linux-kernel - Re: [PATCH v2 1/3] gpio: regmap: Support few IC specific operations

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Message-ID: <26eb6b95805840dca05e0135e0555b42@walle.cc>
Date:   Fri, 21 May 2021 12:46:29 +0200
From:   Michael Walle <michael@...le.cc>
To:     "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
Cc:     andy.shevchenko@...il.com,
        linux-power <linux-power@...rohmeurope.com>,
        linux-gpio@...r.kernel.org, bgolaszewski@...libre.com,
        linux-kernel@...r.kernel.org, linus.walleij@...aro.org
Subject: Re: [PATCH v2 1/3] gpio: regmap: Support few IC specific operations

Am 2021-05-21 12:25, schrieb Vaittinen, Matti:
> On Fri, 2021-05-21 at 12:19 +0200, Michael Walle wrote:
>> Am 2021-05-21 12:09, schrieb Andy Shevchenko:
>> > On Fri, May 21, 2021 at 12:53 PM Matti Vaittinen
>> > <matti.vaittinen@...rohmeurope.com> wrote:
>> > > Changelog v2: (based on suggestions by Michael Walle)
>> > >   - drop gpio_regmap_set_drvdata()
>> >
>> > But why do we have gpio_regmap_get_drvdata() and why is it
>> > different
>> > now to the new member handling?
>> 
>> Eg. the reg_mask_xlate() callback is just passed a "struct
>> gpio_regmap*".
>> If someone needs to access private data there,
>> gpio_regmap_get_drvdata()
>> is used. At least that was its intention.
> 
> I would help the IC driver here too and just directly provide the
> drvdata pointer as argument. I don't see much value in providing the
> regmap_gpio pointer as IC driver can not dereference it.

What is it with the "it's useless if one cannot dereference it"? You're
also passing "struct regmap *" which you cannot dereference. It's an
opaque pointer you need to pass to gpio_regmap to call a function there.

What is the problem with letting gpio_regmap derefence its internal data
structure and return the value for you?

Adding the drvdata to reg_mask_xlate() highlights my former concern; you
need to keep chaning the users to add another parameter. What if xlate()
needs the regmap, too? Then you need to change it again. Granted this is
a silly example, but you should get my point. It is by far more easy to
just add another new gpio_regmap_*(struct gpio_regmap *) function and
you don't have to change existing users.

Also what if gpio_regmap provides some useful helper function in the
future, it will likely need its internal data struct.

-michael