[PATCH] neofb: avoid resetting display config on unblank (v2)

There were two mistakes in the register-read-on-(un)blank approach.

- First, without proper register (un)locking the value read back will always
  be zero, and this is what I missed entirely until just now.  Due to this,
  the logic could not be verified at all and I tried some bogus checks which
  are completely stupid.

- Second, the LCD status bit will always be set to zero when the backlight
  has been turned off.  Reading the value back during unblank will disable the
  LCD unconditionally, regardless of the state it is supposed to be in, since
  we set it to zero beforehand.

So this is what we do now:

- create a new variable in struct neofb_par, and use that to determine
  whether to read back registers (initialized to true)

- before actually blanking the screen, read back the register to sense any
  possible change made through Fn key combo

- use proper neoUnlock() / neoLock() to actually read something

- every call to neofb_blank() determines if we read back next time: blanking
  disables readback, unblanking (FB_BLANK_UNBLANK) enables it

This should give us a nice and clean state machine.  Has been thoroughly
tested on a Dell Latitude CPiA / NM220 Chip docked to a C/Dock2 with attached
CRT in all possible combinations of LCD/CRT on/off.  I changed the config via
Fn key, let the console blank, unblanked by keypress - works flawlessly.
Signed-off-by: NChristian Trefzer <ctrefzer@gmx.de>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

drivers/video/neofb.c

@@ -843,6 +843,9 @@ static int neofb_set_par(struct fb_info *info)
 
 	par->SysIfaceCntl2 = 0xc0;	/* VESA Bios sets this to 0x80! */
 
+	/* Initialize: by default, we want display config register to be read */
+	par->PanelDispCntlRegRead = 1;
+
 	/* Enable any user specified display devices. */
 	par->PanelDispCntlReg1 = 0x00;
 	if (par->internal_display)
@@ -1334,11 +1337,17 @@ static int neofb_blank(int blank_mode, struct fb_info *info)
 	struct neofb_par *par = info->par;
 	int seqflags, lcdflags, dpmsflags, reg;
 
+
 	/*
-	 * Reload the value stored in the register, might have been changed via
-	 * FN keystroke
+	 * Reload the value stored in the register, if sensible. It might have
+	 * been changed via FN keystroke.
 	 */
-	par->PanelDispCntlReg1 = vga_rgfx(NULL, 0x20) & 0x03;
+	if (par->PanelDispCntlRegRead) {
+		neoUnlock();
+		par->PanelDispCntlReg1 = vga_rgfx(NULL, 0x20) & 0x03;
+		neoLock(&par->state);
+	}
+	par->PanelDispCntlRegRead = !blank_mode;
 
 	switch (blank_mode) {
 	case FB_BLANK_POWERDOWN:	/* powerdown - both sync lines down */

include/video/neomagic.h

@@ -159,6 +159,7 @@ struct neofb_par {
 	unsigned char PanelDispCntlReg1;
 	unsigned char PanelDispCntlReg2;
 	unsigned char PanelDispCntlReg3;
+	unsigned char PanelDispCntlRegRead;
 	unsigned char PanelVertCenterReg1;
 	unsigned char PanelVertCenterReg2;
 	unsigned char PanelVertCenterReg3;