linux-kernel - Re: [PATCH v2 3/4] gpio: Add RDA Micro GPIO controller support

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Date:   Mon, 21 Oct 2019 11:49:26 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-unisoc@...ts.infradead.org,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Orson Zhai <orsonzhai@...il.com>
Subject: Re: [PATCH v2 3/4] gpio: Add RDA Micro GPIO controller support

Hi Linus,

On Mon, Oct 21, 2019 at 02:57:31AM +0200, Linus Walleij wrote:
> On Sat, Oct 19, 2019 at 6:05 PM Manivannan Sadhasivam
> <manivannan.sadhasivam@...aro.org> wrote:
> > On Wed, Oct 16, 2019 at 02:41:32PM +0200, Linus Walleij wrote:
> 
> > > select GPIO_GENERIC
> >
> > hmm.. I don't think this driver can use it. Please see the justification
> > below.
> (...)
> > As you can see in this driver, there are 2 separate registers needs to be
> > read in order to get the value. RDA_GPIO_VAL needs to be read when the pin
> > is in input state and RDA_GPIO_SET needs to be read when the pin is in output
> > state.
> >
> > The MMIO driver relies on a single `dat` register to read the GPIO state and
> > this won't fit for this driver and hence my justification for not using it.
> 
> Use RDA_GPIO_VAL for dat, then set BGPIOF_READ_OUTPUT_REG_SET
> and the mmio core will do what you want I think? That's what the flag is
> for IIUC.
> 

Ah, this should work. Sorry for missing this earlier.

> Maybe we should document it better :/
> 

That's how everything is in kernel for me... If you don't look closer, you'll
not get it.

Thanks,
Mani

> Yours,
> Linus Walleij