viafb: add X server compatibility mode

This patch adds a config option to be compatible with X servers like
OpenChrome. This is required as for example the X server does not
handle things like disabled IGAs/PLLs resulting in a potential
freeze on X startup. With this option disabled we can provide some
nice features like power management and not reinitializing the
hardware on every mode switch (taking long time, causing flickering).
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>

drivers/video/Kconfig

@@ -1607,6 +1607,17 @@ config FB_VIA_DIRECT_PROCFS
 	  correct output device configuration.
 	  Its use is strongly discouraged.
 
+config FB_VIA_X_COMPATIBILITY
+	bool "X server compatibility"
+	depends on FB_VIA
+	default n
+	help
+	  This option reduces the functionality (power saving, ...) of the
+	  framebuffer to avoid negative impact on the OpenChrome X server.
+	  If you use any X server other than fbdev you should enable this
+	  otherwise it should be safe to disable it and allow using all
+	  features.
+
 endif
 
 config FB_NEOMAGIC

drivers/video/via/hw.c

@@ -2293,6 +2293,12 @@ int viafb_setmode(struct VideoModeTable *vmode_tbl, int video_bpp,
 	clock.set_primary_clock_source(VIA_CLKSRC_X1, true);
 	clock.set_secondary_clock_source(VIA_CLKSRC_X1, true);
 
+#ifdef CONFIG_FB_VIA_X_COMPATIBILITY
+	clock.set_primary_pll_state(VIA_STATE_ON);
+	clock.set_primary_clock_state(VIA_STATE_ON);
+	clock.set_secondary_pll_state(VIA_STATE_ON);
+	clock.set_secondary_clock_state(VIA_STATE_ON);
+#else
 	if (viaparinfo->shared->iga1_devices) {
 		clock.set_primary_pll_state(VIA_STATE_ON);
 		clock.set_primary_clock_state(VIA_STATE_ON);
@@ -2308,6 +2314,7 @@ int viafb_setmode(struct VideoModeTable *vmode_tbl, int video_bpp,
 		clock.set_secondary_pll_state(VIA_STATE_OFF);
 		clock.set_secondary_clock_state(VIA_STATE_OFF);
 	}
+#endif /*CONFIG_FB_VIA_X_COMPATIBILITY*/
 
 	via_set_state(devices, VIA_STATE_ON);
 	device_screen_on();