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From: Brad Larson <brad@pensando.io>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Serge Semin <fancer.lancer@gmail.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Mark Brown <broonie@kernel.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Olof Johansson <olof@lixom.net>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	linux-spi <linux-spi@vger.kernel.org>,
	linux-mmc <linux-mmc@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/8] gpio: Add Elba SoC gpio driver for spi cs control
Date: Sun, 22 Aug 2021 18:05:52 -0700	[thread overview]
Message-ID: <CAK9rFnzDZ4MNm68AJ75g7zegLD-7UMHyoVR-4ssitYTTEeQm5g@mail.gmail.com> (raw)
In-Reply-To: <CACRpkdZroi+_oHqipS71MAGif190y7jWU5Myf55vz=_um4w5cQ@mail.gmail.com>

Hi Linus,

On Thu, Mar 4, 2021 at 5:38 AM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Thu, Mar 4, 2021 at 10:10 AM Serge Semin <fancer.lancer@gmail.com> wrote:
> > On Thu, Mar 04, 2021 at 09:29:33AM +0100, Linus Walleij wrote:
>
> > > > + * pin:             3            2        |       1            0
> > > > + * bit:         7------6------5------4----|---3------2------1------0
> > > > + *             cs1  cs1_ovr  cs0  cs0_ovr |  cs1  cs1_ovr  cs0  cs0_ovr
> > > > + *                        ssi1            |             ssi0
> > > > + */
> > > > +#define SPICS_PIN_SHIFT(pin)   (2 * (pin))
> > > > +#define SPICS_MASK(pin)                (0x3 << SPICS_PIN_SHIFT(pin))
> > > > +#define SPICS_SET(pin, val)    ((((val) << 1) | 0x1) << SPICS_PIN_SHIFT(pin))
> > >
> >
> > > So 2 bits per GPIO line in one register? (Nice doc!)
> >
> > I suppose the first bit is the CS-pin-override flag. So when it's set
> > the output is directly driven by the second bit, otherwise the
> > corresponding DW APB SPI controller drives it. That's how the
> > multiplexing is implemented here.
>
> If these output lines are so tightly coupled to the SPI block
> and will not be used for any other GPO (general purpose output)
> I think it makes more sense to bundle the handling into the
> DW SPI driver, and activate it based on the Elba compatible
> string (if of_is_compatible(...)).
>
> I am a bit cautious because it has happened in the past that
> people repurpose CS lines who were originally for SPI CS
> to all kind of other purposes, such as a power-on LED and
> in that case it needs to be a separate GPIO driver. So the
> author needs to have a good idea about what is a realistic
> use case here.

The gpio pins being used for the Elba SoC SPI CS are dedicated to this
function.  Are you recommending that the code in
drivers/gpio/gpio-elba-spics.c be integrated into
drivers/spi/spi-dw-mmio.c?

Regards,
Brad

  reply	other threads:[~2021-08-23  1:06 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-04  3:41 [PATCH 0/8] Support Pensando Elba SoC Brad Larson
2021-03-04  3:41 ` [PATCH 1/8] gpio: Add Elba SoC gpio driver for spi cs control Brad Larson
2021-03-04  8:29   ` Linus Walleij
2021-03-04  9:10     ` Serge Semin
2021-03-04 13:38       ` Linus Walleij
2021-08-23  1:05         ` Brad Larson [this message]
2021-08-29 21:09           ` Linus Walleij
2021-10-04 16:46             ` Brad Larson
2021-10-12 23:51               ` Linus Walleij
2021-10-14 20:06                 ` Brad Larson
2021-03-30  2:44     ` Brad Larson
2021-08-23  1:05     ` Brad Larson
2021-03-04 20:43   ` Elliott, Robert (Servers)
2021-08-23  1:06     ` Brad Larson
2021-03-05 11:25   ` Krzysztof Kozlowski
2021-08-23  1:07     ` Brad Larson
2021-03-05 13:57   ` Geert Uytterhoeven
2021-08-23  1:08     ` Brad Larson
2021-03-07 19:21   ` Andy Shevchenko
2021-03-29  1:19     ` Brad Larson
2021-03-29 10:39       ` Andy Shevchenko
2021-08-23  1:13         ` Brad Larson
2021-08-23  7:50           ` Geert Uytterhoeven
2021-08-23 16:30             ` Brad Larson
2021-08-23 20:11               ` Geert Uytterhoeven
2021-10-04 17:14                 ` Brad Larson
2021-10-04 17:16                   ` Geert Uytterhoeven
2021-08-23  1:10     ` Brad Larson
2021-03-04  3:41 ` [PATCH 2/8] spi: cadence-quadspi: Add QSPI support for Pensando Elba SoC Brad Larson
2021-03-04  9:29   ` Arnd Bergmann
2021-03-04  3:41 ` [PATCH 3/8] spi: dw: Add support for Pensando Elba SoC SPI Brad Larson
2021-03-04  6:44   ` Serge Semin
2021-08-23  1:17     ` Brad Larson
2021-03-04  8:48   ` Linus Walleij
2021-03-10  3:52     ` Brad Larson
2021-03-04  3:41 ` [PATCH 4/8] spidev: Add Pensando CPLD compatible Brad Larson
2021-03-04  9:33   ` Arnd Bergmann
2021-03-04  3:41 ` [PATCH 5/8] mmc: sdhci-cadence: Add Pensando Elba SoC support Brad Larson
2021-03-04  9:41   ` Arnd Bergmann
2021-03-04  3:41 ` [PATCH 6/8] arm64: Add config for Pensando SoC platforms Brad Larson
2021-03-04  9:42   ` Arnd Bergmann
2021-03-04  3:41 ` [PATCH 7/8] arm64: dts: Add Pensando Elba SoC support Brad Larson
2021-03-04  8:03   ` Serge Semin
2021-03-29  1:07     ` Brad Larson
2021-08-23  0:54     ` Brad Larson
2021-03-04  8:51   ` Linus Walleij
2021-03-29  0:54     ` Brad Larson
2021-03-04  9:06   ` Arnd Bergmann
2021-03-04 20:47   ` Rob Herring
2021-03-05 11:22   ` Krzysztof Kozlowski
2021-03-04  3:41 ` [PATCH 8/8] MAINTAINERS: Add entry for PENSANDO Brad Larson

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