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

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Message-ID: <c765455f-c1b9-2da0-675e-591f7c268d99@kernel.org>
Date:   Tue, 12 Jul 2022 07:41:06 -0500
From:   Dinh Nguyen <dinguyen@...nel.org>
To:     Wolfram Sang <wsa@...nel.org>, jarkko.nikula@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com, mika.westerberg@...ux.intel.com,
        robh+dt@...nel.org, krzk+dt@...nel.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCHv6 1/2] i2c: designware: introduce a custom scl recovery
 for SoCFPGA platforms

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.

Dinh