From patchwork Tue Jan 16 12:43:49 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fabrice Gasnier X-Patchwork-Id: 10166751 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 3B67B601E7 for ; Tue, 16 Jan 2018 12:45:24 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 2B15D28449 for ; Tue, 16 Jan 2018 12:45:24 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1EDA128520; Tue, 16 Jan 2018 12:45:24 +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 1F8F328449 for ; Tue, 16 Jan 2018 12:45:23 +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=3HJ+i34/r0rAtsmuJyK0Y/IpeS82hmSxA0joMxu/7Y4=; b=fp6iUXo5xodMSv ulNL0EiyHo2F7qoDZS02ASJachplvTMS/2+nMq8xqPzAist7SvFqLOp7/OSBG5bj6t4BxXFeqHVmu wFz5CyLTqRHW3cbl99ZnZ1Jvtbvm4i5QnQ455xkafPiVJw8ktFBGQ6H/BeMvYJAFsVxpJ2G7xtzPD 7ORGD6xRxWJ45+H+A3qaJpSG9b9FZgqNJkgHmVyRUt8ALKIh/xTnQmCRlONCSapVPoOZ/K6L6jEmw jfTIYLD4RRStoQ0O8tsbQAy4ULSQC0OgexW+7jUj64KAZUu8KfOzz8Qzq8pbCbDAup+ViFuPxJAcN +y4Oc9K2WQD4Lxghsmug==; 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 1ebQcD-0006SE-JA; Tue, 16 Jan 2018 12:45:21 +0000 Received: from mx08-00178001.pphosted.com ([91.207.212.93] helo=mx07-00178001.pphosted.com) by bombadil.infradead.org with esmtps (Exim 4.89 #1 (Red Hat Linux)) id 1ebQc9-0005QQ-Mk for linux-arm-kernel@lists.infradead.org; Tue, 16 Jan 2018 12:45:19 +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 w0GChhx7017697; Tue, 16 Jan 2018 13:44:44 +0100 Received: from beta.dmz-eu.st.com (beta.dmz-eu.st.com [164.129.1.35]) by mx08-00178001.pphosted.com with ESMTP id 2fgye1wr0c-1 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT); Tue, 16 Jan 2018 13:44:44 +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 0A47D3F; Tue, 16 Jan 2018 12:44:44 +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 DBADD26F0; Tue, 16 Jan 2018 12:44:43 +0000 (GMT) Received: from localhost (10.75.127.45) by SFHDAG5NODE3.st.com (10.75.127.15) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Tue, 16 Jan 2018 13:44:43 +0100 From: Fabrice Gasnier To: , , , , Subject: [PATCH 6/8] pwm: stm32: improve capture by tuning counter prescaler Date: Tue, 16 Jan 2018 13:43:49 +0100 Message-ID: <1516106631-18722-7-git-send-email-fabrice.gasnier@st.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1516106631-18722-1-git-send-email-fabrice.gasnier@st.com> References: <1516106631-18722-1-git-send-email-fabrice.gasnier@st.com> MIME-Version: 1.0 X-Originating-IP: [10.75.127.45] X-ClientProxiedBy: SFHDAG5NODE3.st.com (10.75.127.15) To SFHDAG5NODE3.st.com (10.75.127.15) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2018-01-16_05:, , signatures=0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20180116_044518_052616_39736C3D X-CRM114-Status: GOOD ( 12.29 ) 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 --- drivers/pwm/pwm-stm32.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c index b9c7e878..c890404 100644 --- a/drivers/pwm/pwm-stm32.c +++ b/drivers/pwm/pwm-stm32.c @@ -257,7 +257,7 @@ 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; @@ -311,6 +311,30 @@ static int stm32_pwm_capture(struct pwm_chip *chip, struct pwm_device *pwm, raw_prd = priv->capture[0]; raw_dty = priv->capture[1]; + /* + * 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 */ + regmap_write(priv->regmap, TIM_PSC, psc / scale); + ret = stm32_pwm_do_capture(priv, pwm, tmo_ms); + if (ret) + goto stop; + + psc /= scale; + raw_prd = priv->capture[0]; + raw_dty = priv->capture[1]; + } + 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;