Re: [PATCH] - race-free suspend. Was: Re: [PATCH 0/8] Suspend block api (version 8)

On Wed, Jun 02, 2010 at 07:44:59PM -0700, Arve Hjønnevåg wrote:

On Wed, Jun 2, 2010 at 4:32 PM, Dmitry Torokhov
[off-list ref] wrote:

quoted

On Wed, Jun 02, 2010 at 09:05:21PM +0200, Florian Mickler wrote:

quoted

On Wed, 2 Jun 2010 21:02:24 +1000
Neil Brown [off-list ref] wrote:

quoted

And this decision (to block suspend) really needs to be made in the driver,
not in userspace?

Well, it fits. The requirement is a direct consequence of the intimate
knowledge the driver has about the driven devices.

That is not really true. A driver does have intimate knowledge of the
device, however it does not necessarily have an idea about the data read
from the device. Consider the gpio_matrix driver: Arve says that it has
to continue scanning matrix once first interrupt arrvies. But it really
depends on what key has been pressed - if user pressed KEY_SUSPEND or
KEY_POWER it cmight be better if we did not wait for key release but
initiated the action right away. The decision on how system reacts to a
key press does not belong to the driver but really to userspace.

If we just suspend while the keypad scan is active, a second press of
KEY_POWER would not be able wake the device up. The gpio keypad matrix
driver has two operating modes. No keys are pressed: all the outputs
are active so a key press will generate an interrupt in one of the
inputs. Keys are pressed: Activate a single output at a time so we can
determine which keys are pressed. The second mode is entered when the
driver gets an interrupt in the first mode. The first mode is entered
if the scan detected that no keys are pressed. The driver could be
modified to stop the scan on suspend and forcibly put the device back
in no-keys-pressed state, but pressing additional keys connected to
the same input can no longer generate any events (the input does not
change).

Would that be still the case if you reprogram the device as wakeup
source while suspending?

Anyway, it does not really matter. Your case (current suspend blockers)
would delay putting device to sleep till you release all the keys,
including KEY_POWER. If you delegate the decision to userspace it would
have an _option_ of putting the device to sleep earlier, however in both
cases user has to release all keys before the device can be resumed.

-- 
Dmitry