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Date: Tue, 23 Sep 2014 13:03:51 -0400 From: Peter Hurley <peter@...leysoftware.com> To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Frans Klaver <frans.klaver@...ns.com> CC: Heikki Krogerus <heikki.krogerus@...ux.intel.com>, tony@...mide.com, gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org, balbi@...com, linux-serial@...r.kernel.org, linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, Alan Cox <alan@...ux.intel.com> Subject: Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx On 09/21/2014 04:41 PM, Sebastian Andrzej Siewior wrote: > * Frans Klaver | 2014-09-17 12:28:12 [+0200]: > >> - Bone Black: Yocto poky, core-image-minimal >> Login, "less file" locks up, doesn't show anything. I can exit using >> Ctrl-C. > > So I have the same with my and the serial-omap driver. No difference > here. The trace looks like this: > | <idle>-0 [000] d.h. 444.393585: serial8250_handle_irq: iir cc lsr 61 > | <idle>-0 [000] d.h. 444.393605: serial8250_rx_chars: get 0d > received the enter key > > | <idle>-0 [000] d.h. 444.393609: serial8250_rx_chars: insert d lsr 61 > | <idle>-0 [000] d.h. 444.393614: uart_insert_char: 1 > | <idle>-0 [000] d.h. 444.393617: uart_insert_char: 2 > | <idle>-0 [000] dnh. 444.393636: serial8250_tx_chars: empty > | kworker/0:2-753 [000] d... 444.393686: serial8250_start_tx: empty?1 > | kworker/0:2-753 [000] d.h. 444.393699: serial8250_handle_irq: iir c2 lsr 60 > | kworker/0:2-753 [000] d.h. 444.393705: serial8250_tx_chars: empty > | sh-1042 [000] d... 444.393822: serial8250_start_tx: empty?1 > | sh-1042 [000] d.h. 444.393836: serial8250_handle_irq: iir c2 lsr 60 > | sh-1042 [000] d.h. 444.393842: serial8250_tx_chars: empty > | sh-1042 [000] d... 444.393855: serial8250_start_tx: empty?0 > | sh-1042 [000] d.h. 444.393863: serial8250_handle_irq: iir c2 lsr 60 > | sh-1042 [000] d.h. 444.393867: serial8250_tx_chars: put 0d > | sh-1042 [000] d.h. 444.393871: serial8250_tx_chars: put 0a > > shell responded with "\r\n" which I see and then > > | sh-1042 [000] d.h. 444.394057: serial8250_handle_irq: iir c2 lsr 60 > | sh-1042 [000] d.h. 444.394065: serial8250_tx_chars: empty > > nothing more. less isn't sending data for some reason. Exactly the same > thing happens in a Debian environment except that it continues: > … > | bash-2468 [000] d.h. 99.657899: serial8250_tx_chars: put 0a > | bash-2468 [000] d.h. 99.658089: serial8250_handle_irq: iir c2 lsr 60 > | bash-2468 [000] d.h. 99.658095: serial8250_tx_chars: empty > => > | less-2474 [000] d... 99.696038: serial8250_start_tx: empty?0 > | less-2474 [000] d.h. 99.696069: serial8250_handle_irq: iir c2 lsr 60 > | less-2474 [000] d.h. 99.696078: serial8250_tx_chars: put 1b > | less-2474 [000] d.h. 99.696082: serial8250_tx_chars: put 5b > | less-2474 [000] d.h. 99.696085: serial8250_tx_chars: put 3f > | less-2474 [000] d.h. 99.696087: serial8250_tx_chars: put 31 > > It has to be something about the environment. Booting Debian and chroot > into this RFS and less works perfectly. But since it behaves like that > with both drivers, I guess the problem is somewhere else… > >> vi runs normally, only occupies part of the total screen estate in >> minicom. After quitting, a weird character shows up (typically I see >> ÿ there), but minicom can use the rest of the screen estate again. >> If we disregard the odd character, this is much like the behavior we >> have on the omap-serial driver. >> - Custom board: Yocto poky, custom image >> Login, "less file" locks up, showing only "ÿ" in the top left corner >> of the screen. Can get out of there by having something dumped through >> /dev/kmsg. > > I managed to run into something like that with vi on dra7 and with > little more patience on am335x as well by "vi *" and then ":n". > > This gets fixed indeed by writing. Hours of debugging and a lot of hair > less later: the yocto RFS calls set_termios quite a lot. readline() does this; it 'saves' the caller's termios, sets termios for non-canonical reads, reads one char, and 'restores' the caller's termios. > This includes > changing the baudrate (not by yocto but the driver sets it to 0 and then > to the requested one) and this seems to be responsible for the "bad > bytes". I haven't figured out yet I don't see this with omap-serial. > Even worse: If this (set_termios()) happens while the DMA is still > active then it might stall it. A write into the FIFO seems to fix it and > this is where your "echo >/dev/kmsg" fixes things. > If I delay the restore_registers part of set_termios() until TX-DMA is > complete then it seems that the TX-DMA stall does not tall anymore. The tty core calls the driver's wait_until_sent() method before changing the termios (if TCSADRAIN is used for tcsetattr(), which I think for readline() it does). But DMA is cheating if the UART driver's tx_empty() method is saying the transmitter is empty while TX DMA is still running. Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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