On 2021-10-05 15:03:49, Daniel Thompson wrote: [..]
I much prefer doing that instead of trying to wrangle enumeration parsing around integer values that are supposed to be used as-is. After all this variable is already named to set the `+ 1` override currently, and `qcom,enabled_strings` has "custom" handling as well. I'll extend the validation to ensure num_strings>=1 too.
Great.
In addition, and this needs some investigation on the dt-bindings side too, it might be beneficial to make both properties mutually exclusive. When specifying qcom,enabled_strings it makes little sense to also provide qcom,num_strings and we want the former to take precedence.
If we are designing a "fix" for that then my view is that if both are passed then num-strings should take precedence because it is an explicit statement about the number of strings where enabled_strings is implicit. In other words, if num-strings <= len(enabled_strings) then we should do what we are told, otherwise report error.
IMO both should be identical (num-strings == len(enabled-strings)) to avoid ambiguity, but do read on.
At that point one might ask why qcom,num_strings remains at all when DT can use qcom,enabled_strings instead. We will supposedly have to keep backwards compatibility with DTs in mind so none of this can be removed or made mutually exclusive from a driver standpoint, that all has to be done in dt-bindings yaml to be enforced on checked-in DTs.
So... perhaps I made a make offering a Reviewed-by: to a patch that allows len(enabled-strings) to have precedence. If anything currently uses enabled-strings then it *will* be 4 cells long and is relying on num-strings to ensure the right things happens ;-) .
Unfortunately Konrad (one of my team members) landed such a patch at the beginning of this year because I failed to submit this patchset in time while it has been sitting in my queue since 2019 after being used in a downstream project. This is in pmi8994 which doesn't have anything widely used / production ready yet, so I'd prefer to fix the DT instead and remove / fix his comment:
/* Yes, all four strings *have to* be defined or things won't work. */
But this is mostly because, prior to this patchset, no default was set for WLED4 so the 0'th string would get enabled num-strings (3 in pmi8994's case) times.
Aside that there's only one more PMIC (also being worked on by SoMainline) that sets qcom,enabled-strings: this is pm660l, pulled from our local tree, and it actually has enabled-strings of length 2 which is broken in its current form, exactly because of relying on this patchset.
Finally, we already discussed this inside SoMainline and the number/enabled leds should most likely be moved out of the PMIC dtsi's as they're probably panel, hence board or even device dependent.
We'd like that case to keep working so we must allow num-strings to have precedence. In other words, when you add the new code, please put it at the end of the function!
Since there don't seem to be any substantial platforms/PMICs using this functionality in a working manner, can I talk you into agreeing with fixing the DT instead?
PS. In -next pmi8994_wled is only enabled for sony-xperia-tone, and pm660l_wled has yet to be enabled by anything.
- Marijn