Messages in this thread | | | Date | Thu, 25 Sep 2014 07:31:32 -0400 | From | Peter Hurley <> | Subject | Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx |
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On 09/25/2014 06:42 AM, Sebastian Andrzej Siewior wrote: > * Sebastian Andrzej Siewior | 2014-09-24 09:53:46 [+0200]: > >> * Peter Hurley | 2014-09-23 13:03:51 [-0400]: >> >>> 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.
I just verified that GNU readline6 uses ioctl(TCSETSW, ...) to do the set_termios (which is the ioctl that libc should use for tcsetattr(TCSADRAIN)).
Maybe this userspace is using a readline()-alike that has a bug by not using the correct tcsetattr() action? Or maybe the glibc-equivalent has the bug, and tcsetattr(TCSADRAIN) is not using ioctl(TCSETSW)?
Regards, Peter Hurley
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