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Date:   Thu, 06 May 2021 15:35:26 +0200
From:   Michael Walle <michael@walle.cc>
To:     Mark Brown <broonie@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Andy Shevchenko <andy.shevchenko@gmail.com>
Subject: Re: [PATCH 1/2] regmap: add regmap_might_sleep()
In-Reply-To: <20210506124342.GC4642@sirena.org.uk>
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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