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Date: Tue, 15 Sep 2015 14:42:45 +0200
From: Robert Baldyga <r.baldyga@...sung.com>
To: Krzysztof Kozlowski <k.kozlowski@...sung.com>,
gregkh@...uxfoundation.org
Cc: jslaby@...e.com, linux-serial@...r.kernel.org,
linux-kernel@...r.kernel.org, m.szyprowski@...sung.com
Subject: Re: [PATCH v2 3/4] serial: samsung: introduce
s3c24xx_serial_rx_drain_fifo() function
On 09/11/2015 08:15 AM, Krzysztof Kozlowski wrote:
> On 10.09.2015 22:41, Robert Baldyga wrote:
>> This patch introduces s3c24xx_serial_rx_drain_fifo() which reads data
>> from RX FIFO and writes it to tty buffer. It also checks for special
>> conditions (such as 'break') and handles it. This function has been
>> separated from s3c24xx_serial_rx_chars_pio() as it contains code which
>> can be used also in DMA mode.
>
> Much better, thanks! Now it is also easier to spot the difference (see
> below).
>
>>
>> Signed-off-by: Robert Baldyga <r.baldyga@...sung.com>
>> ---
>> drivers/tty/serial/samsung.c | 23 +++++++++++++----------
>> 1 file changed, 13 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c
>> index dc4be54..1d7dd86 100644
>> --- a/drivers/tty/serial/samsung.c
>> +++ b/drivers/tty/serial/samsung.c
>> @@ -621,16 +621,12 @@ finish:
>> return IRQ_HANDLED;
>> }
>>
>> -static irqreturn_t s3c24xx_serial_rx_chars_pio(void *dev_id)
>> +static void s3c24xx_serial_rx_drain_fifo(struct s3c24xx_uart_port *ourport)
>> {
>> - struct s3c24xx_uart_port *ourport = dev_id;
>> struct uart_port *port = &ourport->port;
>> unsigned int ufcon, ch, flag, ufstat, uerstat;
>> - unsigned long flags;
>> int max_count = port->fifosize;
>>
>> - spin_lock_irqsave(&port->lock, flags);
>> -
>> while (max_count-- > 0) {
>> ufcon = rd_regl(port, S3C2410_UFCON);
>> ufstat = rd_regl(port, S3C2410_UFSTAT);
>> @@ -654,9 +650,7 @@ static irqreturn_t s3c24xx_serial_rx_chars_pio(void *dev_id)
>> ufcon |= S3C2410_UFCON_RESETRX;
>> wr_regl(port, S3C2410_UFCON, ufcon);
>> rx_enabled(port) = 1;
>> - spin_unlock_irqrestore(&port->lock,
>> - flags);
>> - goto out;
>> + return;
>> }
>> continue;
>> }
>> @@ -702,10 +696,19 @@ static irqreturn_t s3c24xx_serial_rx_chars_pio(void *dev_id)
>> ch, flag);
>> }
>>
>> - spin_unlock_irqrestore(&port->lock, flags);
>> tty_flip_buffer_push(&port->state->port);
>
> Here is a difference - previously this was outside of spinlock. I think
> moving it inside spin lock is okay, just the interrupts won't be
> disabled before unlock and queue_work() from tty_flip_buffer_push().
>
> However after testing this patchset (entire) on:
> next-20150910 + my dt-for-next branch (dma for serial) + this patchset
> you can see quite complicated lockdep warning:
>
> [ 3.568657] =========================================================
> [ 3.575079] [ INFO: possible irq lock inversion dependency detected ]
> [ 3.581506] 4.2.0-next-20150910-00009-g65fd5a9cff54 #218 Not tainted
> [ 3.587838] ---------------------------------------------------------
> [ 3.594263] swapper/0/0 just changed the state of lock:
> [ 3.599470] (&port_lock_key){..-...}, at: [<c02a8fac>]
> s3c24xx_serial_tx_dma_complete+0x8c/0xfc
> [ 3.608237] but this lock took another, SOFTIRQ-unsafe lock in the past:
> [ 3.614919] (&(&ctx->lock)->rlock){+.+...}
> [ 3.614919]
> [ 3.614919] and interrupts could create inverse lock ordering between
> them.
> [ 3.614919]
> [ 3.625076]
> [ 3.625076] other info that might help us debug this:
> [ 3.631586] Possible interrupt unsafe locking scenario:
> [ 3.631586]
> [ 3.638356] CPU0 CPU1
> [ 3.642870] ---- ----
> [ 3.647382] lock(&(&ctx->lock)->rlock);
> [ 3.651376] local_irq_disable();
> [ 3.657278] lock(&port_lock_key);
> [ 3.663267] lock(&(&ctx->lock)->rlock);
> [ 3.669777] <Interrupt>
> [ 3.672381] lock(&port_lock_key);
>
>
> Config: exynos, disabled MMC_CLKGATE, enabled usual testing stuff
> Board: Trats2
>
> Didn't you notice it?
>
>
> Additionally the SysRq "Show backtrace of all active CPUs" on this
> linux-next (without additional patches, pure next) has significant delay
> (like 5 seconds) and a:
> [ 169.221223] s3c-i2c 138d0000.i2c: timeout waiting for bus idle
>
> That's weird. But as I said this occurs on pure next as well.
>
I've noticed that commit [1] reveals the problem, but in result of git
bisect (at each step I was applying [1]) I got:
d71fc239b6915a8b750e9a447311029ff45b6580 is the first bad commit
That points to [2], which looks strange to me. However bug seems to be
unrelated to my patches, so I will send v3 soon.
[1] commit: 22374fbedb2ce03ef81323b3f7ceb3fa29344aa6
"ARM: dts: Add DMA support for serial ports in exynos4"
[2] commit: d71fc239b6915a8b750e9a447311029ff45b6580
"Merge tag 'armsoc-late' of
git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc"
Best regards,
Robert Baldyga
>
>> +}
>> +
>> +static irqreturn_t s3c24xx_serial_rx_chars_pio(void *dev_id)
>> +{
>> + struct s3c24xx_uart_port *ourport = dev_id;
>> + struct uart_port *port = &ourport->port;
>> + unsigned long flags;
>> +
>> + spin_lock_irqsave(&port->lock, flags);
>> + s3c24xx_serial_rx_drain_fifo(ourport);
>> + spin_unlock_irqrestore(&port->lock, flags);
>>
>> -out:
>> return IRQ_HANDLED;
>> }
>>
>>
>
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