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Message-ID: <20141013145534.GB25389@ci00147.xsens-tech.local>
Date: Mon, 13 Oct 2014 16:55:34 +0200
From: Frans Klaver <frans.klaver@...ns.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC: Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
Peter Hurley <peter@...leysoftware.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 Thu, Oct 02, 2014 at 12:27:23PM +0200, Sebastian Andrzej Siewior wrote:
> * Frans Klaver | 2014-09-30 10:44:16 [+0200]:
>
> > uart_test-483 [000] dnh. 17.861018: serial8250_interrupt: irq 89
> > uart_test-483 [000] dnh. 17.861026: serial8250_interrupt: 89 e
> e? Did was the routine invoked 0xe times or this a register?
No, this marks the end of serial8250_interrupt().
> > uart_test-479 [000] d.H. 17.861124: serial8250_interrupt: irq 89
> > uart_test-479 [000] d.H. 17.861133: serial8250_handle_irq: l1 IIR cc LSR 61
> > uart_test-479 [000] d.H. 17.861135: serial8250_handle_irq: rx_dma(up, iir)
> > uart_test-479 [000] d.H. 17.861139: serial8250_rx_dma: l1, UART_IIR_RX_TIMEOUT
> > uart_test-479 [000] d.H. 17.861147: __dma_rx_do_complete: error: 1, uart_bug_dma: 32
> > uart_test-479 [000] d.H. 17.861150: serial8250_handle_irq: rx_chars(up, status)
> > uart_test-479 [000] d.H. 17.861190: serial8250_handle_irq: rx_dma(up, 0)
> timeout, manual purge. Do you have an idea how many bytes were manually
> received?
Here's an excerpt from a new trial using v10
(previous was v10_pre3). We manually read 10 bytes before we start
trying to get all bytes without dma.
uart_test-483 [000] dnH. 18.182647: serial8250_interrupt: irq 89
uart_test-483 [000] dnH. 18.182653: omap_8250_dma_handle_irq: rx_dma(up, iir)
uart_test-483 [000] dnH. 18.182655: omap_8250_rx_dma: UART_IIR_RX_TIMEOUT
uart_test-483 [000] dnH. 18.182657: omap_8250_rx_dma: rx was running
uart_test-483 [000] dnH. 18.182662: __dma_rx_do_complete: count = 0
uart_test-483 [000] dnH. 18.182666: omap_8250_dma_handle_irq: rx_chars(up, status)
uart_test-483 [000] dnH. 18.182683: serial8250_rx_chars: bytes read = 10
uart_test-483 [000] dnH. 18.182685: omap_8250_dma_handle_irq: rx_dma(up, 0)
uart_test-483 [000] dnH. 18.182698: omap_8250_dma_handle_irq: rpm_put(up)
uart_test-483 [000] dnH. 18.182701: serial8250_interrupt: 89 end
uart_test-488 [000] ..s. 18.185353: __dma_rx_do_complete: count = 48
uart_test-488 [000] ..s. 18.185366: __dma_rx_do_complete: rx_dma(p, 0)
kworker/0:1-10 [000] d.H. 18.185486: serial8250_interrupt: irq 89
kworker/0:1-10 [000] d.H. 18.185496: omap_8250_dma_handle_irq: rpm_put(up)
kworker/0:1-10 [000] d.H. 18.185501: serial8250_interrupt: 89 end
kworker/0:1-10 [000] ..s. 18.185520: __dma_rx_do_complete: count = 48
kworker/0:1-10 [000] ..s. 18.185526: __dma_rx_do_complete: rx_dma(p, 0)
Below things go downhill again.
