On Fri, May 05, 2023 at 04:56:47AM +0000, Vaittinen, Matti wrote: > On 5/4/23 17:33, Andy Shevchenko wrote: > > On Wed, May 03, 2023 at 12:50:14PM +0300, Matti Vaittinen wrote: ... > >> +config ROHM_BU27008 > >> + tristate "ROHM BU27008 color (RGB+C/IR) sensor" > >> + depends on I2C > >> + select REGMAP_I2C > >> + select IIO_GTS_HELPER > >> + help > >> + Enable support for the ROHM BU27008 color sensor. > >> + The ROHM BU27008 is a sensor with 5 photodiodes (red, green, > >> + blue, clear and IR) with four configurable channels. Red and > >> + green being always available and two out of the rest three > >> + (blue, clear, IR) can be selected to be simultaneously measured. > >> + Typical application is adjusting LCD backlight of TVs, > >> + mobile phones and tablet PCs. > > > > Module name? > > We have discussed this several times already. > > https://lore.kernel.org/all/10c4663b-dd65-a545-786d-10aed6e6e5e9@xxxxxxxxxxxxxxxxx/ > > Module name is completely irrelevant when selecting a kernel configuration. This option is also selectable by user. ... > > Do you need regmap lock? If so, why (since you have mutex)? > > I believe you know that regmap uses a default lock when no external lock > is given. So, I assume you mean that maybe we could set > 'disable_locking' for the regmap here. Correct. > It's nice to be occasionally pushed to think "out of the box". And yes, > disabling regmap lock is really out of my "normal box" :) > > I didn't go through all of the code yet, but I think pretty much all of > the sequences which end up to register writes are indeed protected by > the mutex. (Well, probe is not but it is expected to only update one bit > while rest of the register should stay fixed). > > It may be we could live without regmap_lock when driver is in it's > current state, but I am not convinced the performance improvement is > worth the risk. Having regmap unprotected is not common, and it is also > not easy to spot when making changes to the driver. In my opinion it is > a bit like asking for a nose-bleed unless there is really heavy reasons > to drop the lock... In this case, having the regmap_lock (which is > pretty much never locked because we have the mutex as you said) is > probably not a penalty that matters. Basically you try to justify a hidden mine field in case somebody will think "oh, we are protected by regmap lock, so why to bother call mutex_lock()" and at the end it become a subtle bugs in the code. With disable_locking = true I can see that code author _carefully thought through_ the locking schema and understands the hardware and the code. P.S. I'm wondering why your lines of text have a single trailing whitespace but the last line. -- With Best Regards, Andy Shevchenko
