From patchwork Tue Apr 17 13:38:31 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fabrice Gasnier X-Patchwork-Id: 10345085 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 76E7060542 for ; Tue, 17 Apr 2018 13:43:14 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6012E26CFC for ; Tue, 17 Apr 2018 13:43:14 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 5412426D08; Tue, 17 Apr 2018 13:43:14 +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 C88D026CFC for ; Tue, 17 Apr 2018 13:43:13 +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=Pn9v3haHonsAPp L6SJR1dvaj9JhARBY3bZ9fvJeNkrdwdpMHy9bm/auE/cedeeXrgSYrKbGEJPnWEC2af6Nr15E2iMy 2EDLDXMfw9NI8sdhkhHw3QhwnUQ7LjfScp/KnmWNnYWmTi2genvctNy5nP9mwJ5htmVv62+H47g9A Qi0M1Dhp6qf54fRTc9r33sFC6jtYeRWJXNXlMe91cyCZpuo9fT+sw8oS0RvWmRhAmzQ9qof+S9PnO w3ieD+5jo+ZNNoipURmHg0VfL6n1gmbL9qUA482DnGFQXVHNWiUhneGiEEwnT59ndpRX6oCZVurAW jxdW8IBOVz0UyKS+JbvQ==; 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 1f8Qt1-0003ya-OZ; Tue, 17 Apr 2018 13:43:07 +0000 Received: from mx07-00178001.pphosted.com ([62.209.51.94]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1f8QpZ-0000U8-Gp for linux-arm-kernel@lists.infradead.org; Tue, 17 Apr 2018 13:39:37 +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 w3HDcpwE021177; Tue, 17 Apr 2018 15:39:05 +0200 Received: from beta.dmz-eu.st.com (beta.dmz-eu.st.com [164.129.1.35]) by mx07-00178001.pphosted.com with ESMTP id 2hbd6cy2uv-1 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT); Tue, 17 Apr 2018 15:39:05 +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 DE4A241; Tue, 17 Apr 2018 13:39:03 +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 BC8824ECE; Tue, 17 Apr 2018 13:39:03 +0000 (GMT) Received: from localhost (10.75.127.121) by GPXDAG5NODE6.st.com (10.75.127.79) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Tue, 17 Apr 2018 15:39:03 +0200 From: Fabrice Gasnier To: , Subject: [PATCH v5 4/6] pwm: stm32: improve capture by tuning counter prescaler Date: Tue, 17 Apr 2018 15:38:31 +0200 Message-ID: <1523972313-28765-5-git-send-email-fabrice.gasnier@st.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1523972313-28765-1-git-send-email-fabrice.gasnier@st.com> References: <1523972313-28765-1-git-send-email-fabrice.gasnier@st.com> MIME-Version: 1.0 X-Originating-IP: [10.75.127.121] X-ClientProxiedBy: GPXDAG4NODE6.st.com (10.75.127.76) To GPXDAG5NODE6.st.com (10.75.127.79) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2018-04-17_07:, , signatures=0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20180417_063933_891053_1911DC1F X-CRM114-Status: GOOD ( 15.34 ) 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, mcoquelin.stm32@gmail.com, linux-pwm@vger.kernel.org, linux@armlinux.org.uk, linux-kernel@vger.kernel.org, robh+dt@kernel.org, thierry.reding@gmail.com, linux-arm-kernel@lists.infradead.org, benjamin.gaignard@linaro.org, fabrice.gasnier@st.com, dan.carpenter@oracle.com, 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;