lkml.org 
[lkml]   [2012]   [Feb]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH V1 2/3] Documentation: gpio: Add details of open-drain configuration
On Tuesday 14 February 2012 03:36 AM, Mark Brown wrote:
> * PGP Signed by an unknown key
>
>> Implicitly, the gpio api already supports open-drain and several drivers
>> make use of it. Instead of being a separate flag; users who need open
>> drain will set the pin to input. For example, see the i2c-gpio driver.
>> I'm not convinced this is needed; but my opinion could be swayed.
> The actual idea is to provide support for doing the switch to input to
> drivers that just want to set a logic level and don't (at their level)
> care one way or another if it's a CMOS or open drain output but instead
> leaves it up to board configuration which mode is used. Laxman posted a
> patch for doing this to a regulator driver but looking at it the code
> for emulating open drain while also maintaining support for regular CMOS
> is fiddly enough that it seemed like it should be factored out of the
> individual drivers.
>

Implementing open-drain handling in every gpio client (like
i2c-gpio/regulator/fixed.c) is just duplicating the code everywhere.
Also it leaves to have such implementation buggy which is in following
piece of code (taken from i2c-gpio.c)

if (pdata->sda_is_open_drain) {
gpio_direction_output(pdata->sda_pin, 1);
bit_data->setsda = i2c_gpio_setsda_val;
} else {
gpio_direction_input(pdata->sda_pin);
bit_data->setsda = i2c_gpio_setsda_dir;
}

Header says
* @sda_is_open_drain: SDA is configured as open drain, i.e. the pin
* isn't actively driven high when setting the output value high.
* gpio_get_value() must return the actual pin state even if the
* pin is configured as an output.

And hence the check should be
if (!pdata->sda_is_open_drain) {
:::::
}


All these can be avoided by supporting open-drain flag and handling in
gpio library.

>> Also, you should include a patch to make i2c-gpio.c use this new
>> functionality as a proof-of-concept. You may not be able to test it,
>> but it will make it a lot easier to justify merging by showing how it
>> cleans up a gpio user.

I can do the cleanup in i2c-gpio also which will reduce lots of code if
this change in gpiolib is acceptable and fine with everyone.
Let me know if patch regulator/fixed.c V1 is sufficient or not to
justify. I will create the patch for i2c-gpio also.




\
 
 \ /
  Last update: 2012-02-14 10:03    [W:0.085 / U:0.588 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site