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

[Nam Cao <namcaov@gmail.com>]

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