From patchwork Fri Jan 26 15:11:37 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fabrice Gasnier X-Patchwork-Id: 10186243 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id CDFE0602C8 for ; Fri, 26 Jan 2018 15:13:13 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id BE0FA29797 for ; Fri, 26 Jan 2018 15:13:13 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id AFEFC29CA4; Fri, 26 Jan 2018 15:13:13 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [65.50.211.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id D0E5A29AB5 for ; Fri, 26 Jan 2018 15:13:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Date:Subject:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=s97ufbAeTrHTW6GXBiePGSZzC/+KlHvQRvePZN21IS0=; b=qwe8rHs7Y5kcbR UAT7J9xpl0JjmW+wsZolYJ5x4C8CU+yIimYBYjzeBWRUUup7ExJYYUFM9iCxNnlLpns1xn+HQf5YJ hR83jOOejHsf5Z3fbUY6KnvQ5vzudR0Xtg9FWFO1iNxTtvYbXzkEN+o3Jc5qnbrMjaGLxYjfQKZ0f GFFKCK1Sd+vABtrYywVtDDqBkJcC8MJryzcilmExAOGefnl+xoOMVvmktlXXYtxTtl7NefVVYjwur qZ8kPHCIoCTyqTkLgIYHiRWbAV4n40asm4+XHf0RCCs2nKR5974PcFj4jTi7QfQAvngKd4J7MLq+f urD9aj4oInDqEmzsxvbQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.89 #1 (Red Hat Linux)) id 1ef5gj-0004fg-Gm; Fri, 26 Jan 2018 15:13:09 +0000 Received: from mx07-00178001.pphosted.com ([62.209.51.94]) by bombadil.infradead.org with esmtps (Exim 4.89 #1 (Red Hat Linux)) id 1ef5gC-00048I-UU for linux-arm-kernel@lists.infradead.org; Fri, 26 Jan 2018 15:12:40 +0000 Received: from pps.filterd (m0046668.ppops.net [127.0.0.1]) by mx07-.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id w0QF3e7O017635; Fri, 26 Jan 2018 16:11:58 +0100 Received: from beta.dmz-eu.st.com (beta.dmz-eu.st.com [164.129.1.35]) by mx07-00178001.pphosted.com with ESMTP id 2fq4fyh7ss-1 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT); Fri, 26 Jan 2018 16:11:58 +0100 Received: from zeta.dmz-eu.st.com (zeta.dmz-eu.st.com [164.129.230.9]) by beta.dmz-eu.st.com (STMicroelectronics) with ESMTP id BA93D3A; Fri, 26 Jan 2018 15:11:57 +0000 (GMT) Received: from Webmail-eu.st.com (sfhdag5node3.st.com [10.75.127.15]) by zeta.dmz-eu.st.com (STMicroelectronics) with ESMTP id 9C5572CE3; Fri, 26 Jan 2018 15:11:57 +0000 (GMT) Received: from localhost (10.75.127.51) by SFHDAG5NODE3.st.com (10.75.127.15) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 26 Jan 2018 16:11:57 +0100 From: Fabrice Gasnier To: , , , , Subject: [PATCH v2 6/8] pwm: stm32: improve capture by tuning counter prescaler Date: Fri, 26 Jan 2018 16:11:37 +0100 Message-ID: <1516979499-3665-7-git-send-email-fabrice.gasnier@st.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1516979499-3665-1-git-send-email-fabrice.gasnier@st.com> References: <1516979499-3665-1-git-send-email-fabrice.gasnier@st.com> MIME-Version: 1.0 X-Originating-IP: [10.75.127.51] X-ClientProxiedBy: SFHDAG6NODE3.st.com (10.75.127.18) To SFHDAG5NODE3.st.com (10.75.127.15) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2018-01-26_08:, , signatures=0 X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, devicetree@vger.kernel.org, benjamin.gaignard@st.com, linux-pwm@vger.kernel.org, linux@armlinux.org.uk, linux-kernel@vger.kernel.org, mcoquelin.stm32@gmail.com, fabrice.gasnier@st.com, linux-arm-kernel@lists.infradead.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP Currently, capture is based on timeout window to configure prescaler. PWM capture framework provides 1s window at the time of writing. There's place for improvement, after input signal has been captured once: - Finer tune counter clock prescaler, by using 1st capture result (with arbitrary margin). - Do a 2nd capture, with scaled capture window. This increases accuracy, especially at high rates. Signed-off-by: Fabrice Gasnier --- Changes in v2: - Adopt DMA read from MFD core. --- drivers/pwm/pwm-stm32.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c index f3a92fc..5dfb296 100644 --- a/drivers/pwm/pwm-stm32.c +++ b/drivers/pwm/pwm-stm32.c @@ -169,7 +169,7 @@ static int stm32_pwm_capture(struct pwm_chip *chip, struct pwm_device *pwm, struct stm32_pwm *priv = to_stm32_pwm_dev(chip); unsigned long long prd, div, dty; unsigned long rate; - unsigned int psc = 0; + unsigned int psc = 0, scale; u32 raw_prd, raw_dty; int ret = 0; @@ -220,6 +220,28 @@ static int stm32_pwm_capture(struct pwm_chip *chip, struct pwm_device *pwm, if (ret) goto stop; + /* + * Got a capture. Try to improve accuracy at high rates: + * - decrease counter clock prescaler, scale up to max rate. + */ + if (raw_prd) { + u32 max_arr = priv->max_arr - 0x1000; /* arbitrary margin */ + + scale = max_arr / min(max_arr, raw_prd); + } else { + scale = priv->max_arr; /* bellow resolution, use max scale */ + } + + if (psc && scale > 1) { + /* 2nd measure with new scale */ + psc /= scale; + regmap_write(priv->regmap, TIM_PSC, psc); + ret = stm32_pwm_raw_capture(priv, pwm, tmo_ms, &raw_prd, + &raw_dty); + if (ret) + goto stop; + } + prd = (unsigned long long)raw_prd * (psc + 1) * NSEC_PER_SEC; result->period = DIV_ROUND_UP_ULL(prd, rate); dty = (unsigned long long)raw_dty * (psc + 1) * NSEC_PER_SEC;