From patchwork Mon Nov 28 16:41:47 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nathan Barrett-Morrison X-Patchwork-Id: 629837 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EF2ABC4332F for ; Mon, 28 Nov 2022 16:44:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230035AbiK1QoT (ORCPT ); Mon, 28 Nov 2022 11:44:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38476 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230208AbiK1QoR (ORCPT ); Mon, 28 Nov 2022 11:44:17 -0500 Received: from mail-qt1-x82c.google.com (mail-qt1-x82c.google.com [IPv6:2607:f8b0:4864:20::82c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A067C1AD94 for ; Mon, 28 Nov 2022 08:44:14 -0800 (PST) Received: by mail-qt1-x82c.google.com with SMTP id l2so7045379qtq.11 for ; Mon, 28 Nov 2022 08:44:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=timesys-com.20210112.gappssmtp.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=XXSSzXQqwpqTp8kvMCywn3wDULboBrcJlaRyokBQ21k=; b=fejHIyNfaphEgkYKnCMhaL2S9tzT4NlOpJKoyQ/v4qpJLWqHeLSj8Q/Bt8hkvQgiNW kf190UpnS4b3+SMrlzWDpyElTt4EXZp6IxFfn6XkfhiwmSmG3dzw0+kBSjHu6elG+sBH 76tF+npGB5JvlV3CaGWJ+G39ZWHYT+hbM37sQOLlOzLG5Uxtt87VXn+BS9DH3YYNPH0P yCzDWDNfhT6rLYKJVvz8pc1exJUAbkb0fmDJO8CDCXipAI+F8UtVaA//tWLZw+FAY62w wsVbyuA4jzpTNb2zMM6z0KtyvzP/DPYa0lmYAzF3y+okU7yq3liWGN9ajF3L8AUB8EqB WoIw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=XXSSzXQqwpqTp8kvMCywn3wDULboBrcJlaRyokBQ21k=; b=T+UWZGkpRk+koTfhyI2B1YLizcROprd9vxdgjszfiiFvibdq0Xc2LpqRKhFVwYbg5O siLbJ/SJAKx2/WqI+TADccQVaTx1V/KxocTyhCYmu57Gmtq/Dd0KhNITYA4axXcqJJ4p kHKbPff+Fw5UpogDN3xe3FtIl3K7DvmMn9ZgSclAJIdbc4C5HA8BNvVxEjKcY8uJo3oA pz9AzbC6JDdFrus/O7jCKGeytcROM1H5MeUfjy+yQ6Ml8eo7wxbBz86X9HkDvQsmveqp ID5P0+yz305EaHzkn+LnV7kvWyFLSRM1iOKiCvUL57+f6hfZdc/DRoskVhiHAD5ZV9cz ++oA== X-Gm-Message-State: ANoB5pkDMLm8G63STRHSkbpT51KHdNvvFf4L0kDTBTTRsZOnz7KrmLa7 xbbTEn+CIJw1HaFg7owL1DaMpw== X-Google-Smtp-Source: AA0mqf7AtxhiM423WOE+xFxDY3JxLwBVPHLaeViLYBR9XRHLigeZ8k+EOCSYlJRNcx4+zIoCpf6HbA== X-Received: by 2002:ac8:604e:0:b0:3a2:9fcd:59c8 with SMTP id k14-20020ac8604e000000b003a29fcd59c8mr34598175qtm.273.1669653853577; Mon, 28 Nov 2022 08:44:13 -0800 (PST) Received: from nathan-ideapad.. (d-75-76-18-234.oh.cpe.breezeline.net. [75.76.18.234]) by smtp.gmail.com with ESMTPSA id bn31-20020a05620a2adf00b006b95b0a714esm8724614qkb.17.2022.11.28.08.44.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Nov 2022 08:44:13 -0800 (PST) From: Nathan Barrett-Morrison Cc: nathan.morrison@timesys.com, greg.malysa@timesys.com, Mark Brown , linux-spi@vger.kernel.org (open list:SPI SUBSYSTEM), linux-kernel@vger.kernel.org (open list) Subject: [PATCH] spi: cadence-quadspi: Add minimum operable clock rate warning to baudrate divisor calculation Date: Mon, 28 Nov 2022 11:41:47 -0500 Message-Id: <20221128164147.158441-1-nathan.morrison@timesys.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 To: unlisted-recipients:; (no To-header on input) Precedence: bulk List-ID: X-Mailing-List: linux-spi@vger.kernel.org This Cadence QSPI IP has a 4-bit clock divisor field for baud rate division. For example: 0b0000 = /2 0b0001 = /4 0b0010 = /6 ... 0b1111 = /32 The maximum divisor is 32 (when div = CQSPI_REG_CONFIG_BAUD_MASK). If we assume a reference clock of 500MHz and we set our spi-max-frequency to something low, such as 10 MHz. The calculated bit field for the divisor ends up being: DIV_ROUND_UP(500000000/(2*10000000))-1 = 25 25 is 0b11001... which truncates to a divisor field of 0b1001 (or /20). This is higher than our anticipated max-frequency of 10MHz (500MHz/20 = 25 MHz). Instead, let's make sure we're always using the maximum divisor (/32) in this case and give the user a warning about the rate adjustment. Signed-off-by: Nathan Barrett-Morrison --- drivers/spi/spi-cadence-quadspi.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c index 447230547945..21b60b354404 100644 --- a/drivers/spi/spi-cadence-quadspi.c +++ b/drivers/spi/spi-cadence-quadspi.c @@ -1119,6 +1119,14 @@ static void cqspi_config_baudrate_div(struct cqspi_st *cqspi) /* Recalculate the baudrate divisor based on QSPI specification. */ div = DIV_ROUND_UP(ref_clk_hz, 2 * cqspi->sclk) - 1; + /* Maximum baud divisor */ + if (div > CQSPI_REG_CONFIG_BAUD_MASK) { + div = CQSPI_REG_CONFIG_BAUD_MASK; + dev_warn(&cqspi->pdev->dev, + "Unable to adjust clock <= %d hz. Reduced to %d hz\n", + cqspi->sclk, ref_clk_hz/((div+1)*2)); + } + reg = readl(reg_base + CQSPI_REG_CONFIG); reg &= ~(CQSPI_REG_CONFIG_BAUD_MASK << CQSPI_REG_CONFIG_BAUD_LSB); reg |= (div & CQSPI_REG_CONFIG_BAUD_MASK) << CQSPI_REG_CONFIG_BAUD_LSB;