linux-kernel - Re: [PATCH v9 2/2] input: joystick: Add ADC attached joystick driver.

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Date:   Sun, 6 Sep 2020 12:22:09 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Artur Rojek <contact@...ur-rojek.eu>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Cameron <jic23@...nel.org>,
        Paul Cercueil <paul@...pouillou.net>,
        Heiko Stuebner <heiko@...ech.de>,
        Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
        linux-input <linux-input@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 2/2] input: joystick: Add ADC attached joystick driver.

On Sat, Sep 5, 2020 at 7:34 PM Artur Rojek <contact@...ur-rojek.eu> wrote:
>
> Add a driver for joystick devices connected to ADC controllers
> supporting the Industrial I/O subsystem.

...

> +static int adc_joystick_handle(const void *data, void *private)
> +{
> +       struct adc_joystick *joy = private;
> +       enum iio_endian endianness;
> +       int bytes, msb, val, idx, i;
> +       bool sign;
> +
> +       bytes = joy->chans[0].channel->scan_type.storagebits >> 3;
> +
> +       for (i = 0; i < joy->num_chans; ++i) {
> +               idx = joy->chans[i].channel->scan_index;
> +               endianness = joy->chans[i].channel->scan_type.endianness;
> +               msb = joy->chans[i].channel->scan_type.realbits - 1;

> +               sign = (tolower(joy->chans[i].channel->scan_type.sign) == 's');

Redundant parentheses.

> +               switch (bytes) {
> +               case 1:
> +                       val = ((const u8 *)data)[idx];
> +                       break;
> +               case 2:

> +                       if (endianness == IIO_BE)
> +                               val = be16_to_cpu(((const __be16 *)data)[idx]);
> +                       else if (endianness == IIO_LE)
> +                               val = le16_to_cpu(((const __le16 *)data)[idx]);
> +                       else /* IIO_CPU */
> +                               val = ((const u16 *)data)[idx];
> +                       break;

Hmm... I don't like explicit castings to restricted types. On top of
that is it guaranteed that pointer to data will be aligned?
As a solution for the first two I would recommend to use
get_unaligned_be16() / get_unaligned_le16().
The last one is an interesting case and if data can be unaligned needs
to be fixed.

> +               default:
> +                       return -EINVAL;
> +               }
> +
> +               val >>= joy->chans[i].channel->scan_type.shift;
> +               if (sign)
> +                       val = sign_extend32(val, msb);
> +               else

> +                       val &= GENMASK(msb, 0);

It includes msb. Is it expected?

> +               input_report_abs(joy->input, joy->axes[i].code, val);
> +       }
> +
> +       input_sync(joy->input);
> +
> +       return 0;
> +}

...

> +static int adc_joystick_open(struct input_dev *dev)

> +static void adc_joystick_close(struct input_dev *dev)

Just wondering if this is protected against object lifetime cases.

...

> +err:

err_fwnode_put: ?

> +       fwnode_handle_put(child);
> +       return ret;

...

> +       /* Count how many channels we got. NULL terminated. */
> +       for (i = 0; joy->chans[i].indio_dev; ++i) {
> +               bits = joy->chans[i].channel->scan_type.storagebits;
> +               if (!bits || (bits > 16)) {
> +                       dev_err(dev, "Unsupported channel storage size\n");

> +                       return -EINVAL;

-ERANGE?

> +               }
> +               if (bits != joy->chans[0].channel->scan_type.storagebits) {
> +                       dev_err(dev, "Channels must have equal storage size\n");
> +                       return -EINVAL;
> +               }
> +       }

-- 
With Best Regards,
Andy Shevchenko