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media: dvb-frontends/stv0910: release lock on gate_ctrl() failure

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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@lip6.fr>
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Daniel Scheller 2017-08-23 12:09:58 -04:00 committed by Mauro Carvalho Chehab
parent e59eb4adf0
commit 6b852620fa
1 changed files with 20 additions and 5 deletions
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25
drivers/media/dvb-frontends/stv0910.c
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@ -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;