From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: "Piotr Król" <piotr.krol@3mdeb.com>
Cc: linux-serial@vger.kernel.org, jslaby@suse.cz, gregkh@linuxfoundation.org
Subject: Re: amba-pl011 complains about DMA for bcm2835 where it is not supported
Date: Mon, 27 Oct 2014 23:59:42 +0000 [thread overview]
Message-ID: <20141027235942.GY27405@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <20141027234430.GA1788@haysend>
On Tue, Oct 28, 2014 at 12:44:31AM +0100, Piotr Król wrote:
> Hi all,
> according to BCM2835 ARM Peripherals spec DMA is optional functionality
> for ARM PL011 UART and it is not supported on this SoC. It looks like
> amba-pl011 search for device tree property (dma-names) unconditionally,
> what leads to error message:
>
> of_dma_request_slave_channel: dma-names property of node '/soc/uart@7e201000' missing or empty
> uart-pl011 20201000.uart: no DMA platform data
>
> I assume that if it is possible that amba-pl011 can be without DMA we
> should check if DMA is supported and then try to read properties. Is
> there any known method for checking dma support ? If yes that I would be
> glad for any pointers.
>
> Let me know if I should ignore/accept this error message or there is
> some code fix needed.
A great many implementations of PL011 do not have DMA support (some have
DMA support but its well broken.) The driver has always supported PIO
mode, and continues to do so.
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next prev parent reply other threads:[~2014-10-27 23:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-27 23:44 amba-pl011 complains about DMA for bcm2835 where it is not supported Piotr Król
2014-10-27 23:59 ` Russell King - ARM Linux [this message]
2014-10-28 0:09 ` Piotr Król
2014-10-28 0:16 ` Russell King - ARM Linux
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