Re: [PATCH 3/3] [media] az6007: handle CI during suspend/resume

[Antti Palosaari <crope@iki.fi>]

On 08/07/2012 02:41 PM, Mauro Carvalho Chehab wrote:
> Em 06-08-2012 09:21, Antti Palosaari escreveu:
>> On 08/05/2012 08:44 PM, Mauro Carvalho Chehab wrote:
>>> The dvb-usb-v2 core doesn't know anything about CI. So, the
>>> driver needs to handle it by hand. This patch stops CI just
>>> before stopping URB's/RC, and restarts it before URB/RC start.
>>>
>>> It should be noticed that suspend/resume is not yet working properly,
>>> as the PM model requires the implementation of reset_resume:
>>>      dvb_usb_az6007 1-6:1.0: no reset_resume for driver dvb_usb_az6007?
>>> But this is not implemented there at dvb-usb-v2 yet.
>>
>> That is true, but it is coming:
>> http://blog.palosaari.fi/2012/07/dvb-power-management-on-suspend.html
>> http://git.linuxtv.org/anttip/media_tree.git/shortlog/refs/heads/dvb_core3
>>
>> At the time I added initial suspend/resume support for dvb-usb-v2 I left those out purposely as I saw some study and changes are needed for DVB-core/frontend.
>>
>> Normally suspend keeps USB-device powered and calls .resume() on resume. But on certain conditions USB device could lose power
>> during suspend and on that case reset_resume() is called, and if there is no reset_resume() is calls disconnect() (and probe() after that).
>
> This should depend on BIOS settings, and what of the following type of suspend[1]
> was done:
> 	S1: All processor caches are flushed, and the CPU(s) stops executing instructions.
> 	    Power to the CPU(s) and RAM is maintained; devices that do not indicate they
> 	    must remain on may be powered down.
> 	S2: CPU powered off. Dirty cache is flushed to RAM.
> 	S3: Commonly referred to as Standby, Sleep, or Suspend to RAM. RAM remains powered
> 	S4: Hibernation or Suspend to Disk. All content of main memory is saved to non-volatile
> 	    memory such as a hard drive, and is powered down.
>
> [1] http://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface

That was something I was already aware. There is even S5 and S4b 
mentioned by Kernel documentation. But in real life you have to care only:
S3, Suspend, suspend to ram
S4, Hibernation, suspend to disk

And from the USB-driver point of view those are covered by there three 
callbacks:
.suspend()
.resume()
.reset_resume()
* if reset_resume() does not exits .disconnect() + .probe() is called 
instead

What is my current understanding S3 level leaves USB/PCI powered 
normally, but device driver should drop device to low power state. In 
case of DVB -device this means all sub-drivers should put sleep.

S4 naturally powers everything off. Also worth to mention laptops will 
switch from S3 to S4 if battery drains empty during S3.

> There are also some per-device sysfs nodes that control how PM will work for them.
> See:
>
>   $ tree /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-8/dvb/dvb0.frontend0
> /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-8/dvb/dvb0.frontend0
> ├── dev
> ├── device -> ../../../1-8
> ├── power
> │   ├── async
> │   ├── autosuspend_delay_ms
> │   ├── control
> │   ├── runtime_active_kids
> │   ├── runtime_active_time
> │   ├── runtime_enabled
> │   ├── runtime_status
> │   ├── runtime_suspended_time
> │   └── runtime_usage
> ├── subsystem -> ../../../../../../../class/dvb
> └── uevent
>
> There are a number of pm functions that can change the power management behavior
> as well.
>
> Not sure how to control it, but, IMHO, for a media device, it only makes sense
> to keep it powered on suspend if the device has IR and if the power button of
> the IR could be used to wake up the hardware. Otherwise, the better is to just
> power it off, to save battery (for notebooks).

yeah, and it was already done.

> Maybe it makes sense to talk with Raphael Wysocki to be sure that it will cover
> all possible cases: auto-suspend, S1/S2/S3/S4 and "wake on IR").

That IR was something I wasn't noticed at all. Currently it stops IR 
polling too. If that kind of functionality is needed it is surely some 
more work as you cannot stop IR-polling. Maybe I will skip it that time 
as I don't have time for it currently :) If someone wish to learn how 
USB polling remote could be used for wake-up computer then feel free to 
do that.

regards
Antti

-- 
http://palosaari.fi/