[U-Boot] [PATCH 1/2] dm: gpio: mxc: fix mxc_gpio_bank_get_value

[Peng Fan]

Hi Stefano,

On Sun, Apr 03, 2016 at 08:09:35PM +0200, Stefano Babic wrote:
>Hi Peng,
>
>On 17/03/2016 02:44, Peng Fan wrote:
>> On Wed, Mar 16, 2016 at 09:48:24AM -0300, Fabio Estevam wrote:
>>> Hi Peng,
>>>
>>> On Tue, Mar 15, 2016 at 10:27 PM, Peng Fan <van.freenix at gmail.com> wrote:
>>>
>>>> If set the SION bit, we need to change the pinmux settings in device tree,
>>>> however device tree are introduced from linux kernel. I would not like
>>>> to change the pinmux setting value.
>>>>
>>>> So I choose to use data register but not PSR register.
>>>
>>> Haven't checked the kernel driver, but just curious: how does the
>>> kernel handle this?
>> 
>> bgc->gc.get = bgpio_get;
>> 
>> The get method:
>> * @get: returns value for signal "offset"; for output signals this
>> *      returns either the value actually sensed, or zero
>> 
>> 138 static int bgpio_get(struct gpio_chip *gc, unsigned int gpio)
>> 139 {
>> 140         struct bgpio_chip *bgc = to_bgpio_chip(gc);
>> 141
>> 142         return !!(bgc->read_reg(bgc->reg_dat) & bgc->pin2mask(bgc, gpio));
>> 143 }
>> 
>> The gpio subsystem use reg_data. The reg_data is GPIO_PSR for gpio-mxc.c:
>> 
>> 450         err = bgpio_init(&port->bgc, &pdev->dev, 4,
>> 451                          port->base + GPIO_PSR,
>> 452                          port->base + GPIO_DR, NULL,
>> 453                          port->base + GPIO_GDIR, NULL, 0);
>> 
>> So we know that kernel gpio-mxc use GPIO_PSR for reading data, but
>> as the comments for get method "for output signals this returns
>> either the value actually sensed, or zero", if no SION bit set, reading
>> PSR will return 0 with direction output.
>> 
>
>There was already a debate in the past about this point. You can take a
>look at the commit:
>
>commit 5dafa4543c399d329c7b01df1afa98437861cac0
>Author: Benoît Thébaudeau <benoit.thebaudeau at advansee.com>
>Date:   Mon Aug 20 10:55:41 2012 +0000
>
>    mxc: Make gpio_get_value() use PSR
>
>
>There were good reasons to switch to PSR (mxc-gpio used DR before) - we
>cannot switch any time back to solve a single issue.
>
>I would like to remain compliant with Linux - your change breaks also
>boards that rely on this behavior.

Thanks for this. I'll look at whether I can have some new way.

Regards,
Peng.
>
>
>> But in U-Boot, the regulator driver needs to get the value when direction is
>> configured as output, we can use data register here or configure SION in pinmux.
>> But I prefer using data register here.
>> 
>
>Best regards,
>Stefano
>
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