Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1162603AbbKTKM2 (ORCPT ); Fri, 20 Nov 2015 05:12:28 -0500 Received: from mail-io0-f182.google.com ([209.85.223.182]:36197 "EHLO mail-io0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751517AbbKTKMY (ORCPT ); Fri, 20 Nov 2015 05:12:24 -0500 MIME-Version: 1.0 In-Reply-To: References: <1447948422-4915-1-git-send-email-mweseloh42@gmail.com> <1447948422-4915-2-git-send-email-mweseloh42@gmail.com> From: Julian Calaby Date: Fri, 20 Nov 2015 21:12:04 +1100 Message-ID: Subject: Re: [linux-sunxi] [PATCH] spi: dts: sun4i: Add support for inter-word wait cycles using the SPI Wait Clock Register To: Marcus Weseloh Cc: linux-sunxi , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Maxime Ripard , Mark Brown , devicetree , "Mailing List, Arm" , "linux-kernel@vger.kernel.org" , linux-spi@vger.kernel.org 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: 1704 Lines: 42 Hi Marcus, On Fri, Nov 20, 2015 at 7:45 PM, Marcus Weseloh wrote: > Hi Julian, > > 2015-11-19 23:59 GMT+01:00 Julian Calaby : >> Should you possibly hide the 3 clock periods from the user? >> >> I.e. they set whatever they want for the wdelay, we set it to the >> closest number we can that's greater or equal to what they ask for. > > That's a good idea and much better than having to remember to subtract > 3 cycles from the desired wait time! > > But it would mean that this magic number becomes part of the driver > code. I have found no official documentation that mentions those > additional cycles. While I have checked many different transmission > speeds using both CDR1 and CDR2 divider configurations, there is still > the possibility that the behaviour changes with weird SPI module > configurations... And I've only tested it on A20 hardware. So it would > be great if somebody else with access to A10 hardware and an > oscilloscope could check if we have a consistent 3 cycle overhead. Having magic numbers is kind-of a drivers' job. (and the wdelay should arguably be a core-spi thing, not a sunxi thing, but that's a separate discussion) If it is different for other SoCs, then you might have to move that constant somewhere else and introduce new compatible strings for them. Thanks, -- Julian Calaby Email: julian.calaby@gmail.com Profile: http://www.google.com/profiles/julian.calaby/ -- 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/