linux-kernel - Re: [PATCH 3/3] tty/vt: Fix unreadable kernel messages on vgacon

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Message-ID: <cd96426e-c1e0-4229-be72-feacacf5962b@kernel.org>
Date: Sun, 31 Aug 2025 08:28:35 +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 3/3] tty/vt: Fix unreadable kernel messages on vgacon

On 29. 08. 25, 21:49, Zsolt Kajtar wrote:
> When a 512 glyph font is loaded on vgacon and the bold attributes are in
> effect then the kernel console output (printk) becomes unreadable. It is
> because the brightness bit (used for bold) is at the same place where
> the 8th bit of the glyph index is. This patch adds the missing masking
> to ensure the output will be displayed using the lower half of the font.
> 
> Signed-off-by: Zsolt Kajtar <soci@....rulez.org>

Reviewed-by: Jiri Slaby <jirislaby@...nel.org>

I assume you checked all writes to the gfx mem?

> ---
>   drivers/tty/vt/vt.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index d54f4d24e..4c8c87f21 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -3356,7 +3356,8 @@ static void vt_console_print(struct console *co, const char *b, unsigned count)
>   				continue;
>   		}
>   		vc_uniscr_putc(vc, c);
> -		scr_writew((vc->vc_attr << 8) + c, (unsigned short *)vc->vc_pos);
> +		scr_writew(((vc->vc_attr << 8) & ~vc->vc_hi_font_mask) | c,
> +			   (unsigned short *)vc->vc_pos);
>   		notify_write(vc, c);
>   		cnt++;
>   		if (vc->state.x == vc->vc_cols - 1) {


-- 
js
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