linux-kernel - Re: [PATCH v2 2/3] i2c: pxa: prevent calling of the generic recovery init code

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Message-ID: <1261d3ed-e057-45b1-913e-f8bf1cd5d7bc@gmail.com>
Date: Sun, 17 Aug 2025 16:59:22 +0200
From: Gabor Juhos <j4g8y7@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Wolfram Sang <wsa@...nel.org>,
 Wolfram Sang <wsa+renesas@...g-engineering.com>,
 Andi Shyti <andi.shyti@...nel.org>, Andrew Lunn <andrew@...n.ch>,
 Hanna Hawa <hhhawa@...zon.com>, Robert Marko <robert.marko@...tura.hr>,
 Linus Walleij <linus.walleij@...aro.org>, linux-i2c@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Imre Kaloz <kaloz@...nwrt.org>, stable@...r.kernel.org
Subject: Re: [PATCH v2 2/3] i2c: pxa: prevent calling of the generic recovery
 init code

2025. 08. 13. 17:28 keltezéssel, Russell King (Oracle) írta:
> On Wed, Aug 13, 2025 at 05:17:28PM +0200, Gabor Juhos wrote:
>> 2025. 08. 13. 15:10 keltezéssel, Andy Shevchenko írta:
>>> On Wed, Aug 13, 2025 at 12:36:45PM +0200, Gabor Juhos wrote:
>>>> 2025. 08. 11. 22:26 keltezéssel, Andy Shevchenko írta:
>>>>> On Mon, Aug 11, 2025 at 09:49:56PM +0200, Gabor Juhos wrote:
>>>
>>> ...
>>>
>>>>> TBH this sounds to me like trying to hack the solution and as you pointed out
>>>>> the problem is in pinctrl state changes. I think it may affect not only I2C case.
>>>>
>>>> It is not an error in the pinctrl code. I have checked and even fixed a few bugs
>>>> in that.
>>>>
>>>>> And I didn't get how recovery code affects the initialisation (enumeration).
>>>>
>>>> Without the fix, it is not possible to initiate a transaction on the bus, which
>>>> in turn prevents enumeration.
>>>
>>> But why? As you said below the first pin control state is changed during the
>>> probe, which is fine, and the culprit one happens on the recovery.
>>
>> Erm, no. Both happens during probe, before the I2C core tries to enumerate the
>> devices on the bus.
>>
>>> Why is recovery involved in probe? This is quite confusing...
>> Let me try to explain it differently. Here is the simplified call chain:
>>
>>   i2c_pxa_probe()
>>      ...
>>      i2c_pxa_init_recovery()
>>         pinctrl_select_state()                  <- selects GPIO state
>>         pinctrl_select_state()                  <- selects default (I2C) state
>>      ...
>>      i2c_add_numbered_adapter()
>>          i2c_register_adapter()
>>              ...
>>              i2c_init_recovery()
>>                  i2c_gpio_init_recovery()
>>                      i2c_gpio_init_generic_recovery()
>>                          pinctrl_select_state() <- selects GPIO state***
>>                          ...
>>                          pinctrl_select_state() <- selects default (I2C) state
>>              ...
>>              bus_for_each_drv()
>>                  __process_new_adapter()
>>                      i2c_do_add_adapter()
>>                          i2c_detect()           <- enumerates the devices
>>
>> The culprit is the first pinctrl_select_state() call in
>> i2c_gpio_init_generic_recovery() marked with '***'.
>>
>> That call causes the controller to go stuck, which makes it impossible to
>> transfer anything on the bus.
> 
> Probably because when GPIO state is selected, the I2C bus pins end up
> being set low, which the I2C controller sees, so it thinks there's
> another device communicating on the bus.

Yes, it seems so.

When GPIO state is selected, the bits in the Bus Monitor register which are
continuously reflecting the value of the SCL and SDA pins contains zeros.

Additionally, the Status register indicates an 'Early Bus Busy' condition, which
means that 'The SCL or SDA line is low, without a Start condition'.


> I could be wrong, as I don't have the hardware to hand to research
> the issue again.
> 
> I have a vague memory that the GPIO state must _always_ reflect the
> actual pin state before switching to it to avoid glitches and avoid
> inadvertently changing the I2C controller state.

Unfortunately, it only helps to avoid glitches on the external lines. At least,
in the current case the controller hungs no matter which value combination is
being set on the GPIO pins before switching to GPIO state.


Regards,
Gabor