Re: linux-next regression caused by "gpiolib: request the gpio before querying its direction"

[Gregory CLEMENT <gregory.clement@xxxxxxxxxxxxxxxxxx>]

Hi Timur,
 
 On mer., août 30 2017, Timur Tabi <timur@xxxxxxxxxxxxxx> wrote:

> On 8/30/17 4:24 AM, Thomas Petazzoni wrote:
>> Therefore, with Timur's commit applied, when the system boots, we get
>> serial output, up to the point where gpiochip_add_data() is called, and
>> requests all GPIOs. Since our UART pins are not requested at the
>> pinctrl level, the gpio_request succeeds and re-muxes those pins as
>> GPIOs: we lose the UART.
>
> This part I don't understand.  My patch just only impacts the code
> that queries the direction of the GPIO.  It does not set the
> direction.
>
> When gpiochip_add_data() calls chip->request, what function is that
> calling?

the request callback is gpiochip_generic_request so I would be surprised
that there was a bug in it.

>
> The only thing I can think of is that the ->request function is not
> just returning status, but is also muxing the GPIO.  If so, then I
> think that's a bug.

Gregory

>
> -- 
> Sent by an employee of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the
> Code Aurora Forum, hosted by The Linux Foundation.
>

-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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