[PATCH] fbtft: Improve damage_range to mark only changed rows

[PATCH] fbtft: Improve damage_range to mark only changed rows

[Waffle0823]

Instead of marking the entire display as dirty, calculate
start_row and end_row based on off/len and mark only those rows.
This improves performance for partial framebuffer updates.

Signed-off-by: Waffle0283 csshin9928@gmail.com
---
 drivers/staging/fbtft/fbtft-core.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
index 8a5ccc8ae0a1..0fbdfdaaa94d 100644
--- a/drivers/staging/fbtft/fbtft-core.c
+++ b/drivers/staging/fbtft/fbtft-core.c
@@ -415,8 +415,11 @@ static void fbtft_ops_damage_range(struct fb_info *info, off_t off, size_t len)
 {
 	struct fbtft_par *par = info->par;
 
-	/* TODO: only mark changed area update all for now */
-	par->fbtftops.mkdirty(info, -1, 0);
+	__u32 width = info->var.xres;
+	__u32 start_row = off / width;
+	__u32 end_row = (off + len - 1) / width;
+
+	par->fbtftops.mkdirty(info, start_row, end_row);
 }
 
 static void fbtft_ops_damage_area(struct fb_info *info, u32 x, u32 y, u32 width, u32 height)
-- 
2.52.0

Re: [PATCH] fbtft: Improve damage_range to mark only changed rows

[Greg KH]

On Wed, Jan 28, 2026 at 05:57:20PM +0900, Waffle0823 wrote:
> Instead of marking the entire display as dirty, calculate
> start_row and end_row based on off/len and mark only those rows.
> This improves performance for partial framebuffer updates.
> 
> Signed-off-by: Waffle0283 csshin9928@gmail.com
> ---
>  drivers/staging/fbtft/fbtft-core.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
> index 8a5ccc8ae0a1..0fbdfdaaa94d 100644
> --- a/drivers/staging/fbtft/fbtft-core.c
> +++ b/drivers/staging/fbtft/fbtft-core.c
> @@ -415,8 +415,11 @@ static void fbtft_ops_damage_range(struct fb_info *info, off_t off, size_t len)
>  {
>  	struct fbtft_par *par = info->par;
>  
> -	/* TODO: only mark changed area update all for now */
> -	par->fbtftops.mkdirty(info, -1, 0);
> +	__u32 width = info->var.xres;
> +	__u32 start_row = off / width;
> +	__u32 end_row = (off + len - 1) / width;
> +
> +	par->fbtftops.mkdirty(info, start_row, end_row);
>  }
>  
>  static void fbtft_ops_damage_area(struct fb_info *info, u32 x, u32 y, u32 width, u32 height)
> -- 
> 2.52.0
> 

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:

- It looks like you did not use your "real" name for the patch on either
  the Signed-off-by: line, or the From: line (both of which have to
  match).  Please read the kernel file,
  Documentation/process/submitting-patches.rst for how to do this
  correctly.

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] fbtft: Improve damage_range to mark only changed rows

[Waffle0823]

Instead of marking the entire display as dirty, calculate
start_row and end_row based on off/len and mark only those rows.
This improves performance for partial framebuffer updates.

Signed-off-by: Waffle0823 <csshin9928@gmail.com>
---
 drivers/staging/fbtft/fbtft-core.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
index 8a5ccc8ae0a1..0fbdfdaaa94d 100644
--- a/drivers/staging/fbtft/fbtft-core.c
+++ b/drivers/staging/fbtft/fbtft-core.c
@@ -415,8 +415,11 @@ static void fbtft_ops_damage_range(struct fb_info *info, off_t off, size_t len)
 {
 	struct fbtft_par *par = info->par;
 
-	/* TODO: only mark changed area update all for now */
-	par->fbtftops.mkdirty(info, -1, 0);
+	__u32 width = info->var.xres;
+	__u32 start_row = off / width;
+	__u32 end_row = (off + len - 1) / width;
+
+	par->fbtftops.mkdirty(info, start_row, end_row);
 }
 
 static void fbtft_ops_damage_area(struct fb_info *info, u32 x, u32 y, u32 width, u32 height)
-- 
2.52.0

Re: [PATCH] fbtft: Improve damage_range to mark only changed rows

[Greg KH]