kworker/0:1-10 [000] ..s. 18.227273: __dma_rx_do_complete: rx_dma(p, 0)
uart_test-483 [000] ..s. 18.227396: __dma_rx_do_complete: count = 48
uart_test-483 [000] ..s. 18.227404: __dma_rx_do_complete: rx_dma(p, 0)
uart_test-485 [000] .ns. 18.227540: __dma_rx_do_complete: count = 48
uart_test-485 [000] .ns. 18.227547: __dma_rx_do_complete: rx_dma(p, 0)
kworker/0:2-65 [000] ..s. 18.227660: __dma_rx_do_complete: count = 48
kworker/0:2-65 [000] ..s. 18.227667: __dma_rx_do_complete: rx_dma(p, 0)
kworker/0:1-10 [000] .ns. 18.227786: __dma_rx_do_complete: count = 48
kworker/0:1-10 [000] .ns. 18.227793: __dma_rx_do_complete: rx_dma(p, 0)
uart_test-477 [000] ..s. 18.227921: __dma_rx_do_complete: count = 48
uart_test-477 [000] ..s. 18.227928: __dma_rx_do_complete: rx_dma(p, 0)
uart_test-481 [000] ..s. 18.228051: __dma_rx_do_complete: count = 48
uart_test-481 [000] ..s. 18.228057: __dma_rx_do_complete: rx_dma(p, 0)
kworker/0:1-10 [000] ..s. 18.228185: __dma_rx_do_complete: count = 48
kworker/0:1-10 [000] ..s. 18.228191: __dma_rx_do_complete: rx_dma(p, 0)
uart_test-485 [000] ..s. 18.228318: __dma_rx_do_complete: count = 48
uart_test-485 [000] ..s. 18.228324: __dma_rx_do_complete: rx_dma(p, 0)
uart_test-488 [000] d.h. 18.228445: serial8250_interrupt: irq 89
uart_test-488 [000] d.h. 18.228454: omap_8250_dma_handle_irq: rpm_put(up)
uart_test-488 [000] d.h. 18.228459: serial8250_interrupt: 89 end
uart_test-488 [000] d.H. 18.228472: serial8250_interrupt: irq 89
uart_test-488 [000] d.H. 18.228477: omap_8250_dma_handle_irq: rx_dma(up, iir)
uart_test-488 [000] d.H. 18.228479: omap_8250_rx_dma: UART_IIR_RX_TIMEOUT
uart_test-488 [000] d.H. 18.228480: omap_8250_rx_dma: rx was running
uart_test-488 [000] d.H. 18.228487: __dma_rx_do_complete: count = 48
uart_test-488 [000] d.H. 18.228500: omap_8250_dma_handle_irq: rx_chars(up, status)
uart_test-488 [000] d.H. 18.228517: serial8250_rx_chars: bytes read = 10
uart_test-488 [000] d.H. 18.228519: omap_8250_dma_handle_irq: rx_dma(up, 0)
uart_test-488 [000] d.H. 18.228534: omap_8250_dma_handle_irq: rpm_put(up)
uart_test-488 [000] d.H. 18.228540: serial8250_interrupt: 89 end
kworker/0:1-10 [000] dnh. 18.234930: serial8250_interrupt: irq 89
kworker/0:1-10 [000] dnh. 18.235074: omap_8250_dma_handle_irq: rx_dma(up, iir)
kworker/0:1-10 [000] dnh. 18.235123: omap_8250_rx_dma: UART_IIR_RX_TIMEOUT
kworker/0:1-10 [000] dnh. 18.235159: omap_8250_rx_dma: rx was running
kworker/0:1-10 [000] dnh. 18.235334: __dma_rx_do_complete: count = 48
kworker/0:1-10 [000] dnh. 18.235455: omap_8250_dma_handle_irq: rx_chars(up, status)
kworker/0:1-10 [000] dnh. 18.238523: serial8250_rx_chars: bytes read = 256
kworker/0:1-10 [000] dnh. 18.238566: omap_8250_dma_handle_irq: rx_dma(up, 0)
kworker/0:1-10 [000] dnh. 18.239169: omap_8250_dma_handle_irq: rx_dma(up, iir)
kworker/0:1-10 [000] dnh. 18.239223: omap_8250_rx_dma: UART_IIR_RX_TIMEOUT
kworker/0:1-10 [000] dnh. 18.239256: omap_8250_rx_dma: rx was running
kworker/0:1-10 [000] dnh. 18.239377: __dma_rx_do_complete: count = 0
kworker/0:1-10 [000] dnh. 18.239449: omap_8250_dma_handle_irq: rx_chars(up, status)
kworker/0:1-10 [000] dnh. 18.242576: serial8250_rx_chars: bytes read = 256
kworker/0:1-10 [000] dnh. 18.242620: omap_8250_dma_handle_irq: rx_dma(up, 0)
