23 Jan
2021
23 Jan
'21
7:09 p.m.
Hi Andy,
On Thu, 29 Oct 2020 at 06:22, Andy Shevchenko andriy.shevchenko@linux.intel.com wrote:
On Tue, Sep 22, 2020 at 12:45:43PM -0600, Simon Glass wrote:
Add some documentation provided by Andy Shevchenko to describe how to use struct acpi_gpio.
Thanks!
I see Bin already applied this, perhaps follow up fix is needed. See below.
...
- Note that GpioIo doesn't have any means of Active Low / High setting, so a
GpioIo -> GpioIo()
- _DSD must be provided to mitigate this.
Plus the following:
"This parameter does not make sense for GpioInt() since it has its own means to define it."
- GpioIo doesn't properly communicate the initial state of the output pin,
GpioIo -> GpioIo()
- thus Linux assumes the simple rule:
- Pull Bias Polarity Requested...
- Implicit x AS IS (assumed firmware configured for us)
- Explicit x (no _DSD) as Pull Bias (Up == High, Down == Low),
assuming non-active (Polarity = !Pull Bias)
- Down Low as low, assuming active
- Down High as high, assuming non-active
Should be read:
" * Down High as low, assuming non-active"
- Up Low as high, assuming non-active
- Up High as high, assuming active
- GpioIo() can be used as interrupt and in this case the IoRestriction mustn't
- be OutputOnly.
- It also requires active_low flag from _DSD in cases where it's
- needed (better to always provide than rely on above assumption made on OS
- level).
Thanks, I sent a patch for these.
Regards, Simon