[PATCH 3.10 45/79] [media] dib8000: make 32 bits read atomic
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: 2014-02-11 19:29:52
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3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mauro Carvalho Chehab <redacted> commit 5ac64ba12aca3bef18e61c866583155a3bbf81c4 upstream. 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 <redacted> Signed-off-by: Mauro Carvalho Chehab <redacted> Acked-by: Patrick Boettcher <redacted> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- drivers/media/dvb-frontends/dib8000.c | 33 +++++++++++++++++++++++++-------- 1 file changed, 25 insertions(+), 8 deletions(-)
--- 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 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 dib8 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 { 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])); }