Re: [PATCHv6 1/2] i2c: designware: introduce a custom scl recovery for SoCFPGA platforms

[Dinh Nguyen]

On 7/12/22 07:41, Dinh Nguyen wrote:
> Hi Wolfram,
>
> On 6/22/22 15:07, Wolfram Sang wrote:
> > >  From the original code, the first mechanism to a recovery is to 
> > > acquire a
> > > GPIO for the SCL line and send the 9 SCL pulses, after that, it does 
> > > a reset
> > > of the I2C module. For the SOCFPGA part, there is no GPIO line for 
> > > the SCL,
> > > thus the I2C module cannot even get a reset. This code allows the 
> > > function
> > > to reset the I2C module for SOCFPGA, which is the 2nd part of the 
> > > recovery
> > > process.
> >
> > The second part is totally useless if the client device is holding SDA
> > low. Which is exactly the situation that recovery tries to fix. As I
> > said, if you can't control SCL, you don't have recovery.
>
> This is recovery of the master and not the slave.  We have a customer 
> that is the using I2C with the signals routed through the FPGA, and thus 
> are not GPIO. During a timeout, with this code, the driver is able to 
> recover the master.

Adding a bit more, because of patch:

ca382f5b38f3 ("i2c: designware: add i2c gpio recovery option")

the driver is now not able to reset the controller at all because it has 
placed a strict dependency on getting a GPIO. Before this patch, during 
a timeout, there was a simple call to i2c_dw_init_master(), which 
ultimately resets the master.

Dinh