V4L/DVB (10392): lnbp21: documentation about the system register

Here is a patch which adds some documentation about meanings of the
the lnbp21 system register bits.
Signed-off-by: Hans Werner <hwerner4@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/dvb/frontends/lnbp21.h

@@ -28,14 +28,14 @@
 #define _LNBP21_H
 
 /* system register bits */
-#define LNBP21_OLF	0x01
-#define LNBP21_OTF	0x02
-#define LNBP21_EN	0x04
-#define LNBP21_VSEL	0x08
-#define LNBP21_LLC	0x10
-#define LNBP21_TEN	0x20
-#define LNBP21_ISEL	0x40
-#define LNBP21_PCL	0x80
+#define LNBP21_OLF     0x01 /* [R-only] 0=OK; 1=over current limit flag*/
+#define LNBP21_OTF     0x02 /* [R-only] 0=OK; 1=over temperature flag (150degC typ) */
+#define LNBP21_EN      0x04 /* [RW] 0=disable LNB power, enable loopthrough; 1=enable LNB power, disable loopthrough*/
+#define LNBP21_VSEL    0x08 /* [RW] 0=low voltage (13/14V, vert pol); 1=high voltage (18/19V,horiz pol) */
+#define LNBP21_LLC     0x10 /* [RW] increase LNB voltage by 1V:  0=13/18V; 1=14/19V */
+#define LNBP21_TEN     0x20 /* [RW] 0=tone controlled by DSQIN pin; 1=tone enable, disable DSQIN */
+#define LNBP21_ISEL    0x40 /* [RW] current limit select 0:Iout=500-650mA,Isc=300mA ; 1:Iout=400-550mA,Isc=200mA*/
+#define LNBP21_PCL     0x80 /* [RW] short-circuit prot: 0=pulsed (dynamic) curr limiting; 1=static curr limiting*/
 
 #include <linux/dvb/frontend.h>