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@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 zero138 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@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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