Re: [PATCH] ads7846: enable usage of internal vref for AD7873

[Michael Hennerich <michael.hennerich@analog.com>]

On 05/29/2012 05:22 PM, Markus Niebel wrote:
> Touchscreen samples are taken in differential mode.
> Therefore an external reference is not needed.
> When working with internal vref disabling vref after
> every touchscreen sample leads to settling effects in sampling
> and errors in position data.
>
> This patch disables the internal vref only if keep_vref_on us
> is not set in platform_data.
>
> Tested on i.MX35 with costum board
>
>
> Signed-off-by: Markus Niebel<Markus.Niebel@tqs.de>
> ---
>   drivers/input/touchscreen/ads7846.c |    9 ++++-----
>   1 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
> index f02028e..b271633 100644
> --- a/drivers/input/touchscreen/ads7846.c
> +++ b/drivers/input/touchscreen/ads7846.c
> @@ -1001,15 +1001,14 @@ static void __devinit ads7846_setup_spi_msg(struct ads7846 *ts,
>          struct ads7846_packet *packet = ts->packet;
>          int vref = pdata->keep_vref_on;
>
> -       if (ts->model == 7873) {
> +       if (ts->model == 7873)
>                  /*
>                   * The AD7873 is almost identical to the ADS7846
> -                * keep VREF off during differential/ratiometric
> -                * conversion modes.
> +                * set VREF off during differential/ratiometric
> +                * conversion modes if keep_vref_on is not set.
> +                * TODO: does keep_vref_on collide with usage of external vref?
>                   */
>                  ts->model = 7846;
> -               vref = 0;
> -       }

I would scrap this section from ads7846_setup_spi_msg() completely
and force ts->model to 7846 in ads7846_probe() when 7873 is specified.

>
>          ts->msg_count = 1;
>          spi_message_init(m);
> --
> 1.7.0.4
>


-- 
Greetings,
Michael

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