From patchwork Mon Nov 15 03:43:29 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Liam Beguin X-Patchwork-Id: 12618657 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4B5E4C433EF for ; Mon, 15 Nov 2021 03:44:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2DE7B60551 for ; Mon, 15 Nov 2021 03:44:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237015AbhKODq7 (ORCPT ); Sun, 14 Nov 2021 22:46:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50818 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236996AbhKODqs (ORCPT ); Sun, 14 Nov 2021 22:46:48 -0500 Received: from mail-qk1-x731.google.com (mail-qk1-x731.google.com [IPv6:2607:f8b0:4864:20::731]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C61A7C06120A; Sun, 14 Nov 2021 19:43:50 -0800 (PST) Received: by mail-qk1-x731.google.com with SMTP id p4so6964673qkm.7; Sun, 14 Nov 2021 19:43:50 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=jbkvNiZPeqKZDFobOFBdHT7ASm74e41udPizXrb8loc=; b=gqQu1qRYyYkbkTxRfa2gJq13cZESiPU6TwYXyhhtszE8OP2w0N/JT842Bqu0t8la7u 9dTURCd3Q8xz+cqeusNg8cgUPy9NrTsdINrJUjf0RwKSg9u7WYr5G/DHaUz7VZTW2LtF qdCsWFfpOdu9KTRoov6p4KQzRDR10ChVZPotvFX6yrGz7jrW9/6sn6WUid5PN6N+sq9S bQ8Ahys8rltIeg5lyX36PwJMXRNysE8+yY/e1pmHniL//RFm81MkettaJHYQLnoJuq9L M8qMXkqJQz08lyQGYr+ajgSnzxV2aqxPi0SeA1Ip7q/rFRlzyCPYUOm6ffgfZhViygoo jlCw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=jbkvNiZPeqKZDFobOFBdHT7ASm74e41udPizXrb8loc=; b=e6cksk26ka196tMSJXeZDp2MwvgD5+osKtRZ+/Bz5NpyjdCPxP+j9I+5grFShahegb rb5rwuO9gI8vc/h/mHXJz3Dwf52TFUpGwXYRLBwfQkeT9Zz0lNffDiRt9Yn8pIiy93GW XRjgEiGkCJ+ozPjWUz+wHcmW0f9VS9kqQuOy/MNCuICo+71IfHU/AefVMf4U3dLY3ED5 +C8tnAY7Fy+1XOBCA95y3FNphnEWP2aOZjQ+quyET+LcT3gcbSXI5jBQycwBispKSg5b /UvOVjQy1DpM+eHLa/+9E8jyqIErhuDQoecYI4ifwfnCb0g0ODcVGvdY+95ycg3z67hE dMQw== X-Gm-Message-State: AOAM532ysMEQoLeIwS9UcOM6l6Yne2rAj6ica+v28h0jvkInd9Qu3E5C NiQFDKspDn+ZuwbE4B3g6swi1m+dJRY= X-Google-Smtp-Source: ABdhPJwXbbMyQTknT3hcPa31IUIno454eah6cdfqQiinZd09ZQjFYtKMbMa3fLmY/o2bEBfNR0awtA== X-Received: by 2002:a05:620a:4248:: with SMTP id w8mr27476306qko.228.1636947829962; Sun, 14 Nov 2021 19:43:49 -0800 (PST) Received: from shaak.. 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[198.48.202.89]) by smtp.gmail.com with ESMTPSA id h5sm206519qkn.62.2021.11.14.19.43.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Nov 2021 19:43:49 -0800 (PST) From: Liam Beguin To: liambeguin@gmail.com, peda@axentia.se, jic23@kernel.org, lars@metafoo.de Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, devicetree@vger.kernel.org, robh+dt@kernel.org Subject: [PATCH v9 09/14] iio: afe: rescale: fix accuracy for small fractional scales Date: Sun, 14 Nov 2021 22:43:29 -0500 Message-Id: <20211115034334.1713050-10-liambeguin@gmail.com> X-Mailer: git-send-email 2.32.0.452.g940fe202adcb In-Reply-To: <20211115034334.1713050-1-liambeguin@gmail.com> References: <20211115034334.1713050-1-liambeguin@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org From: Liam Beguin The approximation caused by integer divisions can be costly on smaller scale values since the decimal part is significant compared to the integer part. Switch to an IIO_VAL_INT_PLUS_NANO scale type in such cases to maintain accuracy. Signed-off-by: Liam Beguin --- drivers/iio/afe/iio-rescale.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c index 17036130d364..8a2f1c0ca5a3 100644 --- a/drivers/iio/afe/iio-rescale.c +++ b/drivers/iio/afe/iio-rescale.c @@ -22,7 +22,7 @@ int rescale_process_scale(struct rescale *rescale, int scale_type, int *val, int *val2) { s64 tmp; - s32 rem; + s32 rem, rem2; u32 mult; u32 neg; @@ -38,9 +38,26 @@ int rescale_process_scale(struct rescale *rescale, int scale_type, tmp = (s64)*val * 1000000000LL; tmp = div_s64(tmp, rescale->denominator); tmp *= rescale->numerator; - tmp = div_s64(tmp, 1000000000LL); + + tmp = div_s64_rem(tmp, 1000000000LL, &rem); *val = tmp; - return scale_type; + + if (!rem) + return scale_type; + + if (scale_type == IIO_VAL_FRACTIONAL) + tmp = *val2; + else + tmp = 1 << *val2; + + rem2 = *val % (int)tmp; + *val = *val / (int)tmp; + + *val2 = rem / (int)tmp; + if (rem2) + *val2 += div_s64((s64)rem2 * 1000000000LL, tmp); + + return IIO_VAL_INT_PLUS_NANO; case IIO_VAL_INT_PLUS_NANO: case IIO_VAL_INT_PLUS_MICRO: if (scale_type == IIO_VAL_INT_PLUS_NANO)