From 5ac64ba12aca3bef18e61c866583155a3bbf81c4 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Fri, 13 Dec 2013 10:35:03 -0300 Subject: [PATCH] [media] dib8000: make 32 bits read atomic As the dvb-frontend kthread can be called anytime, it can race with some get status ioctl. So, it seems better to avoid one to race with the other while reading a 32 bits register. I can't see any other reason for having a mutex there at I2C, except to provide such kind of protection, as the I2C core already has a mutex to protect I2C transfers. Note: instead of this approach, it could eventually remove the dib8000 specific mutex for it, and either group the 4 ops into one xfer or to manually control the I2C mutex. The main advantage of the current approach is that the changes are smaller and more puntual. Signed-off-by: Mauro Carvalho Chehab Cc: stable@vger.kernel.org Signed-off-by: Mauro Carvalho Chehab Acked-by: Patrick Boettcher --- drivers/media/dvb-frontends/dib8000.c | 33 ++++++++++++++++++++------- 1 file changed, 25 insertions(+), 8 deletions(-) diff --git a/drivers/media/dvb-frontends/dib8000.c b/drivers/media/dvb-frontends/dib8000.c index 1e03961135ac..36c839cabe82 100644 --- a/drivers/media/dvb-frontends/dib8000.c +++ b/drivers/media/dvb-frontends/dib8000.c @@ -157,15 +157,10 @@ static u16 dib8000_i2c_read16(struct i2c_device *i2c, u16 reg) return ret; } -static u16 dib8000_read_word(struct dib8000_state *state, u16 reg) +static u16 __dib8000_read_word(struct dib8000_state *state, u16 reg) { u16 ret; - if (mutex_lock_interruptible(&state->i2c_buffer_lock) < 0) { - dprintk("could not acquire lock"); - return 0; - } - state->i2c_write_buffer[0] = reg >> 8; state->i2c_write_buffer[1] = reg & 0xff; @@ -183,6 +178,21 @@ static u16 dib8000_read_word(struct dib8000_state *state, u16 reg) dprintk("i2c read error on %d", reg); ret = (state->i2c_read_buffer[0] << 8) | state->i2c_read_buffer[1]; + + return ret; +} + +static u16 dib8000_read_word(struct dib8000_state *state, u16 reg) +{ + u16 ret; + + if (mutex_lock_interruptible(&state->i2c_buffer_lock) < 0) { + dprintk("could not acquire lock"); + return 0; + } + + ret = __dib8000_read_word(state, reg); + mutex_unlock(&state->i2c_buffer_lock); return ret; @@ -192,8 +202,15 @@ static u32 dib8000_read32(struct dib8000_state *state, u16 reg) { u16 rw[2]; - rw[0] = dib8000_read_word(state, reg + 0); - rw[1] = dib8000_read_word(state, reg + 1); + if (mutex_lock_interruptible(&state->i2c_buffer_lock) < 0) { + dprintk("could not acquire lock"); + return 0; + } + + rw[0] = __dib8000_read_word(state, reg + 0); + rw[1] = __dib8000_read_word(state, reg + 1); + + mutex_unlock(&state->i2c_buffer_lock); return ((rw[0] << 16) | (rw[1])); } -- GitLab