[U-Boot] [PATCH 1/2] efi_loader: cursor positioning

[Alexander Graf]

On 05.09.19 10:06, Heinrich Schuchardt wrote:
> When backspacing in column 0 do no set the column index to ULONG_MAX.
> Ensure that the row number is not set to ULONG_MAX even if the row count is
> advertised as 0.
> Ignore control characters other the 0x08, 0x0a, 0x0d when updating the
> column.
>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
> ---
>   lib/efi_loader/efi_console.c | 12 ++++++++----
>   1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/lib/efi_loader/efi_console.c b/lib/efi_loader/efi_console.c
> index d4765afb98..d5222c46b4 100644
> --- a/lib/efi_loader/efi_console.c
> +++ b/lib/efi_loader/efi_console.c
> @@ -156,13 +156,14 @@ static efi_status_t EFIAPI efi_cout_output_string(
>   	 * Update the cursor position.
>   	 *
>   	 * The UEFI spec provides advance rules for U+0000, U+0008, U+000A,
> -	 * and U000D. All other characters, including control characters
> -	 * U+0007 (BEL) and U+0009 (TAB), have to increase the column by one.
> +	 * and U000D. All other control characters are ignored. Any non-control
> +	 * character increase the column by one.
>   	 */
>   	for (p = string; *p; ++p) {
>   		switch (*p) {
>   		case '\b':	/* U+0008, backspace */
> -			con->cursor_column = max(0, con->cursor_column - 1);
> +			if (con->cursor_column)
> +				con->cursor_column--;
>   			break;
>   		case '\n':	/* U+000A, newline */
>   			con->cursor_column = 0;
> @@ -178,13 +179,16 @@ static efi_status_t EFIAPI efi_cout_output_string(
>   			 */
>   			break;
>   		default:
> -			con->cursor_column++;
> +			if (*p > 0x1f)


What is the 0x1f here? I know, control character, but it's not obvious. 
Probably wants either a comment or a define.


> +				con->cursor_column++;
>   			break;
>   		}
>   		if (con->cursor_column >= mode->columns) {
>   			con->cursor_column = 0;
>   			con->cursor_row++;
>   		}
> +		if (con->cursor_row >= mode->rows && con->cursor_row)
> +			con->cursor_row--;


I don't understand this statement. When is the cursor_row >= mode->rows? 
Is this just to offset an incorrect cursor_row from the line above? 
Can't we just fold it in there?


Alex