From patchwork Mon Apr 16 16:19:19 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fabrice Gasnier X-Patchwork-Id: 10343435 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 1502060542 for ; Mon, 16 Apr 2018 16:21:42 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 04746286EC for ; Mon, 16 Apr 2018 16:21:42 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id ECE0F287E7; Mon, 16 Apr 2018 16:21:41 +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=-2.9 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI autolearn=unavailable version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 69B30286EC for ; Mon, 16 Apr 2018 16:21:41 +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=43G/t/4KBPv3zadWLz+qgzMF+McD/zxEPkzXBkar2Wc=; b=mOGRPTvo2ibxuP rsRn3d1iHq8z95vnjAaIJXgfKYwiGHw7kshgU1XvTHZEQfMAoATCKzfqbVQfOPMp2wLrA/tKq9Xp6 xVorhg6hdCUJ7MAzwS/8268XpCHlNUzruAZ2Yz7Uc3Ltsdrahu7uOaDXlhEhftHjWibRr5ujnL7UI mJrwS3HJwuuylIBrHo+2Yy9c3llxdWeQQzFNkykvxxwvoub4UG5q8NJ4x9DYZZ1yAMBEZInPBEsA6 7NWK7Zj0BFXVOcE2CCspdkyqxIlcOqtXfIamPwSZF1Dx8111uRtYgJXXVtDBcwgdM8nvMeBK3BfOX MGpr84ffdOgSzUQmaO+g==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1f86si-0001UB-SM; Mon, 16 Apr 2018 16:21:28 +0000 Received: from mx08-00178001.pphosted.com ([91.207.212.93] helo=mx07-00178001.pphosted.com) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1f86rM-0007y1-US for linux-arm-kernel@lists.infradead.org; Mon, 16 Apr 2018 16:20:11 +0000 Received: from pps.filterd (m0046660.ppops.net [127.0.0.1]) by mx08-.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id w3GGEaK0004474; Mon, 16 Apr 2018 18:19:36 +0200 Received: from beta.dmz-eu.st.com (beta.dmz-eu.st.com [164.129.1.35]) by mx08-00178001.pphosted.com with ESMTP id 2hb6s6bwfn-1 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT); Mon, 16 Apr 2018 18:19:36 +0200 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 5ABC138; Mon, 16 Apr 2018 16:19:36 +0000 (GMT) Received: from Webmail-eu.st.com (gpxdag5node6.st.com [10.75.127.79]) by zeta.dmz-eu.st.com (STMicroelectronics) with ESMTP id 036CA5149; Mon, 16 Apr 2018 16:19:36 +0000 (GMT) Received: from localhost (10.75.127.118) by GPXDAG5NODE6.st.com (10.75.127.79) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Mon, 16 Apr 2018 18:19:35 +0200 From: Fabrice Gasnier To: , Subject: [PATCH v4 4/6] pwm: stm32: improve capture by tuning counter prescaler Date: Mon, 16 Apr 2018 18:19:19 +0200 Message-ID: <1523895561-4073-5-git-send-email-fabrice.gasnier@st.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1523895561-4073-1-git-send-email-fabrice.gasnier@st.com> References: <1523895561-4073-1-git-send-email-fabrice.gasnier@st.com> MIME-Version: 1.0 X-Originating-IP: [10.75.127.118] X-ClientProxiedBy: GPXDAG1NODE6.st.com (10.75.127.67) To GPXDAG5NODE6.st.com (10.75.127.79) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2018-04-16_08:, , signatures=0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20180416_092005_332875_A7E72769 X-CRM114-Status: GOOD ( 15.28 ) 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@linaro.org, linux-pwm@vger.kernel.org, linux@armlinux.org.uk, linux-kernel@vger.kernel.org, robh+dt@kernel.org, thierry.reding@gmail.com, mcoquelin.stm32@gmail.com, fabrice.gasnier@st.com, linux-arm-kernel@lists.infradead.org, benjamin.gaignard@st.com 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 Reviewed-by: Benjamin Gaignard Acked-by: Thierry Reding --- 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 ed3961b..9a50acd 100644 --- a/drivers/pwm/pwm-stm32.c +++ b/drivers/pwm/pwm-stm32.c @@ -168,7 +168,7 @@ 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; @@ -219,6 +219,28 @@ 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;