This patch fixes the following error messages with a
Terratec Cinergy T Stick Dual RC DVB-T device.

af9013: i2c wr failed=-1 reg=d607 len=1
af9015: command failed:2
af9013: i2c rd failed=-1 reg=d607 len=1
af9015: command failed:1

It implements exclusive access to i2c for only one frontend at a time
through a use-counter that is increased for each af9013_i2c_gate_ctrl-enable
or i2c-read/write and decreased accordingly. The use-counter remains
incremented after af9013_i2c_gate_ctrl-enable until the corresponding
disable.

Debug output was added.

ToDo:
 * Replace frontend by adapter (the dual-tuner devices do actually
   provide two adapters with one frontend each)
 * move af9013_i2c_gate_mutex, locked_fe, af9013_i2c_gate_ctrl_usecnt
   to the usb device
---
 drivers/media/dvb/frontends/af9013.c |   93 +++++++++++++++++++++++++++++-----
 1 files changed, 80 insertions(+), 13 deletions(-)

diff --git a/drivers/media/dvb/frontends/af9013.c 
b/drivers/media/dvb/frontends/af9013.c
index 6bcbcf5..ab69585 100644
--- a/drivers/media/dvb/frontends/af9013.c
+++ b/drivers/media/dvb/frontends/af9013.c
@@ -28,6 +28,54 @@ int af9013_debug;
 module_param_named(debug, af9013_debug, int, 0644);
 MODULE_PARM_DESC(debug, "Turn on/off frontend debugging (default:off).");
 
+static DEFINE_MUTEX(af9013_i2c_gate_mutex);
+static struct dvb_frontend *locked_fe = 0;
+static int af9013_i2c_gate_ctrl_usecnt = 0;
+
+#define GATE_NOOP    0
+#define GATE_ENABLE  1
+#define GATE_DISABLE 2
+
+static int af9013_i2c_gate_inc_use_count(struct dvb_frontend *fe, int gate_op)
+{
+       int success = 0;
+       while (1) {
+               if (mutex_lock_interruptible(&af9013_i2c_gate_mutex) != 0) {
+                       return -EAGAIN;
+               }
+               if (af9013_i2c_gate_ctrl_usecnt == 0 || locked_fe == fe) {
+                       success = 1;
+                       locked_fe = fe;
+                       if (gate_op != GATE_DISABLE) {
+                               af9013_i2c_gate_ctrl_usecnt++;
+                       }
+               }
+               mutex_unlock(&af9013_i2c_gate_mutex);
+               if (success) {
+                       break;
+               }
+               schedule();
+       }
+       dbg("%s: %d (%d)", __func__, af9013_i2c_gate_ctrl_usecnt, fe->dvb->num);
+       return 0;
+}
+
+static int af9013_i2c_gate_dec_use_count(struct dvb_frontend *fe, int gate_op)
+{
+       if (mutex_lock_interruptible(&af9013_i2c_gate_mutex) != 0) {
+               return -EAGAIN;
+       }
+       if (gate_op != GATE_ENABLE) {
+               af9013_i2c_gate_ctrl_usecnt--;
+       }
+       if (af9013_i2c_gate_ctrl_usecnt == 0) {
+               locked_fe = 0;
+       }
+       mutex_unlock(&af9013_i2c_gate_mutex);
+       dbg("%s: %d (%d)", __func__, af9013_i2c_gate_ctrl_usecnt, fe->dvb->num);
+       return 0;
+}
+
 struct af9013_state {
        struct i2c_adapter *i2c;
        struct dvb_frontend fe;
@@ -44,7 +92,6 @@ struct af9013_state {
        unsigned long set_frontend_jiffies;
        unsigned long read_status_jiffies;
        bool first_tune;
-       bool i2c_gate_state;
        unsigned int statistics_step:3;
        struct delayed_work statistics_work;
 };
@@ -54,6 +101,7 @@ static int af9013_wr_regs_i2c(struct af9013_state *priv, u8 
mbox, u16 reg,
        const u8 *val, int len)
 {
        int ret;
+       struct dvb_frontend *fe = &(priv->fe);
        u8 buf[3+len];
        struct i2c_msg msg[1] = {
                {
@@ -69,6 +117,10 @@ static int af9013_wr_regs_i2c(struct af9013_state *priv, u8 
mbox, u16 reg,
        buf[2] = mbox;
        memcpy(&buf[3], val, len);
 
