On Mon, 13 Aug 2007, Scott Wood wrote:
> On Mon, Aug 13, 2007 at 12:27:30AM +0200, Guennadi Liakhovetski wrote:
> > A number of Linkstation models from Buffalo Technology with PPC, ARM, and
> > also MIPS (I think) CPUs have a power-management controller connected to a
> > UART. Among other things that chip controlls power and reset buttons.
> > Working on a standby support for one of these systems (ppc mpc8241 based),
> > the only suitable wakeup source there is the power button, which means, I
> > have to configure one of the two system UARTs to not be suspendsd. Using
> > the device_*_wakeup API doesn't quite work because both serial ports share
> > one device. The below patch proposes a new port flag UPF_MAY_WAKEUP to
> > configure such UARTs. It also adds support for a new "can-wakeup" serial
> > node property to the legacy_serial driver.
>
> Shouldn't the ability to wakeup be configured through sysfs, rather than
> encoded into the device tree? I'm assuming this is just a matter of
> configuration, and not that the hardware supports waking from one and not
> the other.
Well, sort of. One of them is more "natural" - it has a button on the
front panel, to use the other one you have to modify the hardware.
However, I like the idea - generally it does seem to be a better approach
to have it run-time configurable over sysfs... Only - how? The only
differentitaion ATM between the two ports are these two links:
# ls -l /sys/devices/platform/serial8250.0/tty*
lrwxrwxrwx 1 root root 0 Aug 13 22:05 /sys/devices/platform/serial8250.0/tty:ttyS0 -> ../../../class/tty/ttyS0
lrwxrwxrwx 1 root root 0 Aug 13 22:05 /sys/devices/platform/serial8250.0/tty:ttyS1 -> ../../../class/tty/ttyS1
And placing some wakeup file under the class/tty/ directory doesn't seem
very consistent with the current policy - until now they only live under
devices/... (Greg added to cc:).
Actually, it is good you replied, Scott:-) I wanted to ask you about the
following: I've switched to your generic suspend/resume routines using the
_TLF_NAPPING bit, the arch_suspend_{dis,en}able_irqs() hooks... On wakeup
your _TLF_NAPPING trick should bypass calling the ISR and jump directly to
the resume code. However, on wakeup, it looks like I do get the wakeup
interrupt too. Is it the correct behaviour and is this the (approximately)
correct explanation why:
1. the AVR connected to ttyS0 sends 1 byte on button press and 1 byte on
button release. So, normally you would get 2 bytes and 2 interupts for one
such button down-up.
2. Interrupt is configured as edge (is it correct - haven't found in
mpc8245um, UARTs are usually edge), so,
--- button down -> byte #1 -> IRQ line active -> IC interrupts
--- on resume interrupts are disabled, an EOI is performed (the line is
still active)
--- interrupts are re-enabled
3. a second interrupt for the same byte is delivered.
I'm just trying to understand whether this is the correct and expected
behaviour or something is wrong here.
Thanks
Guennadi
---
Guennadi Liakhovetski
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