Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753018Ab1FNF7e (ORCPT ); Tue, 14 Jun 2011 01:59:34 -0400 Received: from mail-wy0-f174.google.com ([74.125.82.174]:37244 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750886Ab1FNF7a (ORCPT ); Tue, 14 Jun 2011 01:59:30 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; b=i/i0cIIVpBR1dr97UOpBh+TU1C/V/JeCxQcO04ggwMJ1LKaI+S4ZpApoJNf8IwQck9 Wh1wZXK8GaonSkUM1RKGqfbfI4yTemQP8hLrPXZL8f4B6iXi+wqhgwg7DVp3MX+RYOwo b+CEo/R6HchtkQ5OwsOmqiCA0tg2MIxOBGo7E= MIME-Version: 1.0 In-Reply-To: References: <20110609124723.GA24636@n2100.arm.linux.org.uk> <20110609163206.GB24636@n2100.arm.linux.org.uk> <1307686397.10976.116.camel@vkoul-udesk3> <20110610104318.GC24636@n2100.arm.linux.org.uk> <20110610133338.GD24636@n2100.arm.linux.org.uk> Date: Tue, 14 Jun 2011 07:59:29 +0200 X-Google-Sender-Auth: 9eIbyxe0LqpxRUYGMwttAVV8010 Message-ID: Subject: Re: [RFC] dmaengine: add new api for preparing simple slave transfer From: Linus Walleij To: "Raju, Sundaram" Cc: "davinci-linux-open-source@linux.davincidsp.com" , Russell King - ARM Linux , "Koul, Vinod" , "linux-kernel@vger.kernel.org" , Dan , "linux-omap@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1362 Lines: 34 2011/6/14 Raju, Sundaram : > Yes, the hardware can skip over sequences like that. > I also thought about your suggestion, at first before submitting the RFC. > But I dint pursue this because, this ioctl() call has to be made before > every single prepare call. It's not an ioctl(), ioctl()s would be expensive since they involve userspace to kernelspace context switches. It is just "ioctl()-like". It is a simple, fast function call. > I may have to end up using this if we decide not to change the API > signature for prepare APIs. Is it really so bad? It is a custom configuration after all. Even if there were many DMACs out there supporting it, we'd probably model it like this, just pass something like DMA_STRIDE_CONFIG instead of something named after a specific slave controller. This way DMACs that didn't support striding could NACK a transfer for device drivers requesting it and then it could figure out what to do. If we can get some indication as to whether more DMACs can do this kind of stuff, we'd maybe like to introduce DMA_STRIDE_CONFIG already now. Thanks, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/