Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752738AbaDDMO1 (ORCPT ); Fri, 4 Apr 2014 08:14:27 -0400 Received: from mail-yh0-f45.google.com ([209.85.213.45]:40643 "EHLO mail-yh0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752294AbaDDMOY (ORCPT ); Fri, 4 Apr 2014 08:14:24 -0400 MIME-Version: 1.0 In-Reply-To: <20140404100919.GO14763@sirena.org.uk> References: <1396523431-14519-1-git-send-email-harinik@xilinx.com> <1396523431-14519-2-git-send-email-harinik@xilinx.com> <20140403213446.GB14763@sirena.org.uk> <20140404100919.GO14763@sirena.org.uk> Date: Fri, 4 Apr 2014 17:44:23 +0530 Message-ID: Subject: Re: [PATCH v2 2/2] devicetree: Add devicetree bindings documentation for Cadence SPI From: Harini Katakam To: Mark Brown Cc: Grant Likely , Rob Herring , Pawel Moll , Mark Rutland , "ijc+devicetree@hellion.org.uk" , Kumar Gala , linux-spi@vger.kernel.org, "linux-kernel@vger.kernel.org" , "devicetree@vger.kernel.org" , "linux-doc@vger.kernel.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 Hi Mark, On Fri, Apr 4, 2014 at 3:39 PM, Mark Brown wrote: > On Fri, Apr 04, 2014 at 08:30:38AM +0530, Harini Katakam wrote: >> On Fri, Apr 4, 2014 at 3:04 AM, Mark Brown wrote: >> > On Thu, Apr 03, 2014 at 04:40:31PM +0530, Harini Katakam wrote: > >> >> +Optional properties: >> >> +- num-cs : Number of chip selects used. > >> > How does this translate to the hardware? > >> This IP can drive 4 slaves. >> The CS line to be driven is selected in spi device structure and >> that is driven by the software. > > So why specify this in the binding at all? If the device always has the > same number of chip selects it's redundant. I'm sorry, I should have explained that better. The IP can support upto 4 chip selects. The num-cs value here is the number of chip selects actually used on the board. > >> >> + num-cs = /bits/ 16 <4>; > >> > What's going on with the /bits/ - is this something that's required for >> > the property? > >> The master->num-chipselect property is 16 bit but writing <4> here directly >> leads to 0 being read in of_property_read (because it's big endian). >> Instead using of property read u32 and then copying, we decided to do this. >> This was discussed on v2 between Michal and Rob: > > No, don't do that. You're contorting the binding to serve Linux's > implementation needs and you've not documented this requirement either. > If there *was* a need to have the number be 16 bits you'd need to > document that reqirement in the binding, though like I say I don't think > the number needs to be there at all. OK. I'll remove the /bits/ 16 and handle it in the driver. Regards, Harini -- 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/