From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Viresh Kumar <viresh.kumar@st.com>
Cc: linux-arm-kernel@lists.infradead.org,
linus.walleij@stericsson.com, armando.visconti@st.com,
shiraz.hashim@st.com, amit.goel@st.com, viresh.linux@gmail.com,
linux-serial@vger.kernel.org
Subject: Re: [PATCH] tty/serial/pl011: don't print error msg if dmaengine_pause is not supported
Date: Mon, 18 Apr 2011 16:13:40 +0100 [thread overview]
Message-ID: <20110418151340.GB25671@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <98422bc7c3ebb4bf6a4ab26179b3f3b7d1a5b5ca.1303125086.git.viresh.kumar@st.com>
On Mon, Apr 18, 2011 at 04:52:00PM +0530, Viresh Kumar wrote:
> Few dma controller doesn't support dmaengine_pause() and return -ENXIO if
> dmaengine_pause() is called for them. Error messages such as "unable to pause
> DMA transfer" shouldn't be printed for them.
It is _required_ to pause the DMA engine at this point, as we need to
read characters via PIO. Leaving the DMA engine active at this point
invites it to transfer additional characters beneath us, before we've
had time to properly update the DMA engine for the characters received.
So, dmaengine_pause() is a requirement for PL011.
next prev parent reply other threads:[~2011-04-18 15:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-18 11:22 [PATCH] tty/serial/pl011: don't print error msg if dmaengine_pause is not supported Viresh Kumar
2011-04-18 15:13 ` Russell King - ARM Linux [this message]
2011-04-19 6:07 ` viresh kumar
2011-04-19 0:27 ` Linus Walleij
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