linux-kernel - Re: [PATCH] HID: cp2112: fix gpio value in gpio_direction

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Date:	Mon, 7 Jul 2014 10:03:29 -0400
From:	Benjamin Tissoires <benjamin.tissoires@...il.com>
To:	Antonio Borneo <borneo.antonio@...il.com>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	linux-input <linux-input@...r.kernel.org>,
	David Barksdale <dbarksdale@...ogix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] HID: cp2112: fix gpio value in gpio_direction_output

On Sun, Jun 29, 2014 at 2:13 AM, Antonio Borneo
<borneo.antonio@...il.com> wrote:
> CP2112 does not offer an atomic method to set both gpio
> direction and value.
> Also it does not permit to set gpio value before putting
> gpio in output. In fact, accordingly to Silicon Labs
> AN495, Rev. 0.2, cpt. 4.4, the HID report to set gpio
> values "does not affect any pins that are not configured
> as outputs".
>
> This is confirmed on evaluation board CP2112-EK.
> With current driver, after execute:
>         echo in > /sys/class/gpio/gpio248/direction
>         echo low > /sys/class/gpio/gpio248/direction
> gpio output is still high. Only after a following
>         echo low > /sys/class/gpio/gpio248/direction
> gpio output gets low.
>
> Fix driver by changing order of operations; first set
> direction then set value.
>
> The drawback of this new sequence is that we can have
> a pulse on gpio pin when direction is changed from
> input to output-low, but this cannot be avoided on
> current CP2112.

In this case, does keeping the first cp2112_gpio_set() before setting
the output direction prevents the pulse?
If so, then you can just keep the current code, and simply add the
cp2112_gpio_set() at the end of cp2112_gpio_direction_output().

In both case, this is:
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>

Cheers,
Benjamin

>
> Signed-off-by: Antonio Borneo <borneo.antonio@...il.com>
> ---
>  drivers/hid/hid-cp2112.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hid/hid-cp2112.c b/drivers/hid/hid-cp2112.c
> index 56be85a..3952d90 100644
> --- a/drivers/hid/hid-cp2112.c
> +++ b/drivers/hid/hid-cp2112.c
> @@ -240,8 +240,6 @@ static int cp2112_gpio_direction_output(struct gpio_chip *chip,
>         u8 buf[5];
>         int ret;
>
> -       cp2112_gpio_set(chip, offset, value);
> -
>         ret = hid_hw_raw_request(hdev, CP2112_GPIO_CONFIG, buf,
>                                        sizeof(buf), HID_FEATURE_REPORT,
>                                        HID_REQ_GET_REPORT);
> @@ -260,6 +258,12 @@ static int cp2112_gpio_direction_output(struct gpio_chip *chip,
>                 return ret;
>         }
>
> +       /*
> +        * Set gpio value when output direction is already set,
> +        * as specified in AN495, Rev. 0.2, cpt. 4.4
> +        */
> +       cp2112_gpio_set(chip, offset, value);
> +
>         return 0;
>  }
>
> --
> 2.0.1
>
> --
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