From mboxrd@z Thu Jan 1 00:00:00 1970 From: Piotr =?iso-8859-1?Q?Kr=F3l?= Subject: Re: amba-pl011 complains about DMA for bcm2835 where it is not supported Date: Tue, 28 Oct 2014 01:09:23 +0100 Message-ID: <20141028000922.GB1788@haysend> References: <20141027234430.GA1788@haysend> <20141027235942.GY27405@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from az0017.srv.az.pl ([46.242.145.17]:43479 "EHLO az0017.srv.az.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753108AbaJ1AJ1 (ORCPT ); Mon, 27 Oct 2014 20:09:27 -0400 Content-Disposition: inline In-Reply-To: <20141027235942.GY27405@n2100.arm.linux.org.uk> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Russell King - ARM Linux Cc: linux-serial@vger.kernel.org, jslaby@suse.cz, gregkh@linuxfoundation.org On Mon, Oct 27, 2014 at 11:59:42PM +0000, Russell King - ARM Linux wrot= e: > On Tue, Oct 28, 2014 at 12:44:31AM +0100, Piotr Kr=F3l wrote: > > Hi all, > > according to BCM2835 ARM Peripherals spec DMA is optional functiona= lity > > for ARM PL011 UART and it is not supported on this SoC. It looks li= ke > > amba-pl011 search for device tree property (dma-names) unconditiona= lly, > > what leads to error message: > >=20 > > of_dma_request_slave_channel: dma-names property of node '/soc/uart= @7e201000' missing or empty > > uart-pl011 20201000.uart: no DMA platform data > >=20 > > 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. I= s > > there any known method for checking dma support ? If yes that I wou= ld be > > glad for any pointers. > >=20 > > Let me know if I should ignore/accept this error message or there i= s > > some code fix needed. >=20 > A great many implementations of PL011 do not have DMA support (some h= ave > DMA support but its well broken.) The driver has always supported PI= O > mode, and continues to do so. >=20 Driver works fine but IMHO this error message confuse user. Should I as= sume that error message is expected and we should not avoid it by trying to check if DMA is supported ? BTW above error message do not indicate that DMA is not supported but indicates that something is wrong with DT, what in this case is not tru= e. Thanks, Piotr Kr=F3l -- To unsubscribe from this list: send the line "unsubscribe linux-serial"= in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html