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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 60655C38A2D for ; Wed, 26 Oct 2022 00:18:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231476AbiJZAS0 (ORCPT ); Tue, 25 Oct 2022 20:18:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231681AbiJZASY (ORCPT ); Tue, 25 Oct 2022 20:18:24 -0400 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4F58ADCEB6 for ; Tue, 25 Oct 2022 17:18:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1666743503; x=1698279503; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=Rg0wlbaVbTaPsiN6RnFJI6WpQ2cGW1mQ7aVBQk/Fluk=; b=VDB1SzABYi5y7dGR4u9+NoSRbZm1iQXpeXoaXlXVv4G5UlSoOnLP63fI +AJKF8GX46tr+gsuu5aCbr+keV1HcHPfNo5ga0DJzuKaj7fvKEm+Jpl+5 s/etuWGOC+jevbZ+S8zfa6UmSJKH7a7jVGmxMDcpc7K+CC1sg2W4BOVDo FSBBiPEJVsmE0CUCPXymfvi9fBgR7Wlgjf+ttnZ4ZMkMpidTdoaolQl8N SsnTVkEfz4MREvO27LN5pxuakhUgmRWUPAT4oYb8Qi6TR6z9Bwh3xo/0E lEQmMK+CrdEK7HZPZDRy/zFMnBUeT93aVRKdi43YsVdYyj3gEHu8w3uL4 A==; X-IronPort-AV: E=McAfee;i="6500,9779,10511"; a="394136109" X-IronPort-AV: E=Sophos;i="5.95,213,1661842800"; d="scan'208";a="394136109" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Oct 2022 17:18:22 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10511"; a="663000388" X-IronPort-AV: E=Sophos;i="5.95,213,1661842800"; d="scan'208";a="663000388" Received: from dmocuta-mobl2.ger.corp.intel.com (HELO intel.com) ([10.252.44.60]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Oct 2022 17:18:20 -0700 Date: Wed, 26 Oct 2022 02:18:18 +0200 From: Andi Shyti To: "Dixit, Ashutosh" Cc: Andi Shyti , Gwan-gyeong Mun , anshuman.gupta@intel.com, intel-gfx@lists.freedesktop.org, llvm@lists.linux.dev, Nick Desaulniers , linux-kernel@vger.kernel.org Subject: Re: [PATCH] drm/i915/hwmon: Fix a build error used with clang compiler Message-ID: References: <20221024210953.1572998-1-gwan-gyeong.mun@intel.com> <87mt9kppb6.wl-ashutosh.dixit@intel.com> <87ilk7pwrw.wl-ashutosh.dixit@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ilk7pwrw.wl-ashutosh.dixit@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ashutosh, > On Tue, 25 Oct 2022 02:25:06 -0700, Andi Shyti wrote: > > > > Hi Ashutosh, > > Hi Andi :) > > > > > If a non-constant variable is used as the first argument of the FIELD_PREP > > > > macro, a build error occurs when using the clang compiler. > > A "non-constant variable" does not seem to be the cause of the compile > error with clang, see below. > > > > > > > drivers/gpu/drm/i915/i915_hwmon.c:115:16: error: result of comparison of constant 18446744073709551615 with expression of type 'typeof (_Generic((field_msk), char: (unsigned char)0, unsigned char: (unsigned char)0, signed char: (unsigned char)0, unsigned short: (unsigned short)0, short: (unsigned short)0, unsigned int: (unsigned int)0, int: (unsigned int)0, unsigned long: (unsigned long)0, long: (unsigned long)0, unsigned long long: (unsigned long long)0, long long: (unsigned long long)0, default: (field_msk)))' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare] > > > > > > What is 18446744073709551615? You may want to limit the length of this line > > > or checkpatch doesn't complain? > > > > yeah! I am not a clang user, and this must be some ugly error > > output. I don't think it makes sense to break it, though. > > 18446744073709551615 == ~0ull (see use in __BF_FIELD_CHECK). I just wonder, then, where this number comes from, looks to me like an ill formatted constant coming from the compiler (definitely bigger than a ull). > > > > > > bits_to_set = FIELD_PREP(field_msk, nval); > > > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > ./include/linux/bitfield.h:114:3: note: expanded from macro 'FIELD_PREP' > > > > __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \ > > > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > ./include/linux/bitfield.h:71:53: note: expanded from macro '__BF_FIELD_CHECK' > > > > BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) > \ > > So clang seems to break here at this line in __BF_FIELD_CHECK (note ~0ull > also occurs here): > > BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) > \ > __bf_cast_unsigned(_reg, ~0ull), \ > _pfx "type of reg too small for mask"); \ > > So it goes through previous checks including the "mask is not constant" > check. As Nick Desaulniers mentions "__builtin_constant_p is evaluated > after most optimizations have run" so by that time both compilers (gcc and > clang) have figured out that even though _mask is coming in as function > argument it is really the constant below: > > #define PKG_PWR_LIM_1 REG_GENMASK(14, 0) I also thought that the compiler should have figured it out, but then why we got that error, and I don't see how "bf_cast_unsigned(_reg, ~0ull)" could fail. > But it is