From: viresh kumar <viresh.kumar@st.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: "linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Linus WALLEIJ <linus.walleij@stericsson.com>,
Armando VISCONTI <armando.visconti@st.com>,
Shiraz HASHIM <shiraz.hashim@st.com>, amitgoel <amit.goel@st.com>,
"viresh.linux@gmail.com" <viresh.linux@gmail.com>,
"linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>
Subject: Re: [PATCH] tty/serial/pl011: don't print error msg if dmaengine_pause is not supported
Date: Tue, 19 Apr 2011 11:37:33 +0530 [thread overview]
Message-ID: <4DAD26A5.6080907@st.com> (raw)
In-Reply-To: <20110418151340.GB25671@n2100.arm.linux.org.uk>
On 04/18/2011 08:43 PM, Russell King - ARM Linux wrote:
> 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.
> .
>
Ok.
WARNING: multiple messages have this Message-ID (diff)
From: viresh.kumar@st.com (viresh kumar)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] tty/serial/pl011: don't print error msg if dmaengine_pause is not supported
Date: Tue, 19 Apr 2011 11:37:33 +0530 [thread overview]
Message-ID: <4DAD26A5.6080907@st.com> (raw)
In-Reply-To: <20110418151340.GB25671@n2100.arm.linux.org.uk>
On 04/18/2011 08:43 PM, Russell King - ARM Linux wrote:
> 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.
> .
>
Ok.
next prev parent reply other threads:[~2011-04-19 6:08 UTC|newest]
Thread overview: 8+ 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 11:22 ` Viresh Kumar
2011-04-18 15:13 ` Russell King - ARM Linux
2011-04-18 15:13 ` Russell King - ARM Linux
2011-04-19 6:07 ` viresh kumar [this message]
2011-04-19 6:07 ` viresh kumar
2011-04-19 0:27 ` Linus Walleij
2011-04-19 0:27 ` Linus Walleij
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