Am Donnerstag, den 20.09.2018, 08:39 +0000 schrieb Robin Gong:

quoted

-----Original Message-----
From: Uwe Kleine-König <redacted>
Sent: 2018年9月20日 15:55
To: Robin Gong <redacted>
Cc: jslaby@suse.com; Andy Duan <redacted>;
linux-serial@vger.kernel.org; linux-kernel@vger.kernel.org; dl-
linux-imx
[off-list ref]; kernel@pengutronix.de
Subject: Re: [PATCH v1] tty: serial: imx: enable IDDMAEN for the
last tail data

Hello,

On Thu, Sep 20, 2018 at 11:26:00PM +0800, Robin Gong wrote:

quoted

enable IDDMAEN in UCR4 to let sdma script has the chance to
detect the
idle status and transfer the last tail data with the interrupt
notifying uart driver.Otherwise, the last dma done interrupt of
the
tail data in rxfifo whose size is less than watermark may never
be
received by uart driver.

Is this a theoretic issue? Or does it fix a real problem?

If the former I'd say UCR1_ATDMAEN being set should prevent this
stall.

It's a real fix, you will see 'timeout We read 0 byte' with the
attached stress test
running on i.mx7d or i.mx6 if no this patch applied. 
' while [ 1 ]; do /unit_tests/UART/mxc_uart_stress_test.out
/dev/ttymxc5 2000000 D L 100 100 L; done &'
Please make sure dma enabled on ttymxcX for your test, and sdma
firmware setup in your rootfs 
/lib/firmware/imx/sdma/sdma-imx6q.bin or /lib/firmware/imx/sdma/sdma-
imx7d.bin.
You can get sdma firmware from below:
https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-
firmware.git/tree/imx/sdma

Please see commit 905c0decad28402aa166975023fb88c8f62f93c8 on why using
the idle detect together with with SDMA is wrong. We don't want to re-
introduce the broken behavior.

Regards,
Lucas