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 18C4EC54EBD for ; Mon, 9 Jan 2023 19:50:53 +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:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=nLEOQiHZNeFgd1l9TuuZxABbfFwgXTqPFrUFX3op4tY=; b=nUjB6Xf3J3rkWa Bzhjr60VJGvj/C6g7eMmRdyIY58Yrdaquy8xFHRKBfxCB975u/QF7zAHKpomj4AHWQI7qNkRe/xiR XY40K8BWqn9Ot33mWSwzXDDZxMClKTpGZRfdpfOMyjAZZ2Q//kJoZI/og/+GkdWsiPMkt5vlP4t91 NL5+K07pjiZsHTtqo+czvOsIQHCQZZjvCqJXVWvgF+YlfM4EEJRZ170acmslhCIsWck0+dPcELTkn rXUARp2NdPQhRqNy51XhAc/ijZhv9y7inrQbs0tmRZYGmxuCbOp5F02sEwlH/FSI3xgPwf1AokpdF RV1qnIbOD7gsWYPuYGbw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pEyAP-003jLx-GY; Mon, 09 Jan 2023 19:50:45 +0000 Received: from gloria.sntech.de ([185.11.138.130]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pEyAM-003jKD-S5 for linux-riscv@lists.infradead.org; Mon, 09 Jan 2023 19:50:44 +0000 Received: from ip5b412258.dynamic.kabel-deutschland.de ([91.65.34.88] helo=diego.localnet) by gloria.sntech.de with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1pEyAH-0006Kp-CW; Mon, 09 Jan 2023 20:50:37 +0100 From: Heiko =?ISO-8859-1?Q?St=FCbner?= To: Andrew Jones , palmer@dabbelt.com, Conor Dooley Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org Subject: Re: [PATCH v1 0/5] RISC-V Hardware Probing User Interface Date: Mon, 09 Jan 2023 20:50:36 +0100 Message-ID: <2876870.k3LOHGUjKi@diego> In-Reply-To: References: <20221013163551.6775-1-palmer@rivosinc.com> <20221201160614.xpomlqq2fzpzfmcm@kamzik> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230109_115042_944314_F468021B X-CRM114-Status: GOOD ( 58.89 ) 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: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org Hey, Am Montag, 9. Januar 2023, 19:47:17 CET schrieb Conor Dooley: > 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. from my further optimization pov, I just rebased Palmer's v1 forward, as I essentially only want the has-fast-unaligned property from it ;-) . The series I posted today is essentially the basics for "everyone with zbb" and I have a second part on top of that and Palmers hw-probing series that then does the further case. I do hope to get that finalized tomorrow or wednesday. Heiko > 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. > > > > > > 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. > > > > > > 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. > > > > > > 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. > > > > Hi Palmer, > > > > 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. > > > > .../features/zicbom > > .../features/zihintpause > > .../features/sscofpmf > > > > 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. > > > > Properties of extensions are just sub-nodes, some with standard names, > > like > > > > .../features/zicbom/major > > .../features/zicbom/minor > > > > and others, which are cpu feature specific, like > > > > .../features/zicbom/block_size > > > > 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. > > > > Thanks, > > drew > > > > > > > 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. > > > > > > 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. > > > > > > These are also up at kernel.org/palmer/linux/riscv-hwprobe-v1 in case > > > that's easier for folks. > > > > > > > > > > > > _______________________________________________ > > > linux-riscv mailing list > > > linux-riscv@lists.infradead.org > > > http://lists.infradead.org/mailman/listinfo/linux-riscv > > