched slave perform a skip ROM. */ - w1_write_8(dev, W1_RESUME_CMD); + w1_write_8(dev, dev->slave_count > 1 ? W1_RESUME_CMD : W1_SKIP_ROM); return 0; } EXPORT_SYMBOL_GPL(w1_reset_resume_command);