From patchwork Thu May 4 18:14:24 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Conor Dooley X-Patchwork-Id: 13231485 X-Patchwork-Delegate: palmer@dabbelt.com 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 463A0C7EE22 for ; Thu, 4 May 2023 18:15:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; 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=Iy+xjypgiqNQIdE0ltygqM8zJH3WGY5VU51CaW9yQZw=; b=RvlhPyqum6o++L 3Mi6G29RXyxwrkLVJ/DxW8K1S4iFbLIro+jy8X9A7CHBr0jpJSr2JX21vf5NpJV4hyDvRkKdlw+8r rCxQDBj1pevVFmJBtG5RmF5+nFvVBRWBcOpevQPAfZ4YjntCzvGlo+S+dHhdro05nLAW+F4unv9vK YdrFYM8GivOc2w/LKUqQTwm9eBdfWIV5MUSpzvO+O9G0AQFGFxgPouAbG7Zn719Pv5zQQf6bphBa8 cmN1CNFz5ATun3Su1zmRfbkLRXsm8FhS5zqd2Qi6o/Yop0QBhaj7fIfsLa/6Fd6B62vPmDwtdddis bsLJGYTjsXvDEMUQvfiw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1pudUX-008VSr-00; Thu, 04 May 2023 18:15:45 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1pudUU-008VRq-1r for linux-riscv@lists.infradead.org; Thu, 04 May 2023 18:15:44 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1E57D63582; Thu, 4 May 2023 18:15:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CD7B2C4339B; Thu, 4 May 2023 18:15:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1683224141; bh=TvakAFbPcrD7hCAm+Dg/e0/oiiwwCFYHsXJHt4QwDVU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aYV8cmJ1Nnhh/W+VHZmFjvwGW8ajy5UhBaGSd4K9KMTU1m6WEd22OZhJwTmWLCiUS /U47uDUQP3thiwl/0X7ZtePbL+S4zjkN2WPV5yPwQ+x2mdxxCs90pUJshkoFkczN/v DZtwEPSIbnbiDu2NB7rhWgiz8ziid6xaVk9udcUah6kT8kZ4GhB5o+HrPZz+YuaOfH kc3pZSiVN80atvP/0wPQYuPNJ0HYlWBxpHL9LgmkWQj0Hs+rtVbfXE1KVohmfLX6rb SpnoXIy/NFeHXG8WuP3TQKZZ7RO68D8aqChYHrh69IyDI9gGrAzB6biJwaAtVf5ro7 CiGROdaUwKlhQ== From: Conor Dooley To: palmer@dabbelt.com Subject: [PATCH v1 5/7] RISC-V: rework comments in ISA string parser Date: Thu, 4 May 2023 19:14:24 +0100 Message-Id: <20230504-never-childlike-75e2ce7e50d8@spud> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230504-divisive-unsavory-5a2ff0c3c2d1@spud> References: <20230504-divisive-unsavory-5a2ff0c3c2d1@spud> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4630; i=conor.dooley@microchip.com; h=from:subject:message-id; bh=tEHbqETiBb82U3DYdAGcDcmKm/YUwFV3nz4D77zk+xA=; b=owGbwMvMwCFWscWwfUFT0iXG02pJDCnBX/8FOB89s3/6Pg6x5TZTo7U3ZxXKFLhecdTK7E+fI 91RH2rZUcrCIMbBICumyJJ4u69Fav0flx3OPW9h5rAygQxh4OIUgImYnWNkmBj0WG/eIoaSG7vY 8tznzfxw+J/wggmtak+axIQFZ+++vYnhn4FiQmuD/3xfO/WYHIO1Xd1BrXr+4vF/iyzKD7U62cU wAQA= X-Developer-Key: i=conor.dooley@microchip.com; a=openpgp; fpr=F9ECA03CF54F12CD01F1655722E2C55B37CF380C X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230504_111542_685979_DD7AA688 X-CRM114-Status: GOOD ( 23.81 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: conor@kernel.org, Yangyu Chen , Conor Dooley , Paul Walmsley , linux-riscv@lists.infradead.org, Andrew Jones Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org From: Conor Dooley I have found these comments to not be at all helpful whenever I look at the parser. Further, the comments in the default case (single letter parser) are not quite right either. Group the comments into a larger one at the start of each case, that attempts to explain things at a higher level. Signed-off-by: Conor Dooley Reviewed-by: Andrew Jones --- arch/riscv/kernel/cpufeature.c | 71 ++++++++++++++++++++++++++++------ 1 file changed, 60 insertions(+), 11 deletions(-) diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index a79c5c52a174..2fc72f092057 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -146,7 +146,7 @@ void __init riscv_fill_hwcap(void) switch (*ext) { case 's': - /** + /* * Workaround for invalid single-letter 's' & 'u'(QEMU). * No need to set the bit in riscv_isa as 's' & 'u' are * not valid ISA extensions. It works until multi-letter @@ -163,53 +163,102 @@ void __init riscv_fill_hwcap(void) case 'X': case 'z': case 'Z': + /* + * Before attempting to parse the extension itself, we find its end. + * As multi-letter extensions must be split from other multi-letter + * extensions with an "_", the end of a multi-letter extension will + * either be the null character as of_property_read_string() returns + * null-terminated strings, or the "_" at the start of the next + * multi-letter extension. + * + * Next, as the extensions version is currently ignored, we + * eliminate that portion. This is done by parsing backwards from + * the end of the extension, removing any numbers. This may be a + * major or minor number however, so the process is repeated if a + * minor number was found. + * + * ext_end is intended to represent the first character *after* the + * name portion of an extension, but will be decremented to the last + * character itself while eliminating the extensions version number. + * A simple re-increment solves this problem. + */ ext_long = true; - /* Multi-letter extension must be delimited */ for (; *isa && *isa != '_'; ++isa) if (unlikely(!isalnum(*isa))) ext_err = true; - /* Parse backwards */ + ext_end = isa; if (unlikely(ext_err)) break; + if (!isdigit(ext_end[-1])) break; - /* Skip the minor version */ + while (isdigit(*--ext_end)) ; - if (tolower(ext_end[0]) != 'p' - || !isdigit(ext_end[-1])) { - /* Advance it to offset the pre-decrement */ + + if (tolower(ext_end[0]) != 'p' || !isdigit(ext_end[-1])) { ++ext_end; break; } - /* Skip the major version */ + while (isdigit(*--ext_end)) ; + ++ext_end; break; default: + /* + * Things are a little easier for single-letter extensions, as they + * are parsed forwards. + * + * After checking that our starting position is valid, we need to + * ensure that, when isa was incremented at the start of the loop, + * that it arrived at the start of the next extension. + * + * If we are already on a non-digit, there is nothing to do. Either + * we have a multi-letter extension's _, or the start of an + * extension. + * + * Otherwise we have found the current extension's major version + * number. Parse past it, and a subsequent p/minor version number + * if present. The `p` extension must not appear immediately after + * a number, so there is no fear of missing it. + * + */ if (unlikely(!isalpha(*ext))) { ext_err = true; break; } - /* Find next extension */ + if (!isdigit(*isa)) break; - /* Skip the minor version */ + while (isdigit(*++isa)) ; + if (tolower(*isa) != 'p') break; + if (!isdigit(*++isa)) { --isa; break; } - /* Skip the major version */ + while (isdigit(*++isa)) ; + break; } + + /* + * The parser expects that at the start of an iteration isa points to the + * character before the start of the next extension. This will not be the + * case if we have just parsed a single-letter extension and the next + * extension is not a multi-letter extension prefixed with an "_". It is + * also not the case at the end of the string, where it will point to the + * terminating null character. + */ if (*isa != '_') --isa;