linux-kernel - Re: [PATCH 1/3] powerpc: Add mmc-spi-slot bindings

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Message-ID: <fa686aa40810301337p21ac8785gb74b12904bbd08e7@mail.gmail.com>
Date:	Thu, 30 Oct 2008 14:37:31 -0600
From:	"Grant Likely" <grant.likely@...retlab.ca>
To:	"Anton Vorontsov" <avorontsov@...mvista.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	"David Brownell" <dbrownell@...rs.sourceforge.net>,
	"Pierre Ossman" <drzeus-mmc@...eus.cx>
Subject: Re: [PATCH 1/3] powerpc: Add mmc-spi-slot bindings

On Thu, Oct 30, 2008 at 1:56 PM, Anton Vorontsov
<avorontsov@...mvista.com> wrote:
> The bindings describes a case where MMC/SD/SDIO slot directly connected
> to a SPI bus. Such setups are widely used on embedded PowerPC boards.
>
> The patch also adds the mmc-spi-slot entry to the OpenFirmware modalias
> table.
>
> Signed-off-by: Anton Vorontsov <avorontsov@...mvista.com>

Mostly looks good to me.  A few comments below.

> ---
>  .../powerpc/dts-bindings/mmc-spi-slot.txt          |   23 ++++++++++++++++++++
>  drivers/of/base.c                                  |    1 +
>  2 files changed, 24 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/powerpc/dts-bindings/mmc-spi-slot.txt
>
> diff --git a/Documentation/powerpc/dts-bindings/mmc-spi-slot.txt b/Documentation/powerpc/dts-bindings/mmc-spi-slot.txt
> new file mode 100644
> index 0000000..c39ac28
> --- /dev/null
> +++ b/Documentation/powerpc/dts-bindings/mmc-spi-slot.txt
> @@ -0,0 +1,23 @@
> +MMC/SD/SDIO slot directly connected to a SPI bus
> +
> +Required properties:
> +- compatible : should be "mmc-spi-slot".
> +- reg : should specify SPI address (chip-select number).
> +- spi-max-frequency : maximum frequency for this device (Hz).
> +- voltage-ranges : two cells are required, first cell specifies minimum
> +  slot voltage (mV), second cell specifies maximum slot voltage (mV).
> +  Several ranges could be specified.
> +- gpios : (optional) may specify GPIOs in this order: Card-Detect GPIO,
> +  Write-Protect GPIO.

I wonder if we're following the example of irq mappings too closely
for the gpios property.  I like the layout of the property
(<controller> <specifier>), but I think the 'gpios' name is getting
too overloaded.  In this case a single property 'gpios' is being used
to encode 2 unrelated bits of information; the write protect pin and
the card detect pins.

In this particular case I think it is better to use 2 properties in
this case; something like 'spi-writeprotect-gpio' and
'spi-carddetect-gpio' using the same specifier format.  Doing so adds
a bit more clarity to the purpose of the properties.

I my mind I differentiate this from other examples (for instance a
series of CS pins) based on how closely related the pin functions are.
 So I would say for the following examples...
1) GPIO data bus (SPI, MDIO and I2C are great examples); all pins must
be present - single gpio property
2) This MMC case (pins are optional and unrelated); separate gpio properties
3) LCD with backlight and contrast control pins; one gpio property for
backlight pins, one for constrast pins.

Thoughts?

> +
> +Example:
> +
> +       mmc-slot@0 {
> +               compatible = "fsl,mpc8323rdb-mmc-slot",
> +                            "mmc-spi-slot";
> +               reg = <0>;
> +               gpios = <&qe_pio_d 14 1
> +                        &qe_pio_d 15 0>;
> +               voltage-ranges = <3300 3300>;
> +               spi-max-frequency = <50000000>;
> +       };
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 7c79e94..c6797ca 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -411,6 +411,7 @@ struct of_modalias_table {
>  };
>  static struct of_modalias_table of_modalias_table[] = {
>        { "fsl,mcu-mpc8349emitx", "mcu-mpc8349emitx" },
> +       { "mmc-spi-slot", "mmc_spi" },
>  };
>
>  /**
> --
> 1.5.6.3
>
>



-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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