From: Daniel Scheller <d.scheller@xxxxxxx>
Whenever write_reg() fails to open/close the demod's I2C gate, release the
lock to avoid deadlocking situations. If I2c gate open failed, there's no
need to hold a lock, and if close fails, the mutex_unlock() at the end of
the function is never reached, leaving the mutex_lock in locked state,
which in turn will cause potential for deadlocks. Thus, release the lock
on failure.
While we're touching gate_ctrl(), add some explanation about the need for
locking and the shared I2C bus/gate.
Cc: Julia Lawall <julia.lawall@xxxxxxx>
Signed-off-by: Daniel Scheller <d.scheller@xxxxxxx>
---
drivers/media/dvb-frontends/stv0910.c | 25 ++++++++++++++++++++-----
1 file changed, 20 insertions(+), 5 deletions(-)
diff --git a/drivers/media/dvb-frontends/stv0910.c b/drivers/media/dvb-frontends/stv0910.c
index d1ae9553f74c..0d4a6a115159 100644
--- a/drivers/media/dvb-frontends/stv0910.c
+++ b/drivers/media/dvb-frontends/stv0910.c
@@ -1221,17 +1221,32 @@ static int gate_ctrl(struct dvb_frontend *fe, int enable)
struct stv *state = fe->demodulator_priv;
u8 i2crpt = state->i2crpt & ~0x86;
- if (enable)
- mutex_lock(&state->base->i2c_lock);
+ /*
+ * mutex_lock note: Concurrent I2C gate bus accesses must be
+ * prevented (STV0910 = dual demod on a single IC with a single I2C
+ * gate/bus, and two tuners attached), similar to most (if not all)
+ * other I2C host interfaces/busses.
+ *
+ * enable=1 (open I2C gate) will grab the lock
+ * enable=0 (close I2C gate) releases the lock
+ */
- if (enable)
+ if (enable) {
+ mutex_lock(&state->base->i2c_lock);
i2crpt |= 0x80;
- else
+ } else {
i2crpt |= 0x02;
+ }
if (write_reg(state, state->nr ? RSTV0910_P2_I2CRPT :
- RSTV0910_P1_I2CRPT, i2crpt) < 0)
+ RSTV0910_P1_I2CRPT, i2crpt) < 0) {
+ /* don't hold the I2C bus lock on failure */
+ mutex_unlock(&state->base->i2c_lock);
+ dev_err(&state->base->i2c->dev,
+ "%s() write_reg failure (enable=%d)\n",
+ __func__, enable);
return -EIO;
+ }
state->i2crpt = i2crpt;
--
2.13.0
