linux-kernel - Re: Re: Reset implementation for Zynq

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Message-ID: <CAKfKVtFKp8ZnLmDh-Qq5LvHTaqVafZ3P3M+E6HfvSM+Z0qYcQA@mail.gmail.com>
Date:   Tue, 8 Nov 2016 17:26:29 +0530
From:   Shubhrajyoti Datta <shubhrajyoti.datta@...il.com>
To:     iztok.jeras@...pitaya.com
Cc:     Moritz Fischer <moritz.fischer@...us.com>, p.zabel@...gutronix.de,
        linux-kernel@...r.kernel.org
Subject: Re: Re: Reset implementation for Zynq

Hi Iztok,



On Tue, Nov 8, 2016 at 3:10 PM,  <iztok.jeras@...pitaya.com> wrote:
> Hi Shubhrajyoti,
>
> By lockup state, I mean an undefined/unhandled state of the HW logic state
> machine,
> or something similar in the software driver.
> Based on symptoms I assume it is a HW lockup.
> In practice asking the driver for a new I2C transfer would result in
> nothing happening on the I2C bus (signals remain in hi-Z state).
> Driver or userspace tool reports a transfer error, but I did not copy it.
> And I did not check the state of the driver.
>
> To enter this mode it was enough to connect an oscilloscope probe to the SDA
> signal.
> The capacitance of the probe causes a deep voltage fall, which is quickly
> corrected by the pullup.
> I did not time the glitch, and the shape was partially defined by an I2C
> level shifter.
> The issue can be repeated with about 80% probability.
>
> There are two ways to get back to a working state:
> 1. create a longer zero pulse (about 50ms manual grounding) on SDA
> 2. reset the HW, this was done with a patched driver.
Thanks  for the explaination.
May be recovery mechanism  implementation could be considered.


>
> Regards,
> Iztok Jeras
>
>