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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2014-09-10 21:29:57 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-09-26 18:01:56 +0200
commitd74d5d1b7288ff9d4439c8c7e0e314cde9743467 (patch)
treeb3fa7875cd728b9f877863a89ce478df27e74f55 /include/linux/serial_8250.h
parent234abab143aef82c0ef1f2de409c0db96b666f3c (diff)
tty: serial: 8250_core: add run time pm
While comparing the OMAP-serial and the 8250 part of this I noticed that the latter does not use run time-pm. Here are the pieces. It is basically a get before first register access and a last_busy + put after last access. This has to be enabled from userland _and_ UART_CAP_RPM is required for this. The runtime PM can usually work transparently in the background however there is one exception to this: After serial8250_tx_chars() completes there still may be unsent bytes in the FIFO (depending on CPU speed vs baud rate + flow control). Even if the TTY-buffer is empty we do not want RPM to disable the device because it won't send the remaining bytes. Instead we leave serial8250_tx_chars() with RPM enabled and wait for the FIFO empty interrupt. Once we enter serial8250_tx_chars() with an empty buffer we know that the FIFO is empty and since we are not going to send anything, we can disable the device. That xchg() is to ensure that serial8250_tx_chars() can be called multiple times and only the first invocation will actually invoke the runtime PM function. So that the last invocation of __stop_tx() will disable runtime pm. NOTE: do not enable RPM on the device unless you know what you do! If the device goes idle, it won't be woken up by incomming RX data _unless_ there is a wakeup irq configured which is usually the RX pin configure for wakeup via the reset module. The RX activity will then wake up the device from idle. However the first character is garbage and lost. The following bytes will be received once the device is up in time. On the beagle board xm (omap3) it takes approx 13ms from the first wakeup byte until the first byte that is received properly if the device was in core-off. v5…v8: - drop RPM from serial8250_set_mctrl() it will be used in restore path which already has RPM active and holds dev->power.lock v4…v5: - add a wrapper around rpm function and introduce UART_CAP_RPM to ensure RPM put is invoked after the TX FIFO is empty. v3…v4: - added runtime to the console code - removed device_may_wakeup() from serial8250_set_sleep() Cc: mika.westerberg@linux.intel.com Reviewed-by: Tony Lindgren <tony@atomide.com> Tested-by: Tony Lindgren <tony@atomide.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux/serial_8250.h')
-rw-r--r--include/linux/serial_8250.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index 6fc9d7bee05e..c267412a3ef4 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -84,6 +84,7 @@ struct uart_8250_port {
unsigned char mcr_mask; /* mask of user bits */
unsigned char mcr_force; /* mask of forced bits */
unsigned char cur_iotype; /* Running I/O type */
+ unsigned char rpm_tx_active;
/*
* Some bits in registers are cleared on a read, so they must