Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1162155AbbKTIpx (ORCPT ); Fri, 20 Nov 2015 03:45:53 -0500 Received: from mail-wm0-f44.google.com ([74.125.82.44]:38809 "EHLO mail-wm0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757554AbbKTIpu (ORCPT ); Fri, 20 Nov 2015 03:45:50 -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> Date: Fri, 20 Nov 2015 09:45:48 +0100 Message-ID: Subject: Re: [linux-sunxi] [PATCH] spi: dts: sun4i: Add support for inter-word wait cycles using the SPI Wait Clock Register From: Marcus Weseloh To: Julian Calaby 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: 1193 Lines: 28 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. Cheers, Marcus -- 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/