fbdev: Add fb_ops init macros for framebuffers in DMA-able memory

Add initializer macros for struct fb_ops for framebuffers in DMA-able
memory areas. Also add a corresponding Kconfig token. As of now, this
is equivalent to system framebuffers and mostly useful for labeling
drivers correctly.

A later patch may add a generic DMA-specific mmap operation. Linux
offers a number of dma_mmap_*() helpers for different use cases.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230707083422.18691-2-tzimmermann@suse.de

drivers/video/fbdev/core/Kconfig

@@ -136,6 +136,14 @@ config FB_DEFERRED_IO
 	bool
 	depends on FB_CORE
 
+config FB_DMA_HELPERS
+	bool
+	depends on FB_CORE
+	select FB_SYS_COPYAREA
+	select FB_SYS_FILLRECT
+	select FB_SYS_FOPS
+	select FB_SYS_IMAGEBLIT
+
 config FB_IO_HELPERS
 	bool
 	depends on FB_CORE

include/linux/fb.h

@@ -591,6 +591,19 @@ extern ssize_t fb_sys_write(struct fb_info *info, const char __user *buf,
 	__FB_DEFAULT_SYS_OPS_DRAW, \
 	__FB_DEFAULT_SYS_OPS_MMAP
 
+/*
+ * Helpers for framebuffers in DMA-able memory
+ */
+
+#define __FB_DEFAULT_DMA_OPS_RDWR \
+	.fb_read	= fb_sys_read, \
+	.fb_write	= fb_sys_write
+
+#define __FB_DEFAULT_DMA_OPS_DRAW \
+	.fb_fillrect	= sys_fillrect, \
+	.fb_copyarea	= sys_copyarea, \
+	.fb_imageblit	= sys_imageblit
+
 /* drivers/video/fbmem.c */
 extern int register_framebuffer(struct fb_info *fb_info);
 extern void unregister_framebuffer(struct fb_info *fb_info);