linux-kernel - Re: [PATCH] serial: imx: Revert "initialized DMA w/o HW flow enabled"

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Date:	Thu, 7 May 2015 17:54:31 -0300
From:	Fabio Estevam <festevam@...il.com>
To:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	jiwang <jiada_wang@...tor.com>, Jiri Slaby <jslaby@...e.cz>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	anton_bondarenko@...tor.com, Dirk Behme <dirk.behme@...bosch.com>,
	Nicolae Rosia <nicolae.rosia@...il.com>,
	Fabio Estevam <fabio.estevam@...escale.com>
Subject: Re: [PATCH] serial: imx: Revert "initialized DMA w/o HW flow enabled"

On Thu, May 7, 2015 at 5:24 PM, Sebastian Andrzej Siewior
<sebastian@...akpoint.cc> wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
>
> This basically reverts commit 068500e08dc8 ("serial: imx: initialized
> DMA w/o HW flow enabled") simply because it does not work as expected
> without additional magic which I am not aware of. The DMA mode is only
> used for non-console UARTs so the "standard" boot test won't notice this.
>
> I tested it on various IMX6 (S and Q) boards and the default SDMA firmware
> that is included in ROM does work properly. The SDMA interrupt counter does
> not stop increment (which means the SDMA does not stop working or the ACK
> is working) and I see a lot of 0x00 (sometimes other bytes) which are added
> to the tty buffer which are not part of the data transfer.
> Jiada claimed that there is a firmware which makes it work but failed to
> provide me a link to the firmware. All he said was that it can not be
> shipped as part of the kernel due to license issues. I've found a firmware
> blob in the FSL-tree but this firmware causes only TTY-overflows an *no*
> data is transmitted.
>
> Currently I see no other way out.
>
> Fixes: 068500e08dc8 ("serial: imx: initialized DMA w/o HW flow enabled")
> Cc: Fabio Estevam <fabio.estevam@...escale.com>
> Cc: Jiada Wang <jiada_wang@...tor.com>
> Cc: nicolae.rosia@...il.com
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Thanks, this fixes Bluetooth operation on a imx6sl-warp running
without SDMA firmware.

Two suggestions:

1. You should Cc stable as it affects 4.0 also

2. It doesn't apply cleanly against linux-next, so I think Greg will
have problems applying it.
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