On Wed, 2021-05-26 at 12:27 +0200, Michael Walle wrote:

Am 2021-05-26 11:44, schrieb Matti Vaittinen:

quoted

On Wed, 2021-05-26 at 11:07 +0200, Michael Walle wrote:

quoted

Am 2021-05-26 10:42, schrieb Andy Shevchenko:

quoted

On Wed, May 26, 2021 at 9:02 AM Matti Vaittinen
[off-list ref] wrote:

quoted

Support providing some IC specific operations at gpio_regmap
registration.

Implementation of few GPIO related functionalities are likely
to
be
very IC specific. For example the pin-configuration registers
and
the
pin validity checks. Allow IC driver to provide IC specific
functions
which gpio-regmap can utilize for these IC specific
configurations.
This should help broaden the gpio-regmap IC coverage without
the
need
of exposing the registered gpio_chip or struct gpio_regmap to
IC
drivers.

The set_config and init_valid_mask are used by ROHM BD71815
GPIO
driver.
Convert the BD71815 GPIO driver to use gpio-regmap and get
rid of
some
code. Rest of the ROHM GPIO drivers are to be reworked after
the
mechanism of adding IC specific functions is settled.

Some preliminary discussion can be seen here:
https://lore.kernel.org/linux-gpio/c4faac648d3e0c7f3dcb50f7e24c8b322e8c6974.camel@fi.rohmeurope.com/ (local)

I did also prepare change where the getters for drvdata and
regmap
are used. It can also work - but it does not scale quite as
well
if (when) IC drivers need some register information to do
custom
operations. Interested people can see the:
https://github.com/M-Vaittinen/linux/commits/gpio-regmap-getters
for comparison.

Entire series looks good to me,

Sorry, for being late to this. I got sidetracked.

TBH, I don't like the we have the config struct in the callbacks.
Why
would you need all this information in the callback?

I believe there will be cases when the register information is
needed
in callbacks. I don't know the GPIO controllers in details so that
I
could give you an real-word example. I guess other people on the
list
know the usual GPIO quirks far better than I do. I however have
seen
bunch of hardware - and usually each IC has _some_ strange stuff. I
would be surprized if there weren't any cases where the one
operation
"toggle X" would not require access to another register which is
used
to control "feature Y" - and usually only once in a blue moon.
Purely
imaginatory example could be that in order to change direction to
input, one would need to ensure some bit in a output configuration
register is cleared. Then it would be beneficial to have the
register
description in call-back.

Doing something depening on the offsets of some registers sounds like
a hack to me.

Hm. I an unsure I understood your comment. If the hardware requires
setting a bit - then we must do it using the bit offset. What we win
here is that we can get the register address from config w/o allocating
driver data.

quoted

Or, if we look at the pinctrl-bcm63xx.c - another imaginatory case
- we
would get another HW variant with different BCM63XX_BANK_GPIOS
value.
Now the IC would not need to store the correct BCM63XX_BANK_GPIOS
in
driver data for the xlate-callback - it could directly read the
ngpio_per_reg from config.

which also sounds like a hack, where one really should provide a
driver priv to distiguish between different variant.

I disagree here. Storing a IC type flag in private data does not scale
well when we have many variants and many 'entities' that depend on the
variant. If we just have the IC type passed to call-back, then the
call-back must have all variant details hard-coded. It scales better if
we can just provide the correct value for the variant - not the variant
type.

quoted

As I said, these cases are imaginatory - I don't know the GPIO
controllers well enough to give real-world examples - but I am
positive
there are such.

quoted

 And it doesn't
help you to call back into gpio-regmap once there are further
methods
provided by gpio-regmap.

If we later need this we can use container_of(), right?

Of course, but isn't your argument to have less boilerplate? ;)

Yes. We can provide the function "gpio_regmap_get_from_config()" which
returns the pointer to struct gpio_regmap - _if ever needed_ instead of
providing bunch of getter functions. (That would be driver_data, regmap
and firmware node already now just to fulfill the needs to the bd71815
- which probably is one of the simplest controllers). So one
potentially needed function vs three that would be needed already now.

