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 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 3A178C54EBD for ; Mon, 9 Jan 2023 18:48:07 +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-Type: List-Subscribe:List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id: In-Reply-To:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Reply-To:Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date :Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=9ntMpi/YcepVxbc8kQEo7XaIdRYXnNrB7UQIsMGEqT8=; b=fCpoWtN6zG6fBfXE7BoNUAR7Y0 x1FUPVNipNUC58AwsG6UF5hmuBWKw73ho0QqwlT3vezCYXir/6fISN5FpwfsaZITPLFK+WafbfcZy EutioAYSbGO8SRYDR6UYlBD6+EPM484pmFmhk/DOhyPFLsbDjwAXg976FKf4O9gK3ppyB2d8ViSPL NvQt+As+5WKtwOcZ2f6Xuuza1P27EViXYATApJIE/KGbz/aStxgzS6CEzr613z4Bhxc6Opirni0kv e0VHGB3UjDxi4ZPPXL0cn9vDgNh9JNJUrcxWVZWpY1kwW6X4Qyubz27GSyFR5SWfU4kzjEAkncd8Z nL5UTVvw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pExBf-003Q9d-1g; Mon, 09 Jan 2023 18:47:59 +0000 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pExB6-003PsI-7h for linux-riscv@lists.infradead.org; Mon, 09 Jan 2023 18:47:26 +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 ams.source.kernel.org (Postfix) with ESMTPS id 9C9A0B80ED9; Mon, 9 Jan 2023 18:47:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1ADCAC433EF; Mon, 9 Jan 2023 18:47:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1673290041; bh=fP3rFASz2vA5R2Ej0f1j1SUqauKXUClyVmaFuzPcWvo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=W/mZrOoPW+KN1IGcmO4c0HseyDY/MFy/9lpepeyTKv3ofInPXt6j4B4GeF6o2lr1w RYtQfHkEajszatUhjB3S2zHpMjqyJmbyCi63NLrlhZpsdyo1eMByBhpgy5sdSAoJeo DeUd4i1D6B1Gzar+JcqH2T+fivbQ/7BJNzj5u0xea3PO0RMkOz0GqjsIVFfHun4qAg KJdfurMP+CuqNnvs9T7Qcalq5lrd9u+TRSkxx77Y3pakn/59whDlOh6GwZ+9SBgXWR dlONaw0FometM7Kvdhrd6MSiWgB0Z81ca05e2Rab7lWQXit4RbO25Z+Wk2ZJSohU7M h+0iVKbb2pFQQ== Date: Mon, 9 Jan 2023 18:47:17 +0000 From: Conor Dooley To: Andrew Jones , palmer@dabbelt.com, heiko@sntech.de Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org Subject: Re: [PATCH v1 0/5] RISC-V Hardware Probing User Interface Message-ID: References: <20221013163551.6775-1-palmer@rivosinc.com> <20221201160614.xpomlqq2fzpzfmcm@kamzik> MIME-Version: 1.0 In-Reply-To: <20221201160614.xpomlqq2fzpzfmcm@kamzik> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230109_104724_609604_82227117 X-CRM114-Status: GOOD ( 53.47 ) 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: , Content-Type: multipart/mixed; boundary="===============9158744654484529811==" Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org --===============9158744654484529811== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="XEybHnosMf+YVb6M" Content-Disposition: inline --XEybHnosMf+YVb6M Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hey! Just bringing this up somewhere a bit more visible than the weekly pw sync-up yoke! I just got my VisionFive2 today & I see Heiko has just posted another version of Zbb support series, right as I had started typing this in fact, so I'm curious where we stand. There's gonna be quite a few people with Zba/Zbb capable hardware soon by the looks of things, so it'd be nice to have something we can point people at that actually applies to recent kernels. I know Palmer you said you'd do some work on it over Christmas, but since that didn't materialise - are you still planning on spinning up a v2? Some thoughts on Drew's sysfs suggestion below would probably be useful if you aren't. Thanks, Conor. On Thu, Dec 01, 2022 at 05:06:14PM +0100, Andrew Jones wrote: > On Thu, Oct 13, 2022 at 09:35:46AM -0700, Palmer Dabbelt wrote: > > These are very much up for discussion, as it's a pretty big new user > > interface and it's quite a bit different from how we've historically > > done things: this isn't just providing an ISA string to userspace, this > > has its own format for providing information to userspace. > >=20 > > There's been a bunch of off-list discussions about this, including at > > Plumbers. The original plan was to do something involving providing an > > ISA string to userspace, but ISA strings just aren't sufficient for a > > stable ABI