Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754469AbbLTMr5 (ORCPT ); Sun, 20 Dec 2015 07:47:57 -0500 Received: from mail-lf0-f48.google.com ([209.85.215.48]:35447 "EHLO mail-lf0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754424AbbLTMrq (ORCPT ); Sun, 20 Dec 2015 07:47:46 -0500 MIME-Version: 1.0 In-Reply-To: <20151218111627.GM30359@lukather> References: <1450352427-25350-1-git-send-email-mweseloh42@gmail.com> <1450352427-25350-3-git-send-email-mweseloh42@gmail.com> <20151218111627.GM30359@lukather> Date: Sun, 20 Dec 2015 13:47:43 +0100 Message-ID: Subject: Re: [PATCH v5 2/2] spi: sun4i: Add support for wait time between word transmissions From: Marcus Weseloh To: Maxime Ripard Cc: linux-sunxi , Chen-Yu Tsai , devicetree , Ian Campbell , Kumar Gala , "Mailing List, Arm" , linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org, Mark Brown , Mark Rutland , Pawel Moll , Rob Herring 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: 1790 Lines: 46 Hi, 2015-12-18 12:16 GMT+01:00 Maxime Ripard : >> sun4i_spi_write(sspi, SUN4I_CLK_CTL_REG, reg); >> >> + /* >> + * Setup wait time between words. >> + * >> + * Wait time is set in SPI_CLK cycles. The SPI hardware needs 3 >> + * additional cycles to setup the wait counter, so the minimum delay >> + * time is 4 cycles. >> + */ >> + if (spi->word_wait_ns) { >> + clk_ns = DIV_ROUND_UP(1000000000, tfr->speed_hz); > > You should use the actual rate of the clock returned by clk_get_rate > (or probably just use mclk_rate). > > The clock driver might round the frequency to something else than what > was set in clk_set_rate, which would make your calculation here a bit > off. Yes, good point! And as the wait clock counter is based on the actual SPI_CLK and not the mod clock, I need to calculate the exact clock myself before handling the wait clock setting. Will amend the patch and send a new version. While looking into this, I also noticed a problem with a previous patch of mine, which changed the spi-sun[46]i to use transfer->speed_hz instead of the spi->max_speed_hz: I also changed the mclk_rate calculation to be based on tfr->speed_hz, which should have stayed with spi->max_speed_hz. In the current state, the clock calculations only ever increase mclk_rate, wich leads to very different clocks being set depending on which clock was used on the previous transfer. Will send a fix for that as well in a separate patch. 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/