linux-kernel - Re: [PATCH 1/3] tty/vt: 8th bit location in vc

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Message-ID: <339029f2-1f54-40ea-8880-e68fbd351755@kernel.org>
Date: Sun, 31 Aug 2025 08:14:54 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Zsolt Kajtar <soci@....rulez.org>, linux-serial@...r.kernel.org,
 linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org
Subject: Re: [PATCH 1/3] tty/vt: 8th bit location in vc_uniscr routines

On 29. 08. 25, 21:49, Zsolt Kajtar wrote:
> Both vc_uniscr_check and vc_uniscr_copy_line assume that the 8th bit of
> glyph is also the 8th bit in the screen buffer. However this is only the
> case for fbcon at the moment. Vgacon has it on the 11th and so the
> conversion won't work correctly in that case. The patch corrects this
> oversight.
> 
> Signed-off-by: Zsolt Kajtar <soci@....rulez.org>
> ---
>   drivers/tty/vt/vt.c | 16 +++++++++++-----
>   1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 869261141..c6c931047 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -493,7 +493,7 @@ int vc_uniscr_check(struct vc_data *vc)
>   {
>   	u32 **uni_lines;
>   	unsigned short *p;
> -	int x, y, mask;
> +	int x, y;
>   
>   	WARN_CONSOLE_UNLOCKED();
>   
> @@ -514,11 +514,14 @@ int vc_uniscr_check(struct vc_data *vc)
>   	 * unicode content will be available after a complete screen refresh.
>   	 */
>   	p = (unsigned short *)vc->vc_origin;
> -	mask = vc->vc_hi_font_mask | 0xff;
>   	for (y = 0; y < vc->vc_rows; y++) {
>   		u32 *line = uni_lines[y];
>   		for (x = 0; x < vc->vc_cols; x++) {
> -			u16 glyph = scr_readw(p++) & mask;
> +			u16 w = scr_readw(p++);
> +			u16 glyph = w & 0xff;
> +
> +			if (w & vc->vc_hi_font_mask)
> +				glyph |= 0x100;

This makes sense, but introduce a helper, please.

>   			line[x] = inverse_translate(vc, glyph, true);
>   		}
>   	}
> @@ -561,10 +564,13 @@ void vc_uniscr_copy_line(const struct vc_data *vc, void *dest, bool viewed,
>   		 * buffer of its own.
>   		 */
>   		u16 *p = (u16 *)pos;
> -		int mask = vc->vc_hi_font_mask | 0xff;
>   		u32 *uni_buf = dest;
>   		while (nr--) {
> -			u16 glyph = scr_readw(p++) & mask;
> +			u16 w = scr_readw(p++);
> +			u16 glyph = w & 0xff;
> +
> +			if (w & vc->vc_hi_font_mask)
> +				glyph |= 0x100;

And use here as well.

>   			*uni_buf++ = inverse_translate(vc, glyph, true);
>   		}
>   	}


-- 
js
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