video: fbdev: controlfb: add COMPILE_TEST support

Add COMPILE_TEST support to controlfb driver for better compile
testing coverage.

While at it:
- convert driver to use eieio() and dcbf() helpers instead of
  open-coding them
- add invalid_vram_cache() helper to avoid code duplication
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200324134508.25120-3-b.zolnierkie@samsung.com

drivers/video/fbdev/Kconfig

@@ -472,7 +472,7 @@ config FB_OF
 
 config FB_CONTROL
 	bool "Apple \"control\" display support"
-	depends on (FB = y) && PPC_PMAC && PPC32
+	depends on (FB = y) && ((PPC_PMAC && PPC32) || COMPILE_TEST)
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT

drivers/video/fbdev/controlfb.c

@@ -48,12 +48,37 @@
 #include <linux/nvram.h>
 #include <linux/adb.h>
 #include <linux/cuda.h>
+#ifdef CONFIG_PPC_PMAC
 #include <asm/prom.h>
 #include <asm/btext.h>
+#endif
 
 #include "macmodes.h"
 #include "controlfb.h"
 
+#ifndef CONFIG_PPC_PMAC
+#define invalid_vram_cache(addr)
+#undef in_8
+#undef out_8
+#undef in_le32
+#undef out_le32
+#define in_8(addr)		0
+#define out_8(addr, val)
+#define in_le32(addr)		0
+#define out_le32(addr, val)
+#define pgprot_cached_wthru(prot) (prot)
+#else
+static void invalid_vram_cache(void __force *addr)
+{
+	eieio();
+	dcbf(addr);
+	mb();
+	eieio();
+	dcbf(addr);
+	mb();
+}
+#endif
+
 struct fb_par_control {
 	int	vmode, cmode;
 	int	xres, yres;
@@ -309,7 +334,7 @@ static int controlfb_mmap(struct fb_info *info,
 
 static int controlfb_blank(int blank_mode, struct fb_info *info)
 {
-	struct fb_info_control *p =
+	struct fb_info_control __maybe_unused *p =
 		container_of(info, struct fb_info_control, info);
 	unsigned ctrl;
 
@@ -605,12 +630,7 @@ static void __init find_vram_size(struct fb_info_control *p)
 
 	out_8(&p->frame_buffer[0x600000], 0xb3);
 	out_8(&p->frame_buffer[0x600001], 0x71);
-	asm volatile("eieio; dcbf 0,%0" : : "r" (&p->frame_buffer[0x600000])
-					: "memory" );
-	mb();
-	asm volatile("eieio; dcbi 0,%0" : : "r" (&p->frame_buffer[0x600000])
-					: "memory" );
-	mb();
+	invalid_vram_cache(&p->frame_buffer[0x600000]);
 
 	bank2 = (in_8(&p->frame_buffer[0x600000]) == 0xb3)
 		&& (in_8(&p->frame_buffer[0x600001]) == 0x71);
@@ -624,12 +644,7 @@ static void __init find_vram_size(struct fb_info_control *p)
 
 	out_8(&p->frame_buffer[0], 0x5a);
 	out_8(&p->frame_buffer[1], 0xc7);
-	asm volatile("eieio; dcbf 0,%0" : : "r" (&p->frame_buffer[0])
-					: "memory" );
-	mb();
-	asm volatile("eieio; dcbi 0,%0" : : "r" (&p->frame_buffer[0])
-					: "memory" );
-	mb();
+	invalid_vram_cache(&p->frame_buffer[0]);
 
 	bank1 = (in_8(&p->frame_buffer[0]) == 0x5a)
 		&& (in_8(&p->frame_buffer[1]) == 0xc7);