| From d25b69e697be7de1e4beaebf27dc08c1ca71ac68 Mon Sep 17 00:00:00 2001 |
| From: Mariusz Bialonczyk <manio@skyboo.net> |
| Date: Thu, 21 Mar 2019 11:52:55 +0100 |
| Subject: w1: fix the resume command API |
| |
| [ 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); |
| -- |
| 2.20.1 |
| |