Re: [RFC] What are the goals for the architecture of an in-kernel IR system?

Mauro Carvalho Chehab
2010-04-10T01:02:37Z

Jon Smirl wrote:
> On Fri, Apr 9, 2010 at 7:32 PM, Mauro Carvalho Chehab
> <mchehab@redhat.com> wrote:
>
>> [1] Yet, none of the in-hardware decoders allow resume, AFAIK. With a software
>> decoder, the IR IRQ might be used to wake, but this means that everything,
>> even a glitch, would wake the hardware, so this won't work neither.
>
> On my embedded hardware there is 100KB of static RAM on the CPU die.
> It is preserved even in deep sleep. An IR pulse can wake the CPU and
> run code in this 100KB RAM. Then the CPU can decide whether it wants
> to power on main RAM and restore the OS. But implementing this is
> outside the scope of the Linux kernel.
>
> In someways this is how an MSMCE behaves in suspend. There is code
> running on the MCU inside the MSMCE receiver. Too bad we can't tell it
> a pattern to watch for and then trigger USB wake up. It is easy to
> build a MSMCE clone, maybe someone will clone it and add the wakeup
> pattern match. An enterprising hacker can probably change the firmware
> in the existing devices.

Waking up the entire hardware just because an IRQ was triggered doesn't seem
a good idea on PC's. Here, I had to put the IR sensors behind the table
to avoid receiving too many noise from my room's lamp.
If I put it on the right place, I start receiving several of glitches per
second. I doubt this would be useful for suspend/resume operations.

--

Cheers,
Mauro