[PATCH] uvesafb: make scaling configurable on Nvidia cards

[ I sent this some times ago, but didn't get any response ]


Nvidia cards have a BIOS function 0x4f14 that allows to set flat panel
scaling. This patch adds a module parameter "scaling" that uses this
function to set the scaling. By default, the parameter is -1, so that the
driver doesn't attempt to call the scaling function.

This patch is useful when using the binary Nvidia graphics driver - in
that case, the console may be only in text mode or VESA mode. By default,
the video card does scaling that degrades font quality and changes aspect
ratio. This patch makes it possible to turn off the scaling and improve
font quality on the console.

The allowed values depend on VESA BIOS. On my card, the following values
are allowed:
-1	- do not change the scaling
0	- scale to full screen
1, 2	- don't scale
3	- scale and preserve aspect ratio
4	- scale with black border around

Example use:
echo 1 >/sys/module/uvesafb/parameters/scaling; fbset 1280x1024-60 -depth 32 -a
- this sets unscaled 1280x1024 video mode that has much sharper font than
  the scaled modes.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Index: linux-4.0.9/drivers/video/fbdev/uvesafb.c
=================================--- linux-4.0.9.orig/drivers/video/fbdev/uvesafb.c

+++ linux-4.0.9/drivers/video/fbdev/uvesafb.c

@@ -52,6 +52,7 @@ static u16 maxclk;		/* maximum pixel clo
 static u16 maxvf;		/* maximum vertical frequency */
 static u16 maxhf;		/* maximum horizontal frequency */
 static u16 vbemode;		/* force use of a specific VBE mode */
+static short scaling = -1;
 static char *mode_option;
 static u8  dac_width	= 6;
 

@@ -1245,7 +1246,22 @@ static int uvesafb_set_par(struct fb_inf
 	task = uvesafb_prep();
 	if (!task)
 		return -ENOMEM;
+
+	if (scaling > 0) {
+		/*
+		 * We must first reset scaling state with 0. This is workaround
+		 * for some supposed BIOS bug - without this, scaling mode 4
+		 * could not be set.
+		 */
+		uvesafb_reset(task);
+		task->t.regs.eax = 0x4f14;
+		task->t.regs.ebx = 0x0102;
+		task->t.regs.ecx = 0;
+		uvesafb_exec(task);
+	}
+
 setmode:
+	uvesafb_reset(task);
 	task->t.regs.eax = 0x4f02;
 	task->t.regs.ebx = mode->mode_id | 0x4000;	/* use LFB */
 

@@ -1296,7 +1312,6 @@ setmode:
 			printk(KERN_WARNING "uvesafb: mode switch failed "
 				"(eax=0x%x, err=%d). Trying again with "
 				"default timings.\n", task->t.regs.eax, err);
-			uvesafb_reset(task);
 			kfree(crtc);
 			crtc = NULL;
 			info->var.pixclock = 0;

@@ -1330,6 +1345,14 @@ setmode:
 				FB_VISUAL_PSEUDOCOLOR : FB_VISUAL_TRUECOLOR;
 	info->fix.line_length = mode->bytes_per_scan_line;
 
+	if (scaling >= 0) {
+		uvesafb_reset(task);
+		task->t.regs.eax = 0x4f14;
+		task->t.regs.ebx = 0x0102;
+		task->t.regs.ecx = scaling;
+		uvesafb_exec(task);
+	}
+
 out:
 	kfree(crtc);
 	uvesafb_free(task);

@@ -2019,6 +2042,9 @@ MODULE_PARM_DESC(vbemode,
 	"VBE mode number to set, overrides the 'mode' option");
 module_param_string(v86d, v86d_path, PATH_MAX, 0660);
 MODULE_PARM_DESC(v86d, "Path to the v86d userspace helper.");
+module_param(scaling, short, 0660);
+MODULE_PARM_DESC(scaling,
+	"Scaling option for nvidia (0 - scaled, 1 - unscaled centered, 2 - unscaled in left corner");
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Michal Januszewski <spock@gentoo.org>");

Index: linux-4.0.9/Documentation/fb/uvesafb.txt
=================================--- linux-4.0.9.orig/Documentation/fb/uvesafb.txt

+++ linux-4.0.9/Documentation/fb/uvesafb.txt

@@ -128,6 +128,14 @@ v86d:path
         need to use it and have uvesafb built into the kernel, use
         uvesafb.v86d="path".
 
+scaling:n
+	Set scaling on Nvidia cards. Possible values depend on card's BIOS.
+		-1	- do not change the scaling
+		0	- scale to full screen
+		1, 2	- don't scale
+		3	- scale and preserve aspect ratio
+		4	- scale with black border around
+
 Additionally, the following parameters may be provided.  They all override the
 EDID-provided values and BIOS defaults.  Refer to your monitor's specs to get
 the correct values for maxhf, maxvf and maxclk for your hardware.

On 03/09/15 00:23, Mikulas Patocka wrote:

[ I sent this some times ago, but didn't get any response ]


Nvidia cards have a BIOS function 0x4f14 that allows to set flat panel
scaling. This patch adds a module parameter "scaling" that uses this
function to set the scaling. By default, the parameter is -1, so that the
driver doesn't attempt to call the scaling function.

