From patchwork Mon Jul 6 07:17:53 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marc Kleine-Budde X-Patchwork-Id: 11644997 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id EADD1912 for ; Mon, 6 Jul 2020 07:18:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D338520C09 for ; Mon, 6 Jul 2020 07:18:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728110AbgGFHSI (ORCPT ); Mon, 6 Jul 2020 03:18:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45694 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728192AbgGFHSI (ORCPT ); Mon, 6 Jul 2020 03:18:08 -0400 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 05117C08C5E0 for ; Mon, 6 Jul 2020 00:18:07 -0700 (PDT) Received: from heimdall.vpn.pengutronix.de ([2001:67c:670:205:1d::14] helo=blackshift.org) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1jsLO7-0004BC-8a; Mon, 06 Jul 2020 09:18:03 +0200 From: Marc Kleine-Budde To: Mark Brown Cc: Maxime Ripard , Chen-Yu Tsai , linux-spi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kernel@pengutronix.de, Marc Kleine-Budde Subject: [PATCH 1/9] spi: spi-sun6i: sun6i_spi_transfer_one(): fix setting of clock rate Date: Mon, 6 Jul 2020 09:17:53 +0200 Message-Id: <20200706071801.558394-2-mkl@pengutronix.de> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200706071801.558394-1-mkl@pengutronix.de> References: <20200706071801.558394-1-mkl@pengutronix.de> MIME-Version: 1.0 X-SA-Exim-Connect-IP: 2001:67c:670:205:1d::14 X-SA-Exim-Mail-From: mkl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-spi@vger.kernel.org Sender: linux-spi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-spi@vger.kernel.org A SPI transfer defines the _maximum_ speed of the SPI transfer. However the driver doesn't take into account that the clock divider is always rounded down (due to integer arithmetics). This results in a too high clock rate for the SPI transfer. E.g.: with a mclk_rate of 24 MHz and a SPI transfer speed of 10 MHz, the original code calculates a reg of "0", which results in a effective divider of "2" and a 12 MHz clock for the SPI transfer. This patch fixes the issue by using DIV_ROUND_UP() instead of a plain integer division. While there simplify the divider calculation for the CDR1 case, use order_base_2() instead of two ilog2() calculations. Fixes: 3558fe900e8a ("spi: sunxi: Add Allwinner A31 SPI controller driver") Signed-off-by: Marc Kleine-Budde --- drivers/spi/spi-sun6i.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/drivers/spi/spi-sun6i.c b/drivers/spi/spi-sun6i.c index ecea15534c42..fa11cc0e809b 100644 --- a/drivers/spi/spi-sun6i.c +++ b/drivers/spi/spi-sun6i.c @@ -198,7 +198,7 @@ static int sun6i_spi_transfer_one(struct spi_master *master, struct spi_transfer *tfr) { struct sun6i_spi *sspi = spi_master_get_devdata(master); - unsigned int mclk_rate, div, timeout; + unsigned int mclk_rate, div, div_cdr1, div_cdr2, timeout; unsigned int start, end, tx_time; unsigned int trig_level; unsigned int tx_len = 0; @@ -287,14 +287,12 @@ static int sun6i_spi_transfer_one(struct spi_master *master, * First try CDR2, and if we can't reach the expected * frequency, fall back to CDR1. */ - div = mclk_rate / (2 * tfr->speed_hz); - if (div <= (SUN6I_CLK_CTL_CDR2_MASK + 1)) { - if (div > 0) - div--; - - reg = SUN6I_CLK_CTL_CDR2(div) | SUN6I_CLK_CTL_DRS; + div_cdr1 = DIV_ROUND_UP(mclk_rate, tfr->speed_hz); + div_cdr2 = DIV_ROUND_UP(div_cdr1, 2); + if (div_cdr2 <= (SUN6I_CLK_CTL_CDR2_MASK + 1)) { + reg = SUN6I_CLK_CTL_CDR2(div_cdr2 - 1) | SUN6I_CLK_CTL_DRS; } else { - div = ilog2(mclk_rate) - ilog2(tfr->speed_hz); + div = min(SUN6I_CLK_CTL_CDR1_MASK, order_base_2(div_cdr1)); reg = SUN6I_CLK_CTL_CDR1(div); }