On 4/3/24 4:30 PM, Guenter Roeck wrote:
On Wed, Apr 03, 2024 at 03:36:02PM -0500, Andrew Davis wrote:
Hello all,
Goal here is to remove the i2c_match_id() function from all drivers.
Using i2c_get_match_data() can simplify code and has some other
benefits described in the patches.
The return value from i2c_match_id() is typically an integer (chip ID)
starting with 0. Previously it has been claimed that this would be
unacceptable for i2c_get_match_data(), and chip IDs were changed to start
with 1. Commit ac0c26bae662 ("hwmon: (lm25066) Use i2c_get_match_data()")
is an example. Either this series is wrong, or the previous claim that
chip IDs (i.e., the content of .driver_data or .data) must not be 0 was
wrong. Which one is it ? I find it very confusing that the chip type for
some drivers now starts with 1 and for others with 0. Given that, I am not
inclined to accept this series unless it is explained in detail why the
chip type enum in, for example, drivers/hwmon/pmbus/lm25066.c has to start
with one but is ok to start with 0 for all drivers affected by this
series. Quite frankly, even if there is some kind of explanation, I am not
sure if I am going to accept it because future driver developers won't
know if they have to start chip types with 0 or 1.
i2c_get_match_data() has no issue with returning 0 when the driver_data
for the match is also 0 (as it will be when the chip type is 0 here).
The confusion might be that returning 0 is also considered a failure code.
This is a problem in general with returning errors in-band with data, and
that is nothing new as i2c_match_id() does the same thing.
Actually, i2c_match_id() is worse as most of these drivers take the result
from that and immediately dereference it. Meaning if i2c_match_id() ever did
failed to find a match, they would crash before this series. Luckily i2c_match_id()
can't fail to find a match as far as I can tell, and so for the same reason
neither can i2c_get_match_data(), which means if 0 is returned it is always
because the chip ID was actually 0.
At some point we should switch all the *_get_match_data() functions to
return an error code and put the match if found as a argument pointer.
Forcing everyone to changing the chip type to avoid 0 as done in
ac0c26bae662 is the wrong way to fix an issue like that.
Andrew
