Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932946AbbGVHbk (ORCPT ); Wed, 22 Jul 2015 03:31:40 -0400 Received: from mail-wi0-f174.google.com ([209.85.212.174]:33750 "EHLO mail-wi0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756258AbbGVHbf (ORCPT ); Wed, 22 Jul 2015 03:31:35 -0400 MIME-Version: 1.0 In-Reply-To: <20150722044925.GN23525@localhost> References: <20150604171547.GA1530@localhost.localdomain> <201507151352.27689.marex@denx.de> <20150715155946.GB21362@localhost> <20150721042932.GF23525@localhost> <20150722044925.GN23525@localhost> From: Michal Suchanek Date: Wed, 22 Jul 2015 09:30:54 +0200 Message-ID: Subject: Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. To: Vinod Koul Cc: Brian Norris , Marek Vasut , Richard Cochran , Geert Uytterhoeven , Mark Rutland , Krzysztof Kozlowski , Geert Uytterhoeven , MTD Maling List , Alison Chaiken , =?UTF-8?B?QmVhbiBIdW8g6ZyN5paM5paMIChiZWFuaHVvKQ==?= , "linux-samsung-soc@vger.kernel.org" , Russell King , =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= , Kukjin Kim , Ben Hutchings , "devicetree@vger.kernel.org" , Pawel Moll , Ian Campbell , Kumar Gala , Mark Brown , Dan Williams , "linux-arm-kernel@lists.infradead.org" , "grmoore@altera.com" , "linux-kernel@vger.kernel.org" , linux-spi , Huang Shijie , Rob Herring , Han Xu , Knut Wohlrab , dmaengine , David Woodhouse Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2148 Lines: 45 On 22 July 2015 at 06:49, Vinod Koul wrote: > On Tue, Jul 21, 2015 at 10:14:11AM +0200, Michal Suchanek wrote: >> > Or alternatively we could publish the limitations of the channel using >> > capabilities so SPI knows I have a dmaengine channel and it can transfer max N >> > length transfers so would be able to break rather than guessing it or coding >> > in DT. Yes it may come from DT but that should be dmaengine driver rather >> > than client driver :) >> > >> > This can be done by dma_get_slave_caps(chan, &caps) >> > >> > And we add max_length as one more parameter to existing set >> > >> > Also all this could be handled in generic SPI-dmaengine layer so that >> > individual drivers don't have to code it in >> > >> > Let me know if this idea is okay, I can push the dmaengine bits... >> >> It would be ok if there was a fixed limit. However, the limit depends >> on SPI slave settings. Presumably for other buses using the dmaengine >> the limit would depend on the bus or slave settings as well. I do not >> see a sane way of passing this all the way to the dmaengine driver. > I don't see why this should be client (SPI) dependent. The max length > supported is a dmaengine constraint, typically flowing from max > blocks/length it can transfer. Know this limit can allow clients to split > transfers. In practice on the board I have the maximum transfer length before it fails depends on SPI bus speed which is set up per slave. I did not try searching the space of possible settings thorougly and settled for a setting that gives reasonable speed and transfer length. However, if this was not tied to the particular slave setting picked in the current DT a formula would be needed that translates arbitrary client settings to transfer size limit and there would be need to somehow get the client settings to the formula in the dmaengine driver. Thanks Michal -- 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/