From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vinod Koul Subject: Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Date: Wed, 22 Jul 2015 10:19:25 +0530 Message-ID: <20150722044925.GN23525@localhost> References: <20150604171547.GA1530@localhost.localdomain> <201507151352.27689.marex@denx.de> <20150715155946.GB21362@localhost> <20150721042932.GF23525@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Michal Suchanek Cc: Brian Norris , Marek Vasut , Richard Cochran , Geert Uytterhoeven , Mark Rutland , Krzysztof Kozlowski , Geert Uytterhoeven , MTD Maling List , Alison Chaiken , Bean Huo =?utf-8?B?6ZyN5paM5paMIChiZWFuaHVvKQ==?= , "linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Russell King , =?utf-8?B?UmFmYcWCIE1pxYJlY2tp?= , Kukjin Kim , Ben Hutchings , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Pawel Moll , Ian Campbell , Kumar Gala List-Id: devicetree@vger.kernel.org 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. -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html