On Wed, Jan 28, 2026 at 06:22:10PM +0900, Waffle0823 wrote:
> Instead of marking the entire display as dirty, calculate
> start_row and end_row based on off/len and mark only those rows.
> This improves performance for partial framebuffer updates.
> 
> Signed-off-by: Waffle0823 <csshin9928@gmail.com>
> ---
>  drivers/staging/fbtft/fbtft-core.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
> index 8a5ccc8ae0a1..0fbdfdaaa94d 100644
> --- a/drivers/staging/fbtft/fbtft-core.c
> +++ b/drivers/staging/fbtft/fbtft-core.c
> @@ -415,8 +415,11 @@ static void fbtft_ops_damage_range(struct fb_info *info, off_t off, size_t len)
>  {
>  	struct fbtft_par *par = info->par;
>  
> -	/* TODO: only mark changed area update all for now */
> -	par->fbtftops.mkdirty(info, -1, 0);
> +	__u32 width = info->var.xres;
> +	__u32 start_row = off / width;
> +	__u32 end_row = (off + len - 1) / width;
> +
> +	par->fbtftops.mkdirty(info, start_row, end_row);
>  }
>  
>  static void fbtft_ops_damage_area(struct fb_info *info, u32 x, u32 y, u32 width, u32 height)
> -- 
> 2.52.0
> 
> 

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:

- It looks like you did not use your "real" name for the patch on either
  the Signed-off-by: line, or the From: line (both of which have to
  match).  Please read the kernel file,
  Documentation/process/submitting-patches.rst for how to do this
  correctly.

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] fbtft: Improve damage_range to mark only changed rows

[ChanSoo Shin]

Instead of marking the entire display as dirty, calculate
start_row and end_row based on off/len and mark only those rows.
This improves performance for partial framebuffer updates.

Signed-off-by: ChanSoo Shin <csshin9928@gmail.com>
---
 drivers/staging/fbtft/fbtft-core.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
index 8a5ccc8ae0a1..0fbdfdaaa94d 100644
--- a/drivers/staging/fbtft/fbtft-core.c
+++ b/drivers/staging/fbtft/fbtft-core.c
@@ -415,8 +415,11 @@ static void fbtft_ops_damage_range(struct fb_info *info, off_t off, size_t len)
 {
 	struct fbtft_par *par = info->par;
 
-	/* TODO: only mark changed area update all for now */
-	par->fbtftops.mkdirty(info, -1, 0);
+	__u32 width = info->var.xres;
+	__u32 start_row = off / width;
+	__u32 end_row = (off + len - 1) / width;
+
+	par->fbtftops.mkdirty(info, start_row, end_row);
 }
 
 static void fbtft_ops_damage_area(struct fb_info *info, u32 x, u32 y, u32 width, u32 height)
-- 
2.52.0

Re: [PATCH] fbtft: Improve damage_range to mark only changed rows

[Dan Carpenter]

On Wed, Jan 28, 2026 at 05:57:20PM +0900, Waffle0823 wrote:
> Instead of marking the entire display as dirty, calculate
> start_row and end_row based on off/len and mark only those rows.
> This improves performance for partial framebuffer updates.
> 
> Signed-off-by: Waffle0283 csshin9928@gmail.com

Please use your real name that you use to sign legal documents.  The
email address is in the wrong format.

Have you tested this patch?  What was the speedup?

regards,
dan carpenter

Re: [PATCH] fbtft: Improve damage_range to mark only changed rows

[Dan Carpenter]

On Wed, Jan 28, 2026 at 10:05:03PM +0900, ChanSoo Shin wrote:
> Instead of marking the entire display as dirty, calculate
> start_row and end_row based on off/len and mark only those rows.
> This improves performance for partial framebuffer updates.
> 
> Signed-off-by: ChanSoo Shin <csshin9928@gmail.com>
> ---

This is v3 but it's not marked or described.

Have you tested this patch?  What was the speed up?

regards,
dan carpenter

Re: [PATCH] fbtft: Improve damage_range to mark only changed rows

[Nam Cao]

ChanSoo Shin <csshin9928@gmail.com> writes:
> Instead of marking the entire display as dirty, calculate
> start_row and end_row based on off/len and mark only those rows.
> This improves performance for partial framebuffer updates.
>
> Signed-off-by: ChanSoo Shin <csshin9928@gmail.com>
> ---
>  drivers/staging/fbtft/fbtft-core.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
> index 8a5ccc8ae0a1..0fbdfdaaa94d 100644
> --- a/drivers/staging/fbtft/fbtft-core.c
> +++ b/drivers/staging/fbtft/fbtft-core.c
> @@ -415,8 +415,11 @@ static void fbtft_ops_damage_range(struct fb_info *info, off_t off, size_t len)
>  {
>  	struct fbtft_par *par = info->par;
>  
> -	/* TODO: only mark changed area update all for now */
> -	par->fbtftops.mkdirty(info, -1, 0);
> +	__u32 width = info->var.xres;
> +	__u32 start_row = off / width;
> +	__u32 end_row = (off + len - 1) / width;
> +
> +	par->fbtftops.mkdirty(info, start_row, end_row);

This doesn't look right: mkdirty() takes start row and number of rows,
not start row and end row. Don't be fooled by how mkdirty() is declared,
look at how it is implemented.

Nam