On 02/08/2019 00:42, Mark Brown wrote: > On Tue, Jul 30, 2019 at 05:28:11PM +0100, Thomas Preston wrote: >> On 30/07/2019 16:50, Mark Brown wrote: > >>> Like I say it's not just debugfs though, there's the standard driver >>> interface too. > >> Ah right, I understand. So if we run the turn-on diagnostics routine, there's >> nothing stopping anyone from interacting with the device in other ways. > >> I guess there's no way to share that mutex with ALSA? In that case, it doesn't >> matter if this mutex is there or not - this feature is incompatible. How >> compatible do debugfs interfaces have to be? I was under the impression anything >> goes. I would argue that the debugfs is better off for having the mutex so >> that no one re-reads "diagnostic" within the 5s poll timeout. > > It's not really something that's supported; like Charles says the DAPM > mutex is exposed but if the regular controls would still be able to do > stuff. It is kind of a "you broke it, you fix it" thing but on the > other hand it's better to make things safer if we can since it might not > be obvious later on why things are broken. > >> Alternatively, this diagnostic feature could be handled with an external-handler >> kcontrol SOC_SINGLE_EXT? I'm not sure if this is an atomic interface either. >> >> What would be acceptable? > > Yes, that's definitely doable - we've got some other drivers with > similar things like calibration triggers exposed that way. > One problem with using a kcontrol as a trigger for the turn-on diagnostic is that the diagnostic routine has a "return value". It goes like this: - Bring device to low-quiescent state - Initiate diagnostics - Poll for diagnostics-complete bit - Read the four channel status registers The final read clears the status registers, so this isn't something I can just do with regmap. One idea I had was to initiate the turn-on diagnostics using a kcontrol, whose handler saves the four channel status registers and an epoch in tda7802_priv. Then this can be read from debugfs. But it seems strange to have to turn on this control over here, then go over there and read this value. Hm, maybe a better idea is to have the turn on diagnostic only run on device probe (as its name suggests!), and print something to dmesg: modprobe tda7802 turn_on_diagnostic=1 tda7802-codec i2c-TDA7802:00: Turn on diagnostic 04 04 04 04 Kirill Marinushkin mentioned this in the first review [0], it just didn't really sink in until now! [0] https://lkml.org/lkml/2019/6/14/1344