 And
again, I don't thing the config is the correct first parameter here
for the callback. And it would be different from all the other
subsystems in linux (as far as I know, please correct me if I'm
wrong),
which have "their" (sometimes opaque, sometimes not) pointer as the
first argument.

I only know handful of subsystems - and most of those expose the
internals. That's why I suggested it at first. Andy and you both
thought exposing the gpio_regmap or gpio_chip to gpio_regmap users was
a bad idea - hence I suggested this solution - which actually looks
good to me :)

quoted

quoted

Either we hide away the internals completely (which I still
prefer!)
or
we open up the gpio_regmap struct. But this is somewhere in
between.

Yes. And I think this is the simplest and cleanest solution which
still
provides decent amount of protection, while cuts off the
boilerplate.

I really don't find this solution "clean".

quoted

Additionally this does not add any extra structures because IC
drivers
already know the config. Some gpio_regmap internals (like
gpio_chip)
can still be kept internal - while config (which in any case is
populated by the IC driver) is public.

quoted

As
the user, you could already attach the config to the opaque data
pointer
and get the same result.

Actually no. This would require user to permanently store the
config in
memory which would either duplicate the config or give IC driver a
pointer to gpio_regmap internals. This solution still gives pointer
to
gpio_regmap config - but at least we can set it const in function
parameters.

Of course, your caller has to make sure it will allocate the memory
and doesn't just allocate it on the stack. You're doing the same,
just in gpio-regmap.

Point was that this way we are not necessarily permanently allocating
the memory both in the gpio_regmap _and_ the IC driver. We are also not
allowing IC driver to change config stored in gpio_regmap (well,
without some tricks anyways).

quoted

quoted

I don't see how the following is an overhead:

int gpio_regmap_callback(struct gpio_regmap *gpio, ..)
{
     struct regmap *regmap = gpio_regmap_get_regmap(gpio);
     struct driver_priv *data = gpio_regmap_get_drvdata(gpio);
     ...
}
It doesn't clutter anything, there is just a small runtime
overhead
(is
it?). Again this let you keep adding stuff in the future without
changing any users. So what are the drawbacks of this?

It still is overhead. Additionally, I dislike mixing function calls
with declarations - I know that's probably just my personal
preference
though.

Well yes, thats just a matter of taste. Everyone is doing
platform_get_drvdata(), for example. If you want to keep something
internal you'd need accessor methods.

quoted

And what is not shown here is the need to declare, define and
export these functions from gpio_regmap. And this is really just
unnecessary boilerplate to me.

Exporting the functions is just adding two lines in gpio/regmap.h.
How 
can
this be an argument for an overhead on the users?

quoted

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Also I'd like to keep the duplication of the "struct gpio_regmap"
members
and the config members. The gpio_regmap_config is just a struct
so
the _register won't get cluttered with arguments.

The config (as passed from IC driver at register) is dublication.
We
do:
gpio->config = *config;

Yes and I actually had that during my initial development, but
decided
against it, to decouple the information you'll need later and some
you might just discard after probe.

I'm afraid, but I really don't like having the gpio_regmap_config as
the first parameter on callbacks, just because I think this is the
wrong approach, so I vote against this change. I guess it is up
to Linus to decide on this.

Don't get me wrong, I'm all open for change, but there seems to be
two
equal approaches to your problem, which just depends on personal
taste.

No problem Michael - we are all allowed to have our own opinions - even
the wrong ones ;) Nah, really, the discussion is good. It rarely hurts
the outcome. I think I've explained my view now too. Let's see what
other think :)

Best Regards
	Matti Vaittinen


--
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~

Simon says - in Latin please.
"non cogito me" dixit Rene Descarte, deinde evanescavit

(Thanks for the translation Simon)


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