mutex_lock in designware-i2c

mutex_lock in designware-i2c

[Rongrong Zou]

Hi, baruch

I found a mutex lock in dw_i2c_dev for each adapter,
struct dw_i2c_dev {
         struct device           *dev;
         void __iomem            *base;
         struct completion       cmd_complete;
         struct mutex            lock;
         struct clk              *clk;

but there is another lock: adapter->bus_lock, this lock is also
for each adapter, why we need both of them ?

Regards,

Rongrong

Re: mutex_lock in designware-i2c

[Baruch Siach]

Hi Rongrong Zou,

On Mon, Jan 11, 2016 at 07:12:10PM +0800, Rongrong Zou wrote:
> I found a mutex lock in dw_i2c_dev for each adapter,
> struct dw_i2c_dev {
>         struct device           *dev;
>         void __iomem            *base;
>         struct completion       cmd_complete;
>         struct mutex            lock;
>         struct clk              *clk;
> 
> but there is another lock: adapter->bus_lock, this lock is also
> for each adapter, why we need both of them ?

As far as I can see from the code the master_xfer callback is never called 
concurrently for the same adaptor. So indeed the internal lock looks 
redundant. I can't remember why I put it there.

baruch

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