From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.221.43 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792670046; b=CNi16pciOo3YL0dN3m75fQFnMKsLuGeyYQyb1rRYKSKtWE8qc770sL+dOwsVCprAZvO2 EN3WQM/S6ZO8uV25MnZNdTDYOYtUAcIvy8SltnMC3cvdzcs16U66Mpy6RB7x83Da4CreD cRVQZefJpVB9jezZJWVQsbfaiZ9mMAmV4dC5YvR9iIkol9dYNkVbxp7WZtgqS6vDzZI+2 AQJASuUoUfmOuqP4gP3tXqa8356w2SVFycsdN8BNuTZUqbBjIwtRJQUOTP/DBv0YxpZr4 9C2LIev4jemplA4Rxumd+x61pVJEgmiM7BLTqecin/OMrPkF72+Z4pelDmZcvvzJItw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792670046; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: From:Date:Subject:MIME-Version:Content-Type:Content-Transfer-Encoding: Message-Id:References:In-Reply-To:To:Cc:X-Mailer; bh=peR+wtMRuf/Lbf3aBVnZb+FceQ6m+uCwk67vJ8kOWzU=; b=CQiYHhooBdSBlo2Z0+YINoUMvXw2CrJ8kvJ8uzHYl6v2ilP7KjqLyvuTR42bBOlFFgI2 lteRG4kZ7XFBQ2wCOGIksh0eV4qd8AJt3IVeBK1aJtbdpOLQL7f1IdV3U2D2MRcJ3d76E YPvR70B0Z8uHA/nq4ZDlc1A5BLRs40Qy7ukOc9idGx1arZwhrgCz1UJz83R0Qe0mF/5sH 7PrtSpcxW745y6NWp4hcs7aGtVUSZKaXC0Ft5L9Quhe9GxXWwnocRPh83Vu0JjLFJu6ug UgEaRleUq7QjRdB1XZBTdrD9ulbfK9HjKiyKr37UHjYuajKu0jEyufmMMngc5r+AvMw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20251104 header.b=oRTKVgbx; arc=none smtp.remote-ip=209.85.221.43 Received: from mail-wr1-f43.google.com (mail-wr1-f43.google.com [209.85.221.43]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 35E5060A2601 for ; Thu, 22 Oct 2026 11:54:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 35E5060A2601 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20251104 header.b=oRTKVgbx Received: by mail-wr1-f43.google.com with SMTP id ffacd0b85a97d-48e1d0e5dafso591565f8f.1 for ; Thu, 22 Oct 2026 04:54:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1792670045; x=1793274845; darn=vger.kernel.org; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :content-type:mime-version:subject:date:from:from:to:cc:subject:date :message-id:reply-to:content-type; bh=peR+wtMRuf/Lbf3aBVnZb+FceQ6m+uCwk67vJ8kOWzU=; b=oRTKVgbxyBlIREX7nZMYP+04H0N8obAoqRFnsZsoK0olwGVDPe8k4ZtzBK+MY80drs TlZFP5ymKxgbUX2oCBuKze2R6SYmG0s7In9DeKQ54P2lAVdmka4SCB+fyFSfRJ9IcNw5 m6QQVw0Nzeb5KocUfYHaue9nRZynhDxOBMkbUFx1+83G2M9uX4MVnQ5RTLy812IW1U89 hVcXSyqz+UjgBLhhYlhl15g3DmMF8XlA2huFyKfdDFey0bGCB2DGjyhQAJqFdtVJoXBz JVUOEMX1VZjDIq2+QYHv6j9BAx2Yre4LDjYYNSJKYK/M0Wbb/jTLjCqXnAAo6OiWjlYU lGkA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1792670045; x=1793274845; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :content-type:mime-version:subject:date:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=peR+wtMRuf/Lbf3aBVnZb+FceQ6m+uCwk67vJ8kOWzU=; b=ojRMZ8N6yBM7l8ucMCbhoWoy14oiXMJXZ5MRaSlIHgvSdJVFoGi9YlIQQ9evWOtK1R