Re: resume path in dra7xx and other DW-based drivers

[Kishon Vijay Abraham I <kishon@ti.com>]

Hi Bjorn,

On Friday 09 December 2016 02:13 AM, Bjorn Helgaas wrote:
> On Thu, Dec 08, 2016 at 02:19:00PM +0530, Kishon Vijay Abraham I wrote:
>> Hi Bjorn,
>>
>> On Thursday 08 December 2016 03:32 AM, Bjorn Helgaas wrote:
>>> Hi Kishon, et al,
>>>
>>> Does dra7xx suspend/resume work?  I'm not sure dra7xx_pcie_resume()
>>> and dra7xx_pcie_resume_noirq() restore everything necessary.  For
>>> example, the probe path has this:
>>>
>>>   dra7xx_pcie_probe
>>>     dra7xx_add_pcie_port
>>>       dw_pcie_host_init
>>> 	dra7xx_pcie_host_init         # .host_init
>>> 	  dw_pcie_setup_rc
>>> 	    dw_pcie_prog_outbound_atu
>>>
>>> so I think it programs the ATU in dw_pcie_setup_rc().  But the resume
>>> path doesn't call dw_pcie_setup_rc(), so I don't see where the ATU
>>> setup would be restored.
>>
>> DRA7xx only supported shallow power state and not deep power state. In shallow
>> power state, the register settings are not lost and hence we didn't have to
>> restore anything.
> 
> I'm not really a PM guy, so I'm not familiar with shallow power state.
> Could I have discovered from the code somehow that dra7xx suspend to
> shallow power state preserves register state?  It's nice if a reader
> can verify correctness without knowing the system-specific details.

Some drivers like drivers/mmc/host/omap_hsmmc.c saves the register contents
(omap_hsmmc_context_save) and then in runtime_resume checks if the register
contents are still same (omap_hsmmc_context_restore). Do you think we have to
do something like that for dra7xx?

omap_hsmmc.c is used by a lot of platforms some of which loses the context
during suspend. Since dra7xx doesn't loose context, not sure if we have to do
something like omap_hsmmc.

Thanks
Kishon