linux-kernel - Re: [PATCH v2 1/6] staging: fbtft: convert fbtft

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Date:   Tue, 3 Jan 2017 18:22:09 +0100
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/6] staging: fbtft: convert fbtft_reset() to be
 non-atomic


Den 02.01.2017 12:35, skrev Andy Shevchenko:
> First of all, fbtft in current state doesn't allow to override GPIOs to be
> optional, like "reset" one. It might be a bug somewhere, but rather out of
> scope of this fix.
>
> Second, not all GPIOs available on the board would be SoC based, some of them
> might sit on I2C GPIO expanders, for example, on Intel Edison/Arduino, and thus
> any communication with them might sleep.
>
> Besides that using udelay() and mdelay() is kinda resource wasteful.
>
> Summarize all of the above, convert fbtft_reset() function to non-atomic
> variant by using gpio_set_value_cansleep(), usleep_range(), and msleep().
>
> To avoid potential use in atomic context annotate it via might_sleep() macro.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>   drivers/staging/fbtft/fbtft-core.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
> index bbe89c9c4fb9..e8bf0d1ec11f 100644
> --- a/drivers/staging/fbtft/fbtft-core.c
> +++ b/drivers/staging/fbtft/fbtft-core.c
> @@ -336,11 +336,14 @@ static void fbtft_reset(struct fbtft_par *par)
>   {
>   	if (par->gpio.reset == -1)
>   		return;
> +
> +	might_sleep();

gpio_set_value_cansleep() already does might_sleep().
So with that removed:
Reviewed-by: Noralf Trønnes <noralf@...nnes.org>

> +
>   	fbtft_par_dbg(DEBUG_RESET, par, "%s()\n", __func__);
> -	gpio_set_value(par->gpio.reset, 0);
> -	udelay(20);
> -	gpio_set_value(par->gpio.reset, 1);
> -	mdelay(120);
> +	gpio_set_value_cansleep(par->gpio.reset, 0);
> +	usleep_range(20, 40);
> +	gpio_set_value_cansleep(par->gpio.reset, 1);
> +	msleep(120);
>   }
>   
>   static void fbtft_update_display(struct fbtft_par *par, unsigned int start_line,