[media] r820t: Add a tuner driver for Rafael Micro R820T silicon tuner

This driver was written from scratch, based on an existing driver
that it is part of rtl-sdr git tree, released under GPLv2:
	https://groups.google.com/forum/#!topic/ultra-cheap-sdr/Y3rBEOFtHug
	https://github.com/n1gp/gr-baz
	http://cgit.osmocom.org/rtl-sdr/plain/src/tuner_r820t.c
	(there are also other variants of it out there)
>From what I understood from the threads, the original driver was converted
to userspace from a Realtek tree. I couldn't find the original tree.
However, the original driver look awkward on my eyes. So, I decided to
write a new version from it from the scratch, while trying to reproduce
everything found there.
TODO:
- After locking, the original driver seems to have some routines to
  improve reception. This was not implemented here yet.
- RF Gain set/get is not implemented.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Tested-by: Antti Palosaari <crope@iki.fi>

drivers/media/tuners/Kconfig

@@ -248,4 +248,11 @@ config MEDIA_TUNER_IT913X
 	default m if !MEDIA_SUBDRV_AUTOSELECT
 	help
 	  ITE Tech IT913x silicon tuner driver.
+
+config MEDIA_TUNER_R820T
+	tristate "Rafael Micro R820T silicon tuner"
+	depends on MEDIA_SUPPORT && I2C
+	default m if !MEDIA_SUBDRV_AUTOSELECT
+	help
+	  Rafael Micro R820T silicon tuner driver.
 endmenu

drivers/media/tuners/Makefile

@@ -35,6 +35,7 @@ obj-$(CONFIG_MEDIA_TUNER_FC0011) += fc0011.o
 obj-$(CONFIG_MEDIA_TUNER_FC0012) += fc0012.o
 obj-$(CONFIG_MEDIA_TUNER_FC0013) += fc0013.o
 obj-$(CONFIG_MEDIA_TUNER_IT913X) += tuner_it913x.o
+obj-$(CONFIG_MEDIA_TUNER_R820T) += r820t.o
 
 ccflags-y += -I$(srctree)/drivers/media/dvb-core
 ccflags-y += -I$(srctree)/drivers/media/dvb-frontends

drivers/media/tuners/r820t.h

@@ -0,0 +1,55 @@
+/*
+ * Elonics R820T silicon tuner driver
+ *
+ * Copyright (C) 2012 Antti Palosaari <crope@iki.fi>
+ *
+ *    This program is free software; you can redistribute it and/or modify
+ *    it under the terms of the GNU General Public License as published by
+ *    the Free Software Foundation; either version 2 of the License, or
+ *    (at your option) any later version.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU General Public License for more details.
+ *
+ *    You should have received a copy of the GNU General Public License along
+ *    with this program; if not, write to the Free Software Foundation, Inc.,
+ *    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef R820T_H
+#define R820T_H
+
+#include <linux/kconfig.h>
+#include "dvb_frontend.h"
+
+enum r820t_chip {
+	CHIP_R820T,
+	CHIP_R828S,
+	CHIP_R820C,
+};
+
+struct r820t_config {
+	u8 i2c_addr;		/* 0x34 */
+
+	u32 xtal;
+	enum r820t_chip rafael_chip;
+	unsigned max_i2c_msg_len;
+};
+
+#if IS_ENABLED(CONFIG_MEDIA_TUNER_R820T)
+struct dvb_frontend *r820t_attach(struct dvb_frontend *fe,
+				  struct i2c_adapter *i2c,
+				  const struct r820t_config *cfg);
+#else
+static inline struct dvb_frontend *r820t_attach(struct dvb_frontend *fe,
+						struct i2c_adapter *i2c,
+						const struct r820t_config *cfg)
+{
+	pr_warn("%s: driver disabled by Kconfig\n", __func__);
+	return NULL;
+}
+#endif
+
+#endif