not clear why clang chokes on this "type of reg too small for > mask" check (and gcc doesn't) since everything is u32. > > It is for this reason I want someone from llvm to chime in. > > > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~ > > > > ./include/linux/build_bug.h:39:58: note: expanded from macro 'BUILD_BUG_ON_MSG' > > > > ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~ > > > > ./include/linux/compiler_types.h:357:22: note: expanded from macro 'compiletime_assert' > > > > _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) > > > > ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > ./include/linux/compiler_types.h:345:23: note: expanded from macro '_compiletime_assert' > > > > __compiletime_assert(condition, msg, prefix, suffix) > > > > ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > ./include/linux/compiler_types.h:337:9: note: expanded from macro '__compiletime_assert' > > > > if (!(condition)) \ > > > > > > > > Fixes: 99f55efb7911 ("drm/i915/hwmon: Power PL1 limit and TDP setting") > > > > Cc: Ashutosh Dixit > > > > Cc: Anshuman Gupta > > > > Cc: Andi Shyti > > > > Signed-off-by: Gwan-gyeong Mun > > > > --- > > > > drivers/gpu/drm/i915/i915_hwmon.c | 12 +++--------- > > > > 1 file changed, 3 insertions(+), 9 deletions(-) > > > > > > > > diff --git a/drivers/gpu/drm/i915/i915_hwmon.c b/drivers/gpu/drm/i915/i915_hwmon.c > > > > index 9e9781493025..782a621b1928 100644 > > > > --- a/drivers/gpu/drm/i915/i915_hwmon.c > > > > +++ b/drivers/gpu/drm/i915/i915_hwmon.c > > > > @@ -101,21 +101,16 @@ hwm_field_read_and_scale(struct hwm_drvdata *ddat, i915_reg_t rgadr, > > > > > > > > static void > > > > hwm_field_scale_and_write(struct hwm_drvdata *ddat, i915_reg_t rgadr, > > > > - u32 field_msk, int nshift, > > > > - unsigned int scale_factor, long lval) > > > > + int nshift, unsigned int scale_factor, long lval) > > > > { > > > > u32 nval; > > > > - u32 bits_to_clear; > > > > - u32 bits_to_set; > > > > > > > > /* Computation in 64-bits to avoid overflow. Round to nearest. */ > > > > nval = DIV_ROUND_CLOSEST_ULL((u64)lval << nshift, scale_factor); > > > > > > > > - bits_to_clear = field_msk; > > > > - bits_to_set = FIELD_PREP(field_msk, nval); > > > > - > > > > hwm_locked_with_pm_intel_uncore_rmw(ddat, rgadr, > > > > - bits_to_clear, bits_to_set); > > > > + PKG_PWR_LIM_1, > > > > + FIELD_PREP(PKG_PWR_LIM_1, nval)); > > > > > > I don't want to give up so easily. We might have future uses for the > > > function where we want field_msk to be passed into the function (rather > > > than set inside the function as in this patch). > > > > > > Do we understand what clang is complaining about? And why this compiles > > > with gcc? > > > > Because we are not compiling the builtin functions with gcc but > > gcc has support for them. The FIELD_PREP checks if the first > > parameter is a constant: > > > > BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), > > > > where _mask was our field_mask, but we ignore it. Apparently > > clang doesn't. > > So we have debunked this above. > > > If we want to stick to gcc only, then I still think the patch is > > correct for two reasons: > > > > 1. it's cleaner > > 2. we would get on with the job and if one day we will decide > > to suppport builtin functions in gcc as well, we will sleep > > peacefully :) > > I disagree with the patch even if we need to fix this in i915 (rather than > say change the headers or something in clang). > > Note that hwm_field_scale_and_write() pairs with hwm_field_read_and_scale() > (they are basically a set/get pair) so it is desirable they have identical > arguments. This patch breaks that symmetry. OK, didn't see it! Makes sense. > If we have to fix this in i915, I prefer the following patch (so just skip > the checks in FIELD_PREP): > > @@ -112,7 +112,7 @@ hwm_field_scale_and_write(struct hwm_drvdata *ddat, i915_reg_t rgadr, > nval = DIV_ROUND_CLOSEST_ULL((u64)lval << nshift, scale_factor); > > bits_to_clear = field_msk; > - bits_to_set = FIELD_PREP(field_msk, nval); > + bits_to_set = (nval << __bf_shf(field_msk)) & field_msk; > > hwm_locked_with_pm_intel_uncore_rmw(ddat, rgadr, doesn't look pretty, though! :/ > But I'd wait to hear from clang/llvm folks first. Yeah! Looking forward to getting some ideas :) Thanks, Ashutosh! Andi > > > Copying llvm@lists.linux.dev too. > > > > maybe llvm folks have a better opinion. > > > > Thanks. > -- > Ashutosh > > > > > } > > > > > > > > /* > > > > @@ -406,7 +401,6 @@ hwm_power_write(struct hwm_drvdata *ddat, u32 attr, int chan, long val) > > > > case hwmon_power_max: > > > > hwm_field_scale_and_write(ddat, > > > > hwmon->rg.pkg_rapl_limit, > > > > - PKG_PWR_LIM_1, > > > > hwmon->scl_shift_power, > > > > SF_POWER, val); > > > > return 0; > > > > -- > > > > 2.37.1 > > > >