[PATCH 3.5 24/88] [media] dib8000: make 32 bits read atomic

From: Luis Henriques
Date: Fri Feb 07 2014 - 08:33:04 EST


3.5.7.30 -stable review patch. If anyone has any objections, please let me know.

------------------

From: Mauro Carvalho Chehab <m.chehab@xxxxxxxxxxx>

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 <m.chehab@xxxxxxxxxxx>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@xxxxxxxxxxx>
Acked-by: Patrick Boettcher <pboettcher@xxxxxxxxxxxxxx>
[ luis: backported to 3.5:
- file rename: drivers/media/dvb-frontends/dib8000.c ->
drivers/media/dvb/frontends/dib8000.c ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
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 9ca34f4..0b8c1bb 100644
--- a/drivers/media/dvb/frontends/dib8000.c
+++ b/drivers/media/dvb/frontends/dib8000.c
@@ -118,15 +118,10 @@ 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;

@@ -144,6 +139,21 @@ 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;
@@ -153,8 +163,15 @@ 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]));
}
--
1.8.3.2

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