[PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx
From: bigeasy@linutronix.de (Sebastian Andrzej Siewior)
Date: 2014-09-25 10:42:20
Also in:
linux-omap, linux-serial, lkml
Possibly related (same subject, not in this thread)
- 2014-09-29 · Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx · Sebastian Andrzej Siewior <bigeasy@linutronix.de>
- 2014-09-25 · Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx · Sebastian Andrzej Siewior <bigeasy@linutronix.de>
- 2014-09-22 · Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx · Heikki Krogerus <heikki.krogerus@linux.intel.com>
- 2014-09-19 · Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx · Peter Hurley <hidden>
- 2014-09-19 · Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx · Sebastian Andrzej Siewior <bigeasy@linutronix.de>
* Sebastian Andrzej Siewior | 2014-09-24 09:53:46 [+0200]:
* Peter Hurley | 2014-09-23 13:03:51 [-0400]:quoted
But DMA is cheating if the UART driver's tx_empty() method is saying the transmitter is empty while TX DMA is still running.This shouldn't be the case. But I will check this once I able to.
I added
|#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
| trace_printk("delay <%d>\n", (lsr & BOTH_EMPTY) == BOTH_EMPTY ? 1 : 0);
in my set_termios() and the trace shows
| vi-949 [000] d... 70.477002: omap8250_restore_regs: delay <0>
so no, it does not wait until TX FIFO is empty. It looks like it uses
TCSANOW instead of TCSADRAIN. And since this looks "legal" I will delay
it until TX-DMA is complete because it is known to stall the DMA operation.
quoted
Regards, Peter Hurley
Sebastian