fbdev/sisfb: Initialize fb_ops to fbdev I/O-memory helpers

Initialize the instance of struct fb_ops with fbdev initializer
macros for framebuffers in I/O address space. Set the read/write,
draw and mmap callbacks to the correct implementation and avoid
implicit defaults. Also select the necessary I/O helpers in Kconfig.

Fbdev drivers sometimes rely on the callbacks being NULL for a
default implementation to be invoked; hence requiring the I/O
helpers to be built in any case. Setting all callbacks in all
drivers explicitly will allow to make the I/O helpers optional.
This benefits systems that do not use these functions.

No functional changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230927074722.6197-36-tzimmermann@suse.de

drivers/video/fbdev/Kconfig

@@ -1203,10 +1203,11 @@ config FB_SAVAGE_ACCEL
 config FB_SIS
 	tristate "SiS/XGI display support"
 	depends on FB && PCI
+	select BOOT_VESA_SUPPORT if FB_SIS = y
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT
-	select BOOT_VESA_SUPPORT if FB_SIS = y
+	select FB_IOMEM_FOPS
 	select FB_SIS_300 if !FB_SIS_315
 	select VIDEO_NOMODESET
 	help

drivers/video/fbdev/sis/sis_main.c

@@ -1911,6 +1911,7 @@ static const struct fb_ops sisfb_ops = {
 	.owner		= THIS_MODULE,
 	.fb_open	= sisfb_open,
 	.fb_release	= sisfb_release,
+	__FB_DEFAULT_IOMEM_OPS_RDWR,
 	.fb_check_var	= sisfb_check_var,
 	.fb_set_par	= sisfb_set_par,
 	.fb_setcolreg	= sisfb_setcolreg,
@@ -1923,7 +1924,8 @@ static const struct fb_ops sisfb_ops = {
 #ifdef SIS_NEW_CONFIG_COMPAT
 	.fb_compat_ioctl= sisfb_ioctl,
 #endif
-	.fb_ioctl	= sisfb_ioctl
+	.fb_ioctl	= sisfb_ioctl,
+	__FB_DEFAULT_IOMEM_OPS_MMAP,
 };
 
 /* ---------------- Chip generation dependent routines ---------------- */