Re: [PATCH 1/2] regmap: add regmap_might_sleep()

[Michael Walle]

Am 2021-05-06 14:43, schrieb Mark Brown:
> On Sat, May 01, 2021 at 12:10:16AM +0200, Michael Walle wrote:
> > Am 2021-04-30 19:26, schrieb Mark Brown:
>
> > > But that's a driver for a specific device AFAICT which looks like it's
> > > only got an I2C binding on the MFD so the driver knows that it's for a
> > > device that's on a bus that's going to sleep and doesn't need to infer
> > > anything?  This looks like the common case I'd expect where there's no
> > > variation.
>
> > You are right, at the moment this driver only has an I2C binding. But
> > the idea was that this IP block and driver can be reused behind any
> > kind of bridge; I2C, SPI or MMIO. Actually, I had the impression
>
> Is this actually a way people are building hardware though?

Granted, this might be a special case because the driver is for an
IP inside CPLD/FPGA, thus you could easily switch the bridge.

> > that all you need to do to convert it to MMIO is to replace the
> > "kontron,sl28cpld" compatible with a "syscon" compatible. But it isn't
> > that easy. Anyway, the idea is that you don't need to change anything
> > in the gpio-sl28cpld driver, just change the parent. But if we can't
> > ask the regmap what type it is, then we'll have to modify the
> > gpio-sl28cpld driver and we will have to figure it out by some other
> > means.
>
> Well, you don't need to change anything at all - the driver will work
> perfectly fine if it's flagging up the GPIOs as potentially sleeping
> even if they end up not actually sleeping.

Unless you need the non-sleeping version for a gpio.

> > > If users happen to end up with a map flagged as fast they can work on
> > > the whatever driver uses this stuff and not realise they're breaking
> > > other users of the same driver that end up with slow I/O.  The whole
> > > point of the flag in GPIO is AIUI warnings to help with that case.
>
> > Hm, but as of now, the only thing which makes the gpio-regmap driver
> > slow i/o is the regmap itself.
>
> Surely it's just a case of the device that's creating the gpio regmap
> setting a flag when it instantiates it?  It's just one more thing that
> the parent knows about the device.  This doesn't seem insurmountable.

No its not. It just seemed like it is way easier to just ask the regmap.

-michael