From patchwork Fri Mar 30 10:01:22 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fabrice Gasnier X-Patchwork-Id: 10317543 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 5078B60383 for ; Fri, 30 Mar 2018 10:02:52 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 412AE2A1DD for ; Fri, 30 Mar 2018 10:02:52 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 35BF42A304; Fri, 30 Mar 2018 10:02:52 +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=-1.9 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID 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 C50672A1DD for ; Fri, 30 Mar 2018 10:02:51 +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=BXj29v5FddVLm/71y7U+/yGqH3D2fM3sF3k7RC2+uiw=; b=gFAG8z+419+iU9 MqeSnchAC9k3LqD3BD90FZ0vXi6NDagfvbYjTNcevtr/bTv1BlQO1itaMGvloYPBnu1Td5vv4C8V1 7IyKiefFZ4ztVKJ1Wc12ZSEQUQtyP3zqS9p/GfTzAZ8X0fjPimNSBEX1GcbcFz5BvdtvuumBmzDzc hdpSm3sgpKRUAlvrGUgN5eeuxXPJTmgHPIBvL7avH/59udNPakTxprqx7bJj/TuBiAKgnw1hVAuBX Hy4eYxTCOLbjc2BUKXGAefRKwWp8e4R+yxiB4ldjJHWodnORaVfRsyp/iRBWxGVm45/9gRgBuOP7l kM6DBWD2BDHdo9qDD10Q==; 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 1f1qrn-00052y-7F; Fri, 30 Mar 2018 10:02:39 +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 1f1qri-000507-1o for linux-arm-kernel@lists.infradead.org; Fri, 30 Mar 2018 10:02:36 +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 w2U9xSOX009484; Fri, 30 Mar 2018 12:02:00 +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 2h0vmnp0xw-1 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT); Fri, 30 Mar 2018 12:02:00 +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 1B67131; Fri, 30 Mar 2018 10:02:00 +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 E6D4926B7; Fri, 30 Mar 2018 10:01:59 +0000 (GMT) Received: from localhost (10.75.127.48) by SFHDAG5NODE3.st.com (10.75.127.15) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 30 Mar 2018 12:01:59 +0200 From: Fabrice Gasnier To: , , Subject: [PATCH v3 4/6] pwm: stm32: improve capture by tuning counter prescaler Date: Fri, 30 Mar 2018 12:01:22 +0200 Message-ID: <1522404084-24903-5-git-send-email-fabrice.gasnier@st.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1522404084-24903-1-git-send-email-fabrice.gasnier@st.com> References: <1522404084-24903-1-git-send-email-fabrice.gasnier@st.com> MIME-Version: 1.0 X-Originating-IP: [10.75.127.48] X-ClientProxiedBy: SFHDAG3NODE2.st.com (10.75.127.8) To SFHDAG5NODE3.st.com (10.75.127.15) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2018-03-30_04:, , signatures=0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20180330_030234_404020_217C9DC5 X-CRM114-Status: GOOD ( 15.30 ) 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, 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 00c6251..c6eb0a8 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;