xWuu0zNcHHRVEsgEjHXVIWQqrQ/XguXJjeSMqvr+QNVx41KdF3yHUQj3dJsegq13+eoz BK7/57pM1Na1WCL4PwdO+C8aGO1TrSQ8XKFIhEVOTv+fDh47wic/has4JTRlzNqkgPaR M25fsP+Q96AUa7WCL6L42ojqzCc4uy+YRcMCGcmpS6HtO/ognjW/PPeL5o53HLkd5eMd 5MbiGCuGxds7B4XZRoHVfNDV2+31ldIJz47ptc5Melg7Ra2dwH3VELgcak+1eSC+SOlx 5w2A== X-Forwarded-Encrypted: i=1; AKwUvBzNnrSjFpkUgMDMdnFBmtZraDgb2M+9aHDLOmyN2026yruhSq8p4UE+W/Y2+cvu+CcjVZUs5Whxrk/4V8U=@vger.kernel.org X-Gm-Message-State: AFq9FYJGrLm3mFjOrkxhnOd056vDhNuE2amV7frDQCdAU0cJLamTIGnw LeSvWtjsYsbkGQI04MNhaJ6ReMERr2ymD9x585YWpfSYfivT8HAlwisObAzIP21BA7I= X-Gm-Gg: AYBFou1AvUQSnUrQI+/8XVpuQRASOr6n+D4tl7/pS3Hk7gFH4itJD/NN4GBv87k9GtT IQdWTX5GY8gm5bzDLNTz5oAUY0UyamPccRwcOF+BMZeTn3CVJFP2tQsp5CW9J7W1aG57r7D3Gk2 VTWkjdyvsxmzFX0B7h0eeekXrgWWqAm12Eb42IAtt0TGLpJR0H6BRuHoFjdEq6aJHT6+k+vL1Is uzajruJdQihSdm+dooIvFce1JRRVi3OifBCdIR1/0Av8+xHPcC7zunzCZ5gBzVFxb0iot+aJr17 s9/jgRvEijOOjsoaVEmsMVltXstA7ikrySn6FdgXCshQlNyYWKAcv/ZfNDGJi9NyXpdAJ2omzNr 5eSiyBFLTT3EWWH82ZyXFik9ZLIw6aPn9h6wE7xBHRAGxUAZ1gPLUELzYGV89e9QS8bICzUTz4O ETlWNo5lQt4bpN1Pr/dWJMpFqtYukGX1tuVIqy8R3QMh6zHz3bIva95KqLWtYJAckj62fTgwZWE nZLe5RAWJLkLMMeD9eIhSbm5d10nszzOKzx3GFGi/hxaOsDFtCNbkDHUAOS5AdJeEq2rHAvqgom xbWsilwOsQ== X-Received: by 2002:a05:6000:2f8a:b0:48d:f160:efad with SMTP id ffacd0b85a97d-48e2d27f5ffmr5035811f8f.30.1792670044596; Thu, 22 Oct 2026 04:54:04 -0700 (PDT) Received: from localhost (ip-94-113-240-150.net.vodafone.cz. [94.113.240.150]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e25841fe4sm12371400f8f.53.2026.10.22.04.54.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Oct 2026 04:54:04 -0700 (PDT) From: Jan Remes Date: Thu, 22 Oct 2026 13:54:00 +0200 Subject: [PATCH v3 4/4] iio: light: tsl2591: improve lux calculation precision X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261022-first-patch-v3-4-b792e89a429a@mycroftmind.com> References: <20261022-first-patch-v3-0-b792e89a429a@mycroftmind.com> In-Reply-To: <20261022-first-patch-v3-0-b792e89a429a@mycroftmind.com> To: Jonathan Cameron , David Lechner , =?utf-8?q?Nuno_S=C3=A1?= , Andy Shevchenko , Joe Sandom Cc: linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, Jan Remes , Jonathan Cameron , Andy Shevchenko X-Mailer: b4 0.16.0 From: Jan Remes The lux calculation computes the ratio CH1 / CH0 as a truncated integer (CH1 * 1000 / CH0) before using it. When CH1 is close to CH0, the truncation makes the result off by up to ~35%, e.g. CH0 = 56097, CH1 = 55973 at LOW gain and 100ms gives 1.517 lux instead of 1.118 lux. The formula (CH0 - CH1) * (1 - CH1 / CH0) / CPL is equal to (CH0 - CH1)^2 * DF / (CH0 * ATIME_ms * AGAIN) which needs no