[media] em28xx: introduce #define for maximum supported scaling values (register 0x30-0x33)

The maximum supported scaling value for registers 0x30+0x31 (horizontal scaling)
and 0x32+0x33 (vertical scaling) is 0x3fff, which corresponds to 20% of the
input frame size.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/usb/em28xx/em28xx-reg.h

@@ -152,6 +152,8 @@
 #define EM28XX_R31_HSCALEHIGH	0x31
 #define EM28XX_R32_VSCALELOW	0x32
 #define EM28XX_R33_VSCALEHIGH	0x33
+#define   EM28XX_HVSCALE_MAX	0x3fff /* => 20% */
+
 #define EM28XX_R34_VBI_START_H	0x34
 #define EM28XX_R35_VBI_START_V	0x35
 #define EM28XX_R36_VBI_WIDTH	0x36

drivers/media/usb/em28xx/em28xx-video.c

@@ -807,12 +807,12 @@ static void get_scale(struct em28xx *dev,
 	unsigned int          maxh = norm_maxh(dev);
 
 	*hscale = (((unsigned long)maxw) << 12) / width - 4096L;
-	if (*hscale >= 0x4000)
-		*hscale = 0x3fff;
+	if (*hscale > EM28XX_HVSCALE_MAX)
+		*hscale = EM28XX_HVSCALE_MAX;
 
 	*vscale = (((unsigned long)maxh) << 12) / height - 4096L;
-	if (*vscale >= 0x4000)
-		*vscale = 0x3fff;
+	if (*vscale > EM28XX_HVSCALE_MAX)
+		*vscale = EM28XX_HVSCALE_MAX;
 }
 
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