On 2017-01-08 11:51, Wolfram Sang wrote: > Hi peda, > >> One thing that I would like to do, but don't see a solution >> for, is to move the mux control code that is present in >> various drivers in drivers/i2c/muxes to this new minimalistic >> muxing subsystem, thus converting all present i2c muxes (but >> perhaps not gates and arbitrators) to be i2c-mux-simple muxes. > > In a few lines, what is preventing that? i2c-mux-gpio has the auto-detect for mux-/parent-locked and (old style?) support for specifying what gpios to use with platform data from code (i.e. not from dt/acpi). All of that gets messier if someone else (the mux) owns the gpios. i2c-mux-pinctrl has similar issues. i2c-mux-reg has the platform data from code issue, plus a read-write mode (mux is write only, at least as-is). i2c-mux-pca954x has things going on like irqs (not applied yet) and a reset gpio that makes it a poor candidate for something generic. i2c-mux-mlxcplc could probably be converted (I don't think it existed when I wrote the quoted paragraph). So, since there are issues with just about all of the i2c muxes, the only way forward that I see would be to instantiate the mux locally and feed it to the generic i2c-mux-simple, but what would be the point of that? There would still be a handful of i2c-mux drivers under drivers/i2c/muxes. Maybe some of the above are non-issues and maybe I have failed to see some issue? I didn't think too hard about it... >> I'm using an rwsem to lock a mux, but that isn't really a >> perfect fit. Is there a better locking primitive that I don't >> know about that fits better? I had a mutex at one point, but >> that didn't allow any concurrent accesses at all. At least >> the rwsem allows concurrent access as long as all users >> agree on the mux state, but I suspect that the rwsem will >> degrade to the mutex situation pretty quickly if there is >> any contention. > > Maybe ask this question in a seperate email thread on lkml cc-ing the > locking gurus (with a pointer to this thread)? I don't think there is a suitable primitive. In order to get something that really matches, I think the users need to hint how long they (think they) are going to lock the mux. And then it no longer a primitive, methinks. It something that is much heavier... >> Also, the "mux" name feels a bit ambitious, there are many muxes >> in the world, and this tiny bit of code is probably not good >> enough to be a nice fit for all... > > "... and it probably never will support anything other than > AT-harddisks, as that's all I have..." ;)) :-) > Thanks for this work! And thanks for looking! Cheers, peda -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
