Hi, I'm looking into a cpu lockup while resuming from S3. I can't paste the warning here because the serial console comes back scrambled. There are two issues: 1. The 16550A serial port is a pnp device that the pnp bus disables on suspend, despite having no_console_suspend set, and 2. ACPI suspend powers off the device anyway. I've managed to workaround these 2 issues by brute force hack, but I think that it's worthwhile to consider making no_console_suspend work properly in mainline. Not disabling the pnp device of the serial console is trivial: option 1 is to special case some return value from pnp_dev->suspend() which prevent further action by the pnp bus but does not error out of suspending, or option 2 is for the device to override pnp_dev->capabilities and turn off PNP_DISABLE. This option also requires a new capability to prevent the pnpacpi protocol from powering off the device. Option 2 is the workaround I'm using right now and it's pretty messy. The second issue is less straightforward. Since ACPI powers off the device anyway, on return from acpi_suspend_lowlevel(), the device needs some minimal re-programming. The workaround right now is to re-check a device register on every console write, and perform the re-programming if it's been cleared. This is not very robust or desirable; the power-on register value is a valid (but unlikely) state for the device. What's needed is a way to distinguish between a console write immediately before and immediately after resume, before resume starts using printk :) Ideally, consoles would get a notification before being used; optionally, a system-wide value which identifies power transition states could work. Thoughts? Regards, Peter Hurley PS - This situation is not limited to pnpacpi on x86. Several ARM designs power off the serial port, and require explicit re-programming for resume using no_console_suspend. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
