[PATCH] staging: fbtft: fb_ra8875: replace udelays with usleep_range

[PATCH] staging: fbtft: fb_ra8875: replace udelays with usleep_range

[Jose A. Perez de Azpillaga]

The write_reg8_bus8 function uses udelay(100) twice to wait for the
display controller. For delays of this duration in non-atomic context,
usleep_range() is preferred as it avoids busy-waiting.

Update both instances to use usleep_range(100, 120), allowing the
scheduler to utilize the CPU during these wait periods.

Signed-off-by: Jose A. Perez de Azpillaga <azpijr@gmail.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..6058934e2ca2 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, 120);
 
 	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, 120);
 }
 
 static int write_vmem16_bus8(struct fbtft_par *par, size_t offset, size_t len)
-- 
2.53.0

Re: [PATCH] staging: fbtft: fb_ra8875: replace udelays with usleep_range

[Greg KH]

On Wed, Feb 25, 2026 at 09:45:59PM +0100, Jose A. Perez de Azpillaga wrote:
> The write_reg8_bus8 function uses udelay(100) twice to wait for the
> display controller. For delays of this duration in non-atomic context,
> usleep_range() is preferred as it avoids busy-waiting.
> 
> Update both instances to use usleep_range(100, 120), allowing the
> scheduler to utilize the CPU during these wait periods.
> 
> Signed-off-by: Jose A. Perez de Azpillaga <azpijr@gmail.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..6058934e2ca2 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, 120);
>  
>  	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, 120);
>  }
>  
>  static int write_vmem16_bus8(struct fbtft_par *par, size_t offset, size_t len)
> -- 
> 2.53.0
> 
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- You sent a patch that has been sent multiple times in the past few
  days, and is identical to ones that has been recently rejected.
  Please always look at the mailing list traffic to determine if you are
  duplicating other people's work.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.

thanks,

greg k-h's patch email bot

[PATCH v2] staging: fbtft: fb_ra8875: replace udelays with fsleep

[Jose A. Perez de Azpillaga]

The write_reg8_bus8 function uses udelay(100) twice to wait for the
display controller. In non-atomic contexts, fsleep() is the preferred
API as it automatically selects the most efficient sleeping mechanism
and avoids busy-waiting.

Update both instances to use fsleep(100).

Signed-off-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
---
v2: Switch from usleep_range() to fsleep() for modernizing delay calls.
---
 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..fe95ec6da064 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);
+	fsleep(100);

 	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);
+	fsleep(100);
 }

 static int write_vmem16_bus8(struct fbtft_par *par, size_t offset, size_t len)
--
2.53.0

Re: [PATCH v2] staging: fbtft: fb_ra8875: replace udelays with fsleep

[Andy Shevchenko]

On Thu, Feb 26, 2026 at 12:40:36AM +0100, Jose A. Perez de Azpillaga wrote:
> The write_reg8_bus8 function uses udelay(100) twice to wait for the

write_reg8_bus8()

> display controller. In non-atomic contexts, fsleep() is the preferred
> API as it automatically selects the most efficient sleeping mechanism
> and avoids busy-waiting.

But how do you know this is the non-atomic context?

> Update both instances to use fsleep(100).

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2] staging: fbtft: fb_ra8875: replace udelays with fsleep

[Jose A. Perez de Azpillaga]

Hi Andy,

write_reg8_bus8() calls par->fbtftops.write(), which in this driver
resolves to write_spi(), which calls spi_sync(). Since spi_sync()
requires sleepable context, write_reg8_bus8() is transitively guaranteed
to run in non-atomic context, making fsleep() safe to use.

Best regards, Jose