Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756327AbbGVHdj (ORCPT ); Wed, 22 Jul 2015 03:33:39 -0400 Received: from mail-out.m-online.net ([212.18.0.9]:47578 "EHLO mail-out.m-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755276AbbGVHdf (ORCPT ); Wed, 22 Jul 2015 03:33:35 -0400 X-Auth-Info: 40PIrKPSHhsYC/2mnfFTyNSHhIE3nRIIvNY+k2BFzoA= From: Marek Vasut To: Michal Suchanek Subject: Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Date: Wed, 22 Jul 2015 09:33:19 +0200 User-Agent: KMail/1.13.7 (Linux/3.14-2-amd64; KDE/4.13.1; x86_64; ; ) Cc: Vinod Koul , Brian Norris , Richard Cochran , Geert Uytterhoeven , Mark Rutland , Krzysztof Kozlowski , Geert Uytterhoeven , MTD Maling List , Alison Chaiken , "Bean Huo =?utf-8?q?=E9=9C=8D=E6=96=8C=E6=96=8C?= (beanhuo)" , "linux-samsung-soc@vger.kernel.org" , Russell King , =?utf-8?q?Rafa=C5=82_Mi=C5=82ecki?= , 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 References: <20150722044925.GN23525@localhost> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Message-Id: <201507220933.19752.marex@denx.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2385 Lines: 52 On Wednesday, July 22, 2015 at 09:30:54 AM, Michal Suchanek wrote: > 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. This looks more like a signal integrity issue though. > 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 Best regards, Marek Vasut -- 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/