linux-kernel - Re: [PATCH v3 4/6] bus: add driver for the Technologic Systems NBUS

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Date:   Thu, 11 May 2017 15:56:00 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Sebastien Bourdelin <sebastien.bourdelin@...oirfairelinux.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-watchdog@...r.kernel.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        kernel <kernel@...oirfairelinux.com>,
        Rob Herring <robh@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Shawn Guo <shawnguo@...nel.org>,
        Fabio Estevam <fabio.estevam@....com>,
        Mark Featherston <mark@...eddedarm.com>, kris@...eddedarm.com
Subject: Re: [PATCH v3 4/6] bus: add driver for the Technologic Systems NBUS

On Fri, May 5, 2017 at 9:32 PM, Sebastien Bourdelin
<sebastien.bourdelin@...oirfairelinux.com> wrote:

> This driver implements a GPIOs bit-banged bus, called the NBUS by
> Technologic Systems. It is used to communicate with the peripherals in
> the FPGA on the TS-4600 SoM.
>
> Signed-off-by: Sebastien Bourdelin <sebastien.bourdelin@...oirfairelinux.com>
> ---
> Changes v2 -> v3:

This driver is pretty.
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

For future development (that is not about this patch, please
merge this):

> +static int ts_nbus_read_byte(struct ts_nbus *ts_nbus, u8 *val)
> +{
> +       struct gpio_descs *gpios = ts_nbus->data;
> +       int ret, i;
> +
> +       *val = 0;
> +       for (i = 0; i < 8; i++) {
> +               ret = gpiod_get_value_cansleep(gpios->desc[i]);
> +               if (ret < 0)
> +                       return ret;
> +               if (ret)
> +                       *val |= BIT(i);
> +       }
> +
> +       return 0;
> +}

That makes it pretty obvious that we really need gpiod_get_array_cansleep()
does it not. That would just become some single register read in
this case.

If you get some time one of these days and wand to have a go at adding
it to gpiolib using this driver as a testbed, do not hesitate.

Yours,
Linus Walleij