linux-kernel - Re: [PATCH v2 2/2] gpio: Add Cadence GPIO driver

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Date:   Tue, 18 Dec 2018 13:54:25 +0000
From:   Janek Kotas <jank@...ence.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
CC:     Linus Walleij <linus.walleij@...aro.org>,
        Janek Kotas <jank@...ence.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        linux-devicetree <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] gpio: Add Cadence GPIO driver


> On 18 Dec 2018, at 13:50, Bartosz Golaszewski <bgolaszewski@...libre.com> wrote:
> 
> 
> pon., 17 gru 2018 o 23:22 Linus Walleij <linus.walleij@...aro.org> napisał(a):
>> 
>> On Mon, Dec 17, 2018 at 4:51 PM Bartosz Golaszewski
>> <bgolaszewski@...libre.com> wrote:
>> 
>>> The driver looks good but is there any particular reason not to use
>>> regmap for register IO?
>> 
>> I thought we only use regmap for MMIO when the register range is
>> shared (as in a system controller) so that some registers are for this,
>> some register or even bits in a register for some other driver, so they
>> need the spinlock in the regmap to protect the register range.
>> 
> 
> This is what syscon is for. Regmap simply abstracts any register IO.
> For instance: there's no locking in this driver. Are we sure it's not
> needed? Regmap provides internal locking for you in the form of a
> mutex or spinlock.
> 
> Also: it looks like the interrupts here are quite simple with a single
> bit per interrupt in the status register and the same layout in the
> mask register - it could probably profit from using the
> regmap_irq_chip and not bother with reimplementing irq_chip callbacks.
> 
>> It is also nice for shadowing/caching of register contents I guess,
>> wat does this driver get from regmap MMIO?
>> 
> 
> Code shrinkage IMO.
> 
> Note that I'm not blocking this from being merged - I just think that
> using modern frameworks is always a good idea.

I can reimplement the driver using regmap, but It seems in such case
I won’t be able to use the Generic GPIO Infrastructure, would I?
So I would need to provide functions for setting direction, etc.
I think it would make the driver code bigger.

Regards,
Jan

> Best regards,
> Bartosz Golaszewski
> 
>> Yours,
>> Linus Walleij