any more: in order to parse an ISA string users need the > > version of the specifications that the string is written to, the version > > of each extension (sometimes at a finer granularity than the RISC-V > > releases/versions encode), and the expected use case for the ISA string > > (ie, is it a U-mode or M-mode string). That's a lot of complexity to > > try and keep ABI compatible and it's probably going to continue to grow, > > as even if there's no more complexity in the specifications we'll have > > to deal with the various ISA string parsing oddities that end up all > > over userspace. > >=20 > > Instead this patch set takes a very different approach and provides a se > > of key/value pairs that encode various bits about the system. The big > > advantage here is that we can clearly define what these mean so we can > > ensure ABI stability, but it also allows us to encode information that's > > unlikely to ever appear in an ISA string (see the misaligned access > > performance, for example). The resulting interface looks a lot like > > what arm64 and x86 do, and will hopefully fit well into something like > > ACPI in the future. > >=20 > > The actual user interface is a syscall. I'm not really sure that's the > > right way to go about this, but it makes for flexible prototying. > > Various other approaches have been talked about like making HWCAP2 a > > pointer, having a VDSO routine, or exposing this via sysfs.=20 >=20 > Hi Palmer, >=20 > To throw my two cents into the penny jar, I'd vote for sysfs. It handles > the heterogeneous CPU case since cpu feature nodes can be hung off each > cpu node. It also avoids yet another encoding. If we enumerate extensions > and their properties then we need to maintain that enumeration in both > the kernel space and userspace. If, OTOH, we use sysfs node names for > the encoding, then, when we match the spec naming exactly, e.g. >=20 > .../features/zicbom > .../features/zihintpause > .../features/sscofpmf >=20 > userspace can look for features by name. Userspace libraries can even > lead the kernel in development, since the encoding (the spec name) is > already agreed. >=20 > Properties of extensions are just sub-nodes, some with standard names, > like >=20 > .../features/zicbom/major > .../features/zicbom/minor >=20 > and others, which are cpu feature specific, like >=20 > .../features/zicbom/block_size >=20 > I used 'features' in the above examples for the node name, rather than > 'isa', since not all features map to isa extensions, but it should be > possible to fit non-isa features into the same framework. >=20 > Thanks, > drew >=20 >=20 > > Those seem > > like generally reasonable approaches, but I've yet to figure out a way > > to get the general case working without a syscall as that's the only way > > I've come up with to deal with the heterogenous CPU case. Happy to hear > > if someone has a better idea, though, as I don't really want to add a > > syscall if we can avoid it. > >=20 > > I threw this together during the conferences so I would be surprised if > > it's not broken, but I figured it'd be best to just get something on the > > lists sooner rather that later. Happy to have someone go fix my code, > > but the new uABI is really going to be the tricky bit here. There's > > some test code included, but I haven't even booted a kernel with these > > patches so YMMV. > >=20 > > These are also up at kernel.org/palmer/linux/riscv-hwprobe-v1 in case > > that's easier for folks. > >=20 > >=20 > >=20 > > _______________________________________________ > > linux-riscv mailing list > > linux-riscv@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-riscv >=20 > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv --XEybHnosMf+YVb6M Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQRh246EGq/8RLhDjO14tDGHoIJi0gUCY7xhNQAKCRB4tDGHoIJi 0i+3AP99CGIIxzm7kabqvlgGq6Xf4wIK63ZCaAKhBJ2rb3QdJQEA1wP74iiXvIOq j/DJbaiuh9JAIVJ/AxXUj5yBbc80MQg= =VOMS -----END PGP SIGNATURE----- --XEybHnosMf+YVb6M-- --===============9158744654484529811== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv --===============9158744654484529811==--