linux-kernel - Re: [PATCH] staging: wfx: fix reset GPIO polarity

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Message-ID: <20191206175728.GA20259@qmqm.qmqm.pl>
Date:   Fri, 6 Dec 2019 18:57:28 +0100
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Jérôme Pouiller <Jerome.Pouiller@...abs.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: wfx: fix reset GPIO polarity

On Thu, Dec 05, 2019 at 03:43:49PM +0000, Jérôme Pouiller wrote:
> On Thursday 5 December 2019 15:49:55 CET Michał Mirosław wrote:
> > On Thu, Dec 05, 2019 at 02:08:23PM +0000, Jérôme Pouiller wrote:
> > > On Wednesday 4 December 2019 17:59:46 CET Michał Mirosław wrote:
> > > > Driver inverts meaning of GPIO_ACTIVE_LOW/HIGH. Fix it to prevent
> > > > confusion.
> > > >
> > > > Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> > > > ---
> > > >  drivers/staging/wfx/bus_spi.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/staging/wfx/bus_spi.c b/drivers/staging/wfx/bus_spi.c
> > > > index ab0cda1e124f..73d0157a86ba 100644
> > > > --- a/drivers/staging/wfx/bus_spi.c
> > > > +++ b/drivers/staging/wfx/bus_spi.c
> > > > @@ -199,9 +199,9 @@ static int wfx_spi_probe(struct spi_device *func)
> > > >         if (!bus->gpio_reset) {
> > > >                 dev_warn(&func->dev, "try to load firmware anyway\n");
> > > >         } else {
> > > > -               gpiod_set_value(bus->gpio_reset, 0);
> > > > -               udelay(100);
> > > >                 gpiod_set_value(bus->gpio_reset, 1);
> > > > +               udelay(100);
> > > > +               gpiod_set_value(bus->gpio_reset, 0);
> > > >                 udelay(2000);
> > > >         }
> > > Hello Michał,
> > >
> > > I did not find real consensus in kernel code. My personal taste would
> > > be to keep this gpio "ACTIVE_HIGH" and rename it gpio_nreset. What do
> > > you think about it?
> > >
> > > (in add, this solution would explicitly change the name of the DT
> > > attribute instead of changing the semantic of the existing attribute)
> > 
> > As a user (board developer) I would expect that DT describes the
> > GPIO meaning directly: so when I specify GPIO_ACTIVE_HIGH flag I also
> > wire up the board so that outputing 1 would match the active state of
> > the chip's signal (that might be inverted for some reason). I think we
> > should stick to what is said in Documentation/devicetree/bindings/gpio.txt
> > (section 1.1).
> > 
> > Since this is a new driver in kernel I would prefer to fix it at the start.
> > Changing the name of the GPIO would also be ok, but since there is no DT
> > binding yet, I guess there will come up an issue of 'compatible' string
> > format that does not match 'vendor,chip' now, so we can use the difference
> > for backwards compatibility with out-of-tree driver if needed.
> 
> Current 'compatible' string is "silabs,wfx-spi" (for now, it is the
> same for out-of-tree and in-tree driver). And indeed, "wfx" does not
> names a chip.
> 
> The three chips currently supported are wf200, wf200s and wfm200. Since
> the driver provides DT bindings for SPI and SDIO buses, I think we
> have to keep the "-spi" suffix. So compatible strings should be
> "silabs,wf200-spi", "silabs,wf200s-spi" and "silabs,wfm200-spi", right?
[...]

I wonder if the '-spi' part is necessary? The interface is determined by
putting device node as a child of an SPI or MMC controller node. Kernel
won't probe SPI driver for MMC device anyway (nor the other way around).

Best Regards
Michał Mirosław