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| author | Peter Hurley <peter@hurleysoftware.com> | 2015-01-22 12:24:30 -0500 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-02-02 10:11:27 -0800 |
| commit | 4516d50aabedbe5ae334155193e4d35c02390d9a (patch) | |
| tree | 19bcf6aba42e65701008dce683481dce7008fef9 /include/linux/serial_8250.h | |
| parent | 06a4c710673184f5c750bdb2f8579e0ae1cc252c (diff) | |
| download | linux-4516d50aabedbe5ae334155193e4d35c02390d9a.tar.gz linux-4516d50aabedbe5ae334155193e4d35c02390d9a.tar.bz2 linux-4516d50aabedbe5ae334155193e4d35c02390d9a.zip | |
serial: 8250: Use canary to restart console after suspend
When using no_console_suspend, the serial console may be powered off
anyway during system sleep. Upon resume, the port may be in its default
power-on state, but is expected to continue console i/o before the device
has received its pm callback. The resultant garbage i/o can cause all
kinds of havoc on the remote end.
Use the scratch register as a canary to discover if the console
has been powered-off. Write a non-zero value to the scratch register
at port suspend and reprogram the port before any console i/o if the
scratch register != canary before port resume.
This workaround is disabled for omap_8250 (which uses different divisor
programming).
Credit to Doug Anderson <dianders@chromium.org> for the idea of using
the scratch register canary to discover port power-down.
Cc: Doug Anderson <dianders@chromium.org>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux/serial_8250.h')
| -rw-r--r-- | include/linux/serial_8250.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index 245b959f1ff6..a8efa235b7c1 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -85,6 +85,9 @@ struct uart_8250_port { unsigned char mcr_force; /* mask of forced bits */ unsigned char cur_iotype; /* Running I/O type */ unsigned int rpm_tx_active; + unsigned char canary; /* non-zero during system sleep + * if no_console_suspend + */ /* * Some bits in registers are cleared on a read, so they must |