Re: [PATCH v2 4/6] ARM: at91/dt: sama5d3: add i2c gpio pinctrl

Codrin.Ciubotariu
2020-01-06T16:58:49Z

On 05.01.2020 00:39, Peter Rosin wrote:
> On 2020-01-03 10:49, Codrin.Ciubotariu@microchip.com wrote:
>> From: Kamel Bouhara <kamel.bouhara@bootlin.com>
>>
>> Add the i2c gpio pinctrls to support the i2c bus recovery
>>
>> Signed-off-by: Kamel Bouhara <kamel.bouhara@bootlin.com>
>> ---
>>
>> Changes in v2:
>> - none;
>>
>> arch/arm/boot/dts/sama5d3.dtsi | 33 ++++++++++++++++++++++++++++++---
>> 1 file changed, 30 insertions(+), 3 deletions(-)
>>
>
> *snip*
>
>> @@ -639,6 +648,12 @@
>> <AT91_PIOA 30 AT91_PERIPH_A AT91_PINCTRL_NONE /* PA30 periph A TWD0 pin, conflicts with URXD1, ISI_VSYNC */
>> AT91_PIOA 31 AT91_PERIPH_A AT91_PINCTRL_NONE>; /* PA31 periph A TWCK0 pin, conflicts with UTXD1, ISI_HSYNC */
>> };
>> +
>> + pinctrl_i2c0_gpio: i2c0-gpio {
>> + atmel,pins =
>> + <AT91_PIOA 30 AT91_PERIPH_GPIO AT91_PINCTRL_PULL_UP
>> + AT91_PIOA 31 AT91_PERIPH_GPIO AT91_PINCTRL_PULL_UP>;
>> + };
>
> I'm curious, but why are pull-ups suddenly needed just because the pins are
> used for GPIO recovery? Why are pull-ups not needed when the pins are used
> by the I2C peripheral device(s)?
>
> Given figure 27-2 "I/O Line Control Logic" in my SAMA5D3 datasheet, I see
> no difference as to how and why the pull-ups are applied depending on what
> the current function of the pin is. So, if the I2C bus works w/o pulls, bus
> recovery using GPIO must also work w/o pulls.
>
> I.e. the device tree requires you to have external pull-ups on the I2C bus
> anyway, so why bother with internal pull-ups for the recovery case?
>
> Changing pull-up settings just for recovery feels like something that will
> inevitably create hard to debug surprises at the least opportune time...
>
> Or am I missing something?
>
> (I'm focusing on SAMA5D3 since that is what I happen to work with,
> but the same question appears to apply for SAMA5D2 and SAMA5D4...)

I don't think we need the pull-ups. I will remove them in v3.

Thanks and best regards,
Codrin