From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B12A1C433E0 for ; Wed, 30 Dec 2020 16:21:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7E32B20786 for ; Wed, 30 Dec 2020 16:21:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726533AbgL3QV0 (ORCPT ); Wed, 30 Dec 2020 11:21:26 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726323AbgL3QVZ (ORCPT ); Wed, 30 Dec 2020 11:21:25 -0500 Received: from mail-ot1-x330.google.com (mail-ot1-x330.google.com [IPv6:2607:f8b0:4864:20::330]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 220D6C06179C; Wed, 30 Dec 2020 08:20:45 -0800 (PST) Received: by mail-ot1-x330.google.com with SMTP id q25so15738345otn.10; Wed, 30 Dec 2020 08:20:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=kaKOMj3HUFKT00qKqs+P+UOKiqeyEkDl/aHWHZhY7t0=; b=P56V8HJtMvKUJCE7c4G/vUM4joj1rNZGM7xQpU9G/KzkxEd0g28EYZ6xNAYy2c5OSn TmLe+dOhvZTYus1KhDrlqHs7lq8XijY4rA1/ENNgHkaD5bmWx3TJKlni0ffjmVpAlYM5 XEBGMPUGpzuIYRdkCa5IEIQQRiUZYNvQkNm4wZO0n3aqoC+40PDwowZAktu6yHb9AXr6 LfnUIWT83Yy3SK7JMxbvLy5kzwimiugW5+LQx9THgPCQSndFb645CEuG9yBePgSdQAF0 /H7tdYHRB7j8d06WfwKNvR2W6NDI3G524gPV7qRK5ZSsBF37ahVwEBD5sKCZC9gsdJsX AQUQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition :content-transfer-encoding:in-reply-to:user-agent; bh=kaKOMj3HUFKT00qKqs+P+UOKiqeyEkDl/aHWHZhY7t0=; b=STzb0Xu3/h3Fxbv+hjdibZunkPlRkdQpxfH8YLtvidygN9ru9fgWe+NUAW74qn/f0E py+B6GH+8/nRYVI28uXjbLBpc5ijE+LuPe05yKryfmhvhDaZJWnvE8kZ1ZJ7dik19Haf Sq0hN0um2RiXNIPh0HyEw+42wN371oF92flMHmi+zl2lk0MXuSGZioNlqz+7XHZdbRhx f9AvngAJJ4davI5Nl+TjyDmubFrpTjhKucIIx0z85wJWBEYWdtGAIpJK3/ikR+p3QKAg HFafjps9tDxwZofII565ejeWKkLoiJ3hK1byKVLobCk6lvvgflf1o0HEiBq0MVaUgzci dVdg== X-Gm-Message-State: AOAM5315hWFRgP1oMgjt8TZMtLu6EYJNYxCDJbaFnybydzgyKwDscEbv BmUkH0/nlInMrTiJc8itDYw= X-Google-Smtp-Source: ABdhPJxyayBJ3Ss4JlHGrgdlSnVn2JlrP6FqN3anUH1T0ISTq0I/C7kyu1noSzKa5xL9BsiaOd5P8g== X-Received: by 2002:a9d:a61:: with SMTP id 88mr37736451otg.18.1609345244597; Wed, 30 Dec 2020 08:20:44 -0800 (PST) Received: from localhost ([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id x1sm6295812ota.32.2020.12.30.08.20.43 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Wed, 30 Dec 2020 08:20:43 -0800 (PST) Sender: Guenter Roeck Date: Wed, 30 Dec 2020 08:20:42 -0800 From: Guenter Roeck To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Cc: Bartlomiej Zolnierkiewicz , Jean Delvare , Thierry Reding , Lee Jones , linux-hwmon@vger.kernel.org, linux-pwm@vger.kernel.org, kernel@pengutronix.de Subject: Re: [PATCH 1/2] hwmon: pwm-fan: Ensure that calculation doesn't discard big period values Message-ID: <20201230162042.GA102327@roeck-us.net> References: <20201215092031.152243-1-u.kleine-koenig@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20201215092031.152243-1-u.kleine-koenig@pengutronix.de> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org On Tue, Dec 15, 2020 at 10:20:30AM +0100, Uwe Kleine-König wrote: > With MAX_PWM being defined to 255 the code > > unsigned long period; > ... > period = ctx->pwm->args.period; > state.duty_cycle = DIV_ROUND_UP(pwm * (period - 1), MAX_PWM); > > calculates a too small value for duty_cycle if the configured period is > big (either by discarding the 64 bit value ctx->pwm->args.period or by > overflowing the multiplication). As this results in a too slow fan and > so maybe an overheating machine better be safe than sorry and error out > in .probe. > > Signed-off-by: Uwe Kleine-König Applied. Thanks, Guenter > --- > drivers/hwmon/pwm-fan.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > > base-commit: 2c85ebc57b3e1817b6ce1a6b703928e113a90442 > > diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c > index 1f63807c0399..ec171f2b684a 100644 > --- a/drivers/hwmon/pwm-fan.c > +++ b/drivers/hwmon/pwm-fan.c > @@ -324,8 +324,18 @@ static int pwm_fan_probe(struct platform_device *pdev) > > ctx->pwm_value = MAX_PWM; > > - /* Set duty cycle to maximum allowed and enable PWM output */ > pwm_init_state(ctx->pwm, &state); > + /* > + * __set_pwm assumes that MAX_PWM * (period - 1) fits into an unsigned > + * long. Check this here to prevent the fan running at a too low > + * frequency. > + */ > + if (state.period > ULONG_MAX / MAX_PWM + 1) { > + dev_err(dev, "Configured period too big\n"); > + return -EINVAL; > + } > + > + /* Set duty cycle to maximum allowed and enable PWM output */ > state.duty_cycle = ctx->pwm->args.period - 1; > state.enabled = true; >