[RFC] w1: regression, remove need for ida and use PLATFORM_DEVID_AUTO

[Andrew F. Davis]

On 02/02/2017 07:31 PM, Petr Cvek wrote:
> Dne 2.2.2017 v 15:23 Andrew F. Davis napsal(a):
>> On 02/01/2017 07:05 PM, Petr Cvek wrote:
>>> Patch 
>>> 	w1: remove need for ida and use PLATFORM_DEVID_AUTO
>>> 	098f9fb0c962eb2fdba5f9d34f4cf7a938237184 
>>>
>>> causes a regression in the w1_ds2760 driver. Initialization creates a name "ds2760-battery.0.auto". It seems that name of that size will cause checking code in __thermal_cooling_device_register() from thermal_core.c to fail as it checks for names shorter than 20 chars:
>>>
>>> 	if (type && strlen(type) >= THERMAL_NAME_LENGTH)
>>> 		return ERR_PTR(-EINVAL);
>>>
>>> A second problem seems to be with magician_supplicants list as "ds2760-battery.0" does not match in a test power_supply_am_i_supplied() in ds2760_battery_update_status() from drivers/power/supply/ds2760_battery.c . This causes status flag to be forever in POWER_SUPPLY_STATUS_DISCHARGING state.
>>>
>>> Functionality returned after I hotfix changed (drivers/w1/slaves/w1_ds2760.c)
>>>
>>> 	pdev = platform_device_alloc("ds2760-battery", PLATFORM_DEVID_AUTO);
>>>
>>> to
>>>
>>> 	pdev = platform_device_alloc("ds2760-battery", 0);
>>>
>>> Which solution do you advise. Shortening the name let's say just to "ds2760" (with changes to arch files, w1 files and supply files), increasing THERMAL_NAME_LENGTH to let's say 32 (I don't know if this doesn't break something other) or just reverting to the old behavior?
>>>
>>
>> If 20 is no longer the max thermal name then THERMAL_NAME_LENGTH should
>> be changed.
> 
> Yes it is that ".auto" addition to "ds2760-battery.0" makes 21 chars long string. With higher number (".10" onwards) it is 22 chars. Load of the module then fails at test in thermal_zone_device_register():
> 
> 	https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/thermal/thermal_core.c?id=refs/tags/v4.10-rc6#n1158
> 
> 	if (type && strlen(type) >= THERMAL_NAME_LENGTH)
> 		return ERR_PTR(-EINVAL);
> 
> I searched in code further and with THERMAL_NAME_LENGTH = 30 (enough space) the module load fails at another place in __hwmon_device_register():
> 	
> 	https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/hwmon/hwmon.c?id=refs/tags/v4.10-rc6#n548
> 
> 	if (name && (!strlen(name) || strpbrk(name, "-* \t\n")))
> 		return ERR_PTR(-EINVAL);
> 
> That's because there is "-" in "ds2760-battery.0.auto" (and that's why shortening to "ds2760.0" works). Is there some reason for disallowing "-" in a name? If not then I'm for removal (in other case we need to change ds2760-battery and others names). Increasing THERMAL_NAME_LENGTH to 22 should be just OK for ds2760 (but maybe not enough for others) I would increased it to 32 (nice number ;-) ).
> 
>>
>> As for the couple boards hard-coding "ds2760-battery.0", this is a
>> problem that should be fix regardless of any fix we chose here as IDA is
>> not guaranteed to return 0, so the battery could just as easily be
>> called ds2760-battery.7. (I've had this discussion before as the N900
>> user-space also make this mistake).
>>
> 
> I'm not familiar with power supply subsystem, so just a naive idea. Should suffice to change drivers/power/supply/power_supply_core.c __power_supply_is_supplied_by() for only first part of the string? (like "ds2760-battery" subset of "ds2760-battery.7").
> 
> Do you have a link to discussion about N900?
> 

The thread doesn't look to have happened on the lists, but the commit
that reverted my change is: 9aafabc7fece. I argued against this revert
as relying on sysfs names never changing should be considered ABI abuse
and we should not hold back proper fixes for the sake of keeping a hack
in user-space working.

Andrew

> Petr
>