kworker/0:1-10 [000] dnh. 18.242878: omap_8250_dma_handle_irq: rx_dma(up, iir)
kworker/0:1-10 [000] dnh. 18.242921: omap_8250_rx_dma: UART_IIR_RX_TIMEOUT
kworker/0:1-10 [000] dnh. 18.242954: omap_8250_rx_dma: rx was running
kworker/0:1-10 [000] dnh. 18.243064: __dma_rx_do_complete: count = 0
kworker/0:1-10 [000] dnh. 18.243127: omap_8250_dma_handle_irq: rx_chars(up, status)
kworker/0:1-10 [000] dnh. 18.246238: serial8250_rx_chars: bytes read = 256
kworker/0:1-10 [000] dnh. 18.246283: omap_8250_dma_handle_irq: rx_dma(up, 0)
kworker/0:1-10 [000] dnh. 18.246524: omap_8250_dma_handle_irq: rx_dma(up, iir)
kworker/0:1-10 [000] dnh. 18.246563: omap_8250_rx_dma: UART_IIR_RX_TIMEOUT
kworker/0:1-10 [000] dnh. 18.246599: omap_8250_rx_dma: rx was running
kworker/0:1-10 [000] dnh. 18.246702: __dma_rx_do_complete: count = 0
> > kworker/0:1-10 [000] dnH. 20.027093: serial8250_interrupt: serial8250: too much work for irq89
> > kworker/0:1-10 [000] dnH. 20.027181: serial8250_interrupt: 89 e
> >
> >This clogs the entire system until I disconnect the communication lines.
> >
> >So we get an RX timeout. The receiver fifo trigger level was not reached
> >and 8250_core is left to copy the remaining data. I would expect that if
> >the trigger level wasn't reached, we wouldn't need to be doing this that
> >often. On the other hand, could we be trapped reading data from rx
> >without dma helping us? And how could we resolve this?
>
> So if I understand you correct, then you enter serial8250_interrupt()
> and then you enter multiple times omap_8250_dma_handle_irq() and
> you always get a TIMEOUT event and fetch byte(s) manualy via
> serial8250_rx_chars(). And after one iteration UART_IIR_NO_INT is not
> set and you do it again, right?
That's what it looks like, yes.
> I have no idea when exactly the timeout-interrupt fires. The manual
> says: "… the count is reset when there is activity on uarti_rx …" but it
> does not say how often it increments before the level is reached.
> It also might be that you have a small gap between two bytes and this
> high baud rate the gap is considered as a timeout event.
>
> Another thing could be that if the we enqueue a RX transfer from the
> dma_completion callback then we have too many bytes in the FIFO already
> becahse the callback is invoked from softirq. What happens if we cut the
> middle man via
>
>
> diff --git a/drivers/dma/virt-dma.c b/drivers/dma/virt-dma.c
> index 6f80432..21b04bd 100644
> --- a/drivers/dma/virt-dma.c
> +++ b/drivers/dma/virt-dma.c
> @@ -63,8 +63,9 @@ static void vchan_complete(unsigned long arg)
> dma_async_tx_callback cb = NULL;
> void *cb_data = NULL;
> LIST_HEAD(head);
> + unsigned long flags;
>
> - spin_lock_irq(&vc->lock);
> + spin_lock_irqsave(&vc->lock, flags);
> list_splice_tail_init(&vc->desc_completed, &head);
> vd = vc->cyclic;
> if (vd) {
> @@ -72,7 +73,7 @@ static void vchan_complete(unsigned long arg)
> cb = vd->tx.callback;
> cb_data = vd->tx.callback_param;
> }
> - spin_unlock_irq(&vc->lock);
> + spin_unlock_irqrestore(&vc->lock, flags);
>
> if (cb)
> cb(cb_data);
> diff --git a/drivers/dma/virt-dma.h b/drivers/dma/virt-dma.h
> index 181b952..7632338 100644
> --- a/drivers/dma/virt-dma.h
