[RFC] ARM: OMAP2+: omap_device: add pinctrl handling

Hi Grygorii,

Grygorii Strashko [off-list ref] writes:

Before switching to DT pinctrl states of OMAP IPs have been handled by hwmod
framework. After switching to DT-boot the pinctrl handling was dropped from
hwmod framework and, as it was recommended, OMAP IP's drivers have to be updated
to handle pinctrl states by itself using pinctrl_pm_select_xx() helpers
(see http://lists.infradead.org/pipermail/linux-arm-kernel/2013-June/173514.html)

But this is not right for OMAP2+ SoC where real IPs state is controlled
by omap_device core which enables/disables modules & clocks actually.

For example, if OMAP I2C driver will handle pinctrl state during system wide
suspend the following issue may occure:
- suspend_noirq - I2C device can be still active because of PM auto-suspend
  |-_od_suspend_noirq
     |- omap_i2c_suspend_noirq
        |- PINs state set to SLEEP
  |- pm_generic_runtime_suspend
     |- omap_i2c_runtime_suspend()
        |- PINs state set to IDLE  <--- *oops* PINs state is IDLE and not SLEEP
  |- omap_device_idle()
     |- omap_hwmod_idle()
        |- _idle()
           |- disbale module (sysc&clocks)

- resume_noirq - I2C was active before suspend
  |-_od_resume_noirq
     |- omap_hwmod_enable()
        |- _enable()
           |- enable module (sysc&clocks)
     |- pm_generic_runtime_resume
        |- omap_i2c_runtime_resume()
           |- PINs state set to DEFAULT  <--- !!!!
     |- omap_i2c_resume_noirq
        |- PINs state set to DEFAULT
        |- PINs state set to IDLE  <--- *big oops* we have active module and its
                                         PINs state is IDLE
(see https://patchwork.kernel.org/patch/2642101/)

Of course, everything can be handled by adding a tons of code in ecah driver to
check PM state of device and override default behavior of omap_device core, but
this not good.

Hence, add pinctrl handling in omap_device core:
1) on PM runtime resume
- switch pinctrl state to "default" (todo: "active")
2) on PM runtime suspend
- switch pinctrl state to "idle"
3) during system wide suspend
- switch pinctrl state to "sleep" or "idle" if omap_device core disables device
- switch pinctrl state to "sleep" if device is disabled already
4) during system wide resume
- switch pinctrl state to "default" (todo: "active") if omap_device core has
  disabled  device during suspend
- switch pinctrl state to "idle" if device was already disabled before suspend

This will enable pinctrl for all OMAP2+ IP's drivers by default -
no changes in code is needed and only DT data will need to be updated
(add "default", "active", "idle", "sleep" states).

This will enable pinctrl handling for all OMAP2+ drivers by default -
no changes in code is needed and only DT data will need to be updated
(add "default", "active", "idle", "sleep" states).

Related discussions:
- [3/3] i2c: nomadik: use pinctrl PM helpers 
 https://patchwork.kernel.org/patch/2670291/
- mmc: omap_hsmmc: Remux pins to support SDIO interrupt and PM runtime
 https://patchwork.kernel.org/patch/2690191/
- [PATCH 00/11] drivers: Add Pinctrl PM support
 https://lkml.org/lkml/2013/5/31/210

CC: Hebbar Gururaja <redacted>
CC: Linus Walleij  <redacted>
CC: linux-arm-kernel at lists.infradead.org
CC: linux-omap at vger.kernel.org
CC: linux-kernel at vger.kernel.org 

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
---
Hi Kevin, Tony,

I've verified this patch on OMAP4 SDP board:
- PM runtime for I2C4, UART2, UART3
- suspend/resume with I2C4, UART2, UART3

seems it works and pinctrl states have been updated as expected.

Thanks for working on this.

I agree with the approach, and much prefer this to boiler plate code
throughout the drivers.

I suggest we wait until the dust settles on the active/default thread
before taking this further, but have no objections to the approach.

Kevin