path: root/Documentation/i2c
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authorJean Delvare <khali@linux-fr.org>2005-08-09 20:17:55 +0200
committerGreg Kroah-Hartman <gregkh@suse.de>2005-09-05 09:14:25 -0700
commita89ba0bc02e82920a0f4137aa5d655ac0366cc28 (patch)
tree98489ed77a287a81ff4ad7233fd543e59e58c328 /Documentation/i2c
parent3b6c0634cc989f0735a1541ccf9288947685cab5 (diff)
[PATCH] I2C: Rewrite i2c_probe
i2c_probe was quite complex and slow, so I rewrote it in a more efficient and hopefully clearer way. Note that this slightly changes the way the module parameters are handled. This shouldn't change anything for the most common cases though. For one thing, the function now respects the order of the parameters for address probing. It used to always do lower addresses first. The new approach gives the user more control. For another, ignore addresses don't overrule probe addresses anymore. This could have been restored the way it was at the cost of a few more lines of code, but I don't think it's worth it. Both lists are given as module parameters, so a user would be quite silly to specify the same addresses in both lists. The normal addresses list is the only one that isn't controlled by a module parameter, thus is the only one the user may reasonably want to remove an address from. Another significant change is the fact that i2c_probe() will no more stop when a detection function returns -ENODEV. Just because a driver found a chip it doesn't support isn't a valid reason to stop all probings for this one driver. This closes the long standing lm_sensors ticket #1807. http://www2.lm-sensors.nu/~lm78/readticket.cgi?ticket=1807 I updated the documentation accordingly. In terms of algorithmic complexity, the new code is way better. If I is the ignore address count, P the probe address count, N the normal address count and F the force address count, the old code was doing 128 * (F + I + P + N) iterations max, while the new code does F + P + ((I+1) * N) iterations max. For the most common case where F, I and P are empty, this is down from 128 * N to N. Signed-off-by: Jean Delvare <khali@linux-fr.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'Documentation/i2c')
1 files changed, 4 insertions, 3 deletions
diff --git a/Documentation/i2c/writing-clients b/Documentation/i2c/writing-clients
index 97e138cbb2a9..077275722a7c 100644
--- a/Documentation/i2c/writing-clients
+++ b/Documentation/i2c/writing-clients
@@ -241,9 +241,10 @@ Below, some things are only needed if this is a `sensors' driver. Those
parts are between /* SENSORS ONLY START */ and /* SENSORS ONLY END */
-This function should only return an error (any value != 0) if there is
-some reason why no more detection should be done anymore. If the
-detection just fails for this address, return 0.
+Returning an error different from -ENODEV in a detect function will cause
+the detection to stop: other addresses and adapters won't be scanned.
+This should only be done on fatal or internal errors, such as a memory
+shortage or i2c_attach_client failing.
For now, you can ignore the `flags' parameter. It is there for future use.