> +++ b/drivers/dma/virt-dma.h
> @@ -92,7 +92,10 @@ static inline void vchan_cookie_complete(struct virt_dma_desc *vd)
> vd, cookie);
> list_add_tail(&vd->node, &vc->desc_completed);
>
> - tasklet_schedule(&vc->task);
> + if (vd->tx.my_uart)
> + vc->task.func(vc);
> + else
> + tasklet_schedule(&vc->task);
> }
>
> /**
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index 57a8b12..5d7ee92 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -728,6 +728,7 @@ static int omap_8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
> dma->rx_running = 1;
> desc->callback = __dma_rx_complete;
> desc->callback_param = p;
> + desc->my_uart = 1;
>
> dma->rx_cookie = dmaengine_submit(desc);
>
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 1f9e642..0f5fbe1 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -459,6 +459,7 @@ struct dmaengine_unmap_data {
> struct dma_async_tx_descriptor {
> dma_cookie_t cookie;
> enum dma_ctrl_flags flags; /* not a 'long' to pack with cookie */
> + u32 my_uart;
> dma_addr_t phys;
> struct dma_chan *chan;
> dma_cookie_t (*tx_submit)(struct dma_async_tx_descriptor *tx);
>
[ 251.363111] BUG: spinlock recursion on CPU#0, swapper/0
[ 251.368394] lock: 0xcf151dc4, .magic: dead4ead, .owner: swapper/0, .owner_cpu: 0
[ 251.375920] CPU: 0 PID: 0 Comm: swapper Not tainted 3.17.0-rc5-00141-geccc467-dirty #35
[ 251.384012] [<c0013454>] (unwind_backtrace) from [<c00113b0>] (show_stack+0x10/0x14)
[ 251.391811] [<c00113b0>] (show_stack) from [<c0055cdc>] (do_raw_spin_lock+0x48/0x110)
[ 251.399703] [<c0055cdc>] (do_raw_spin_lock) from [<c04dbef0>] (_raw_spin_lock_irqsave+0x10/0x18)
[ 251.408544] [<c04dbef0>] (_raw_spin_lock_irqsave) from [<c0221f74>] (vchan_complete+0x1c/0xe8)
[ 251.417207] [<c0221f74>] (vchan_complete) from [<c0222f54>] (edma_callback+0x138/0x274)
[ 251.425259] [<c0222f54>] (edma_callback) from [<c001a844>] (dma_irq_handler+0x154/0x190)
[ 251.433406] [<c001a844>] (dma_irq_handler) from [<c005b2dc>] (handle_irq_event_percpu+0x2c/0x130)
[ 251.442331] [<c005b2dc>] (handle_irq_event_percpu) from [<c005b41c>] (handle_irq_event+0x3c/0x5c)
[ 251.451254] [<c005b41c>] (handle_irq_event) from [<c005d940>] (handle_level_irq+0xd0/0x108)
[ 251.459655] [<c005d940>] (handle_level_irq) from [<c005acc0>] (generic_handle_irq+0x20/0x30)
[ 251.468144] [<c005acc0>] (generic_handle_irq) from [<c000ee2c>] (handle_IRQ+0x60/0x80)
[ 251.476109] [<c000ee2c>] (handle_IRQ) from [<c0008654>] (omap3_intc_handle_irq+0x64/0x8c)
[ 251.484337] [<c0008654>] (omap3_intc_handle_irq) from [<c0011dc0>] (__irq_svc+0x40/0x54)
[ 251.492466] Exception stack(0xc0725f68 to 0xc0725fb0)
[ 251.497549] 5f60: 00000000 c0757160 00000000 c0018fc0 c0724000 c0724038
[ 251.505772] 5f80: c078de40 c072c040 c0714124 cfefc4c0 00000000 00000000 c0757160 c0725fb0
[ 251.513989] 5fa0: c000ef40 c000ef44 60000013 ffffffff
[ 251.519077] [<c0011dc0>] (__irq_svc) from [<c000ef44>] (arch_cpu_idle+0x2c/0x38)
[ 251.526517] [<c000ef44>] (arch_cpu_idle) from [<c005255c>] (cpu_startup_entry+0x9c/0xf0)
[ 251.534664] [<c005255c>] (cpu_startup_entry) from [<c06e5b34>] (start_kernel+0x308/0x360)
I should probably take out the spin_lock calls if vd->tx.my_uart is 1?
Thanks,
Frans
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