intermediate ratio. Compute it like that, with a single division at the end. Also report the result in micro-lux instead of milli-lux. At MAX gain and 600ms one count is well below 1 mlx, so the milli-lux resolution throws away information. The numerator still fits into u64. Assisted-by: LLM Reviewed-by: Andy Shevchenko Signed-off-by: Jan Remes --- drivers/iio/light/tsl2591.c | 27 ++++++++++++--------------- 1 file changed, 12 insertions(+), 15 deletions(-) diff --git a/drivers/iio/light/tsl2591.c b/drivers/iio/light/tsl2591.c index e3092ae77a11..fce8cea08201 100644 --- a/drivers/iio/light/tsl2591.c +++ b/drivers/iio/light/tsl2591.c @@ -21,6 +21,7 @@ #include #include #include +#include #include @@ -362,12 +363,12 @@ static int tsl2591_wait_adc_complete(struct tsl2591_chip *chip) * Counts Per Lux (CPL) = (ATIME_ms * AGAIN) / LUX DF * lux = ((C0DATA - C1DATA) * (1 - (C1DATA / C0DATA))) / CPL * - * Scale values to get more representative value of lux i.e. - * lux = ((C0DATA - C1DATA) * (1000 - ((C1DATA * 1000) / C0DATA))) / CPL + * Since (C0DATA - C1DATA) * (1 - (C1DATA / C0DATA)) equals + * (C0DATA - C1DATA)^2 / C0DATA, this is computed in micro-lux as + * lux = ((C0DATA - C1DATA)^2 * LUX DF * 10^6) / (C0DATA * ATIME_ms * AGAIN) * * CPL is not computed on its own: at 1x gain it is below 1 for integration - * times under 500 ms, so the division by LUX DF is folded into the final - * division instead. + * times under 500 ms, so all divisions are done at the end. * * Channel 0 = IR + Visible * Channel 1 = IR only @@ -382,8 +383,8 @@ static int tsl2591_read_channel_data(struct iio_dev *indio_dev, u8 als_data[TSL2591_NUM_DATA_REGISTERS]; int int_time_fval, gain_multi; u16 als_ch0, als_ch1, als_max; + u32 diff, rem; u64 lux; - u32 rem; int ret; ret = tsl2591_wait_adc_complete(chip); @@ -436,19 +437,15 @@ static int tsl2591_read_channel_data(struct iio_dev *indio_dev, int_time_fval = TSL2591_FVAL_TO_MSEC(settings->als_int_time); - /* Calculate lux value */ - lux = (u64)(als_ch0 - als_ch1) * - (1000 - ((als_ch1 * 1000) / als_ch0)) * - TSL2591_LUX_COEFFICIENT; - lux = div_u64(lux, int_time_fval * gain_multi); + /* Calculate lux value in micro-lux */ + diff = als_ch0 - als_ch1; + lux = (u64)diff * diff * TSL2591_LUX_COEFFICIENT * MICRO; + lux = div64_u64(lux, (u64)als_ch0 * int_time_fval * gain_multi); dev_dbg(&client->dev, "Raw lux calculation: %llu\n", lux); - /* Divide by 1000 to get real lux value before scaling */ - *val = div_u64_rem(lux, 1000, &rem); - - /* Get the decimal part of lux reading */ - *val2 = rem * 1000; + *val = div_u64_rem(lux, MICRO, &rem); + *val2 = rem; break; default: -- 2.53.0