This patch is useful when using the binary Nvidia graphics driver - in
that case, the console may be only in text mode or VESA mode. By default,
the video card does scaling that degrades font quality and changes aspect
ratio. This patch makes it possible to turn off the scaling and improve
font quality on the console.

The allowed values depend on VESA BIOS. On my card, the following values
are allowed:
-1	- do not change the scaling
0	- scale to full screen
1, 2	- don't scale
3	- scale and preserve aspect ratio
4	- scale with black border around

Example use:
echo 1 >/sys/module/uvesafb/parameters/scaling; fbset 1280x1024-60 -depth 32 -a
- this sets unscaled 1280x1024 video mode that has much sharper font than
  the scaled modes.

I have to say I don't know much about x86 video, but isn't uvesafb
supposed to be a generic driver? Adding nvidia specific features there
doesn't sound like a right way to handle this.

 Tomi

On Thu, 8 Oct 2015, Tomi Valkeinen wrote:

On 03/09/15 00:23, Mikulas Patocka wrote:

quoted

[ I sent this some times ago, but didn't get any response ]


Nvidia cards have a BIOS function 0x4f14 that allows to set flat panel
scaling. This patch adds a module parameter "scaling" that uses this
function to set the scaling. By default, the parameter is -1, so that the
driver doesn't attempt to call the scaling function.

This patch is useful when using the binary Nvidia graphics driver - in
that case, the console may be only in text mode or VESA mode. By default,
the video card does scaling that degrades font quality and changes aspect
ratio. This patch makes it possible to turn off the scaling and improve
font quality on the console.

The allowed values depend on VESA BIOS. On my card, the following values
are allowed:
-1	- do not change the scaling
0	- scale to full screen
1, 2	- don't scale
3	- scale and preserve aspect ratio
4	- scale with black border around

Example use:
echo 1 >/sys/module/uvesafb/parameters/scaling; fbset 1280x1024-60 -depth 32 -a
- this sets unscaled 1280x1024 video mode that has much sharper font than
  the scaled modes.

I have to say I don't know much about x86 video, but isn't uvesafb
supposed to be a generic driver? Adding nvidia specific features there
doesn't sound like a right way to handle this.

 Tomi

Where do you think that this functionality should be added? To Nouveau? - 
Nouveau can't be used with nVidia binary driver, and this functionality is 
useful especially with nVidia binary driver (it allows to get nice console 
with sharp fonts).

BTW. I don't know if this BIOS function is supported on AMD or not. Could 
someone try it? I don't have an AMD card.

Mikulas

On 08/10/15 14:51, Mikulas Patocka wrote:

quoted

I have to say I don't know much about x86 video, but isn't uvesafb
supposed to be a generic driver? Adding nvidia specific features there
doesn't sound like a right way to handle this.

 Tomi

Where do you think that this functionality should be added? To Nouveau? - 
Nouveau can't be used with nVidia binary driver, and this functionality is 
useful especially with nVidia binary driver (it allows to get nice console 
with sharp fonts).

I don't know where is should be. But with a quick look I don't see any
gfx card specific features in uvesafb, and the doc clearly says it's a
generic driver. So if we add this nvidia feature there, shall we add
other features for other cards also? It's a kind of slippery road.

So how does uvesafb work with nvidia driver? uvesafb is used for initial
console, and nvidia driver takes over later when (and if) it's loaded?
And it's not possible to change the scaling via nvidia's driver?

BTW. I don't know if this BIOS function is supported on AMD or not. Could 
someone try it? I don't have an AMD card.

Quick googling shows that 0x4f14 might be used by other gfx cards (Epia)
for something else. But I can't really say for sure. So in the minimum I
think the parameter should be renamed to "nvidia_scaling" or similar.

 Tomi

On Thu, 8 Oct 2015, Tomi Valkeinen wrote:

On 08/10/15 14:51, Mikulas Patocka wrote:

quoted

quoted

I have to say I don't know much about x86 video, but isn't uvesafb
supposed to be a generic driver? Adding nvidia specific features there
doesn't sound like a right way to handle this.

 Tomi

Where do you think that this functionality should be added? To Nouveau? - 
Nouveau can't be used with nVidia binary driver, and this functionality is 
useful especially with nVidia binary driver (it allows to get nice console 
with sharp fonts).

I don't know where is should be. But with a quick look I don't see any
gfx card specific features in uvesafb, and the doc clearly says it's a
generic driver. So if we add this nvidia feature there, shall we add
other features for other cards also? It's a kind of slippery road.

So how does uvesafb work with nvidia driver? uvesafb is used for initial
console, and nvidia driver takes over later when (and if) it's loaded?
And it's not possible to change the scaling via nvidia's driver?

The nvidia binary driver doesn't handle console, it only handles Xwindow. 
You can use either the VGA 80x25 text console or you can set graphics 
console with uvesafb - in both cases, the video card hardware scales the 
screen and the console font is blurry. The patch allows to turn off the 
scaling.

quoted

BTW. I don't know if this BIOS function is supported on AMD or not. Could 
someone try it? I don't have an AMD card.

Quick googling shows that 0x4f14 might be used by other gfx cards (Epia)
for something else. But I can't really say for sure. So in the minimum I
think the parameter should be renamed to "nvidia_scaling" or similar.

Someone should try the patch on AMD card and say if it can set scaling 
there.

Mikulas

 Tomi