linux-kernel - regression: 3a878c430fd6 ("tty: serial: msm: Add TX DMA support") drops data

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Date:	Tue, 19 Apr 2016 16:23:29 -0700
From:	Frank Rowand <frowand.list@...il.com>
To:	ivan.ivanov@...aro.org
CC:	agross@...eaurora.org, David Brown <davidb@...eaurora.org>,
	srinivas.kandagatla@...aro.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	jslaby@...e.com, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	linux-soc@...r.kernel.org, linux-serial@...r.kernel.org
Subject: regression: 3a878c430fd6 ("tty: serial: msm: Add TX DMA support")
 drops data

Hi Ivan,

It appears that I have found a regression caused by
3a878c430fd6 ("tty: serial: msm: Add TX DMA support").

When I cat a file slightly larger than 126000 bytes on
the console, viewed via minicom connected to the serial
port, I am losing random chunks of data, almost always
three bytes in length.  I have also seen a lost chunk
of two bytes.

I am using the 8074 dragonboard, with the dts of
arch/arm/boot/dts/qcom-apq8074-dragonboard.dts.
The dts node is serial@...1e000, which has a
compatible of "qcom,msm-uartdm-v1.4", so is_uartdm
should be UARTDM_1P4.

Do you have any thoughts on what might be going
wrong, or what I can do to debug this?

Thanks,

Frank