Re: [PATCH 2/2] vt: Distinguish between blanking and VESA blank mode in con_blank

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 12.10.26 um 13:29 schrieb Greg KH:
> On Mon, Oct 12, 2026 at 11:27:39AM +0200, Thomas Zimmermann wrote:
>> The con_blank callback in struct consw encodes blanking and display
>> blank mode in a single parameter named blank. Its semantics equal
>> the FB_BLANK constants from the fbdev subsystems. Yet it is of type
>> enum vesa_blank_mode, which describes VESA DPMS levels of the attached
>> monitor. Although related, this is something else.
>>
>> For this reason, calls to con_blank fill the blank parameter with
>> values that appear non-sensical at first. For example, to blank the
>> console, but keep the monitor on, vt passes VESA_VSYNC_SUSPEND (eq '1').
>> This is because consoles interpret '1' as pixels-off-but-monitor-on.
>> The constant VESA_VSYNC_SUSPEND actually means monitor-vsync-off. And
>> the argument used for monitor-vsync-off is VESA_VSYNC_SUSPEND+1.
>>
>> To fix this by splitting blank into two parameters, blank and blank_mode.
>> The new blank is a boolean to control the display blanking. If cleared,
>> the console creates display output, if set the console does not. The
>> new parameter blank_mode specifies the VESA blank mode for the monitor
>> and equals VESA DPMS levels. If blank is set, blank_mode gives a hint
>> to the console, on how to set up the signal to the monitor.
>>
>> The actual interpretation is up to the console. Newportcon and sticon
>> only handle blank or not-blank. Fbcon and vgacon implement blank plus
>> the VESA DPMS handling. The implementation of both consoles is again
>> somewhat confusing because types and values do not match. Clean up
>> both with the new blank/blank_mode logic.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> ---
>>   drivers/tty/vt/vt.c                 | 11 ++++----
>>   drivers/video/console/dummycon.c    |  4 +--
>>   drivers/video/console/newport_con.c |  4 +--
>>   drivers/video/console/sticon.c      |  4 +--
>>   drivers/video/console/vgacon.c      | 44 +++++++++++++++--------------
>>   drivers/video/fbdev/core/fbcon.c    | 19 +++++++------
>>   include/linux/console.h             |  9 ++++--
>>   7 files changed, 51 insertions(+), 44 deletions(-)
>>
>> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
>> index 9e7b4419b422..f762c965351d 100644
>> --- a/drivers/tty/vt/vt.c
>> +++ b/drivers/tty/vt/vt.c
>> @@ -4671,7 +4671,7 @@ void do_blank_screen(bool entering_gfx)
>>   	if (console_blanked) {
>>   		if (blank_state == blank_vesa_wait) {
>>   			blank_state = blank_off;
>> -			vc->vc_sw->con_blank(vc, vesa_blank_mode + 1, false);
>> +			vc->vc_sw->con_blank(vc, true, vesa_blank_mode, false);
> I hate adding random bool to function parameters as now you need to go
> look them up to try to determine exactly what happened.
>
> Why not just 2 different callbacks:

Sounds like a cleaner design.


>
>> -static bool vgacon_blank(struct vc_data *c, enum vesa_blank_mode blank,
>> +static bool vgacon_blank(struct vc_data *c, bool blank, enum vesa_blank_mode blank_mode,
>>   			 bool mode_switch)
>>   {
>> -	switch (blank) {
>> -	case VESA_NO_BLANKING:		/* Unblank */
>> +	if (blank) {
>> +		switch (blank_mode) {
>> +		case VESA_NO_BLANKING:	/* Normal blanking */
>> +			if (!mode_switch && vga_video_type == VIDEO_TYPE_VGAC) {
>> +				vga_pal_blank(&vgastate);
>> +				vga_palette_blanked = true;
>> +				return 0;
>> +			}
>> +			vgacon_set_origin(c);
>> +			scr_memsetw((void *)vga_vram_base, BLANK,
>> +				    c->vc_screenbuf_size);
>> +			if (mode_switch)
>> +				vga_is_gfx = true;
>> +			return 1;
>> +		default:		/* VESA blanking */
>> +			if (vga_video_type == VIDEO_TYPE_VGAC) {
>> +				vga_vesa_blank(&vgastate, blank_mode);
>> +				vga_vesa_blanked = blank_mode;
>> +			}
>> +			return 0;
>> +		}
>> +	} else { /* Unblank */
>>   		if (vga_vesa_blanked) {
>>   			vga_vesa_unblank(&vgastate);
>>   			vga_vesa_blanked = VESA_NO_BLANKING;
>> @@ -814,24 +834,6 @@ static bool vgacon_blank(struct vc_data *c, enum vesa_blank_mode blank,
>>   		vga_is_gfx = false;
>>   		/* Tell console.c that it has to restore the screen itself */
>>   		return 1;
>> -	case VESA_VSYNC_SUSPEND:	/* Normal blanking */
>> -		if (!mode_switch && vga_video_type == VIDEO_TYPE_VGAC) {
>> -			vga_pal_blank(&vgastate);
>> -			vga_palette_blanked = true;
>> -			return 0;
>> -		}
>> -		vgacon_set_origin(c);
>> -		scr_memsetw((void *) vga_vram_base, BLANK,
>> -			    c->vc_screenbuf_size);
>> -		if (mode_switch)
>> -			vga_is_gfx = true;
>> -		return 1;
>> -	default:		/* VESA blanking */
>> -		if (vga_video_type == VIDEO_TYPE_VGAC) {
>> -			vga_vesa_blank(&vgastate, blank - 1);
>> -			vga_vesa_blanked = blank;
>> -		}
>> -		return 0;
>>   	}
> This can be vgacon_blank() and vgacon_unblank(), right?  That way we
> have a hint as to what is happening and don't have to try to remember
> that a bool as parameter 2 is blank/unblank.

Yeah, we can do that.  We'd also not need the VESA mode in the unblank 
case. It's always VESA_NO_BLANKING there.

Best regards
Thomas

>
> thanks,
>
> greg k-h
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)