+       if (af9013_i2c_gate_inc_use_count(fe, GATE_NOOP) != 0) {
+               return -EAGAIN;
+       }
+       dbg("%s: I2C write reg:%04x (%d)", __func__, reg, fe->dvb->num);
        ret = i2c_transfer(priv->i2c, msg, 1);
        if (ret == 1) {
                ret = 0;
@@ -76,6 +128,10 @@ static int af9013_wr_regs_i2c(struct af9013_state *priv, u8 
mbox, u16 reg,
                warn("i2c wr failed=%d reg=%04x len=%d", ret, reg, len);
                ret = -EREMOTEIO;
        }
+
+       if (af9013_i2c_gate_dec_use_count(fe, GATE_NOOP) != 0) {
+               return -EAGAIN;
+       }
        return ret;
 }
 
@@ -84,6 +140,7 @@ static int af9013_rd_regs_i2c(struct af9013_state *priv, u8 
mbox, u16 reg,
        u8 *val, int len)
 {
        int ret;
+       struct dvb_frontend *fe = &(priv->fe);
        u8 buf[3];
        struct i2c_msg msg[2] = {
                {
@@ -103,6 +160,10 @@ static int af9013_rd_regs_i2c(struct af9013_state *priv, 
u8 mbox, u16 reg,
        buf[1] = (reg >> 0) & 0xff;
        buf[2] = mbox;
 
+       if (af9013_i2c_gate_inc_use_count(fe, GATE_NOOP) != 0) {
+               return -EAGAIN;
+       }
+       dbg("%s: I2C read reg:%04x (%d)", __func__, reg, priv->fe.dvb->num);
        ret = i2c_transfer(priv->i2c, msg, 2);
        if (ret == 2) {
                ret = 0;
@@ -110,6 +171,9 @@ static int af9013_rd_regs_i2c(struct af9013_state *priv, u8 
mbox, u16 reg,
                warn("i2c rd failed=%d reg=%04x len=%d", ret, reg, len);
                ret = -EREMOTEIO;
        }
+       if (af9013_i2c_gate_dec_use_count(fe, GATE_NOOP) != 0) {
+               return -EAGAIN;
+       }
        return ret;
 }
 
@@ -1297,25 +1361,28 @@ static int af9013_i2c_gate_ctrl(struct dvb_frontend 
*fe, int enable)
        int ret;
        struct af9013_state *state = fe->demodulator_priv;
 
-       dbg("%s: enable=%d", __func__, enable);
-
-       /* gate already open or close */
-       if (state->i2c_gate_state == enable)
-               return 0;
+       if (af9013_i2c_gate_inc_use_count(fe,
+                               enable ? GATE_ENABLE : GATE_DISABLE) != 0) {
+               return -EAGAIN;
+       }
+       dbg("%s: enable:%d (%d)", __func__, enable, fe->dvb->num);
 
        if (state->config.ts_mode == AF9013_TS_USB)
                ret = af9013_wr_reg_bits(state, 0xd417, 3, 1, enable);
        else
                ret = af9013_wr_reg_bits(state, 0xd607, 2, 1, enable);
-       if (ret)
-               goto err;
-
-       state->i2c_gate_state = enable;
+       
+       if (ret) {
+               dbg("%s: failed=%d", __func__, ret);
+       }
+       
+       if (!enable) {
+               if (af9013_i2c_gate_dec_use_count(fe, GATE_DISABLE) != 0) {
+                       return -EAGAIN;
+               }
+       }
 
        return ret;
-err:
-       dbg("%s: failed=%d", __func__, ret);
-       return ret;
 }
 
 static void af9013_release(struct dvb_frontend *fe)
-- 
1.7.5.4

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