linux-kernel - Re: [PATCH] staging: fbtft: Changed calls to udelays() functions for usleep

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Message-ID: <20240922215914.uK2pDGCw@linutronix.de>
Date: Sun, 22 Sep 2024 23:59:14 +0200
From: Nam Cao <namcao@...utronix.de>
To: Fabio <joakobar2000@...il.com>
Cc: dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
	linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org
Subject: Re: [PATCH] staging: fbtft: Changed calls to udelays() functions for
 usleep_range()

On Sun, Sep 22, 2024 at 09:12:13AM -0300, Fabio wrote:
> Replaced two lines of calling  udelays by usleep_range() functions, adding
> more efficiency due to the need of long-lasting delays of more than 10us.
> 
> Signed-off-by: Fabio Bareiro <joakobar2000@...il.com>
> ---
>  drivers/staging/fbtft/fb_ra8875.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/fbtft/fb_ra8875.c b/drivers/staging/fbtft/fb_ra8875.c
> index 0ab1de6647d0..edd467c6bf1a 100644
> --- a/drivers/staging/fbtft/fb_ra8875.c
> +++ b/drivers/staging/fbtft/fb_ra8875.c
> @@ -210,7 +210,7 @@ static void write_reg8_bus8(struct fbtft_par *par, int len, ...)
>  	}
>  	len--;
>  
> -	udelay(100);
> +	usleep_range(100, 150);
>  
>  	if (len) {
>  		buf = (u8 *)par->buf;
> @@ -231,7 +231,7 @@ static void write_reg8_bus8(struct fbtft_par *par, int len, ...)
>  
>  	/* restore user spi-speed */
>  	par->fbtftops.write = fbtft_write_spi;
> -	udelay(100);
> +	usleep_range(100, 150);
>  }

Are you sure that these changes are safe to make? If this write_reg8_bus8()
function is ever called in atomic context, this patch would break the
driver.

Unless it can be verified with hardware, I wouldn't make this kind of
changes.

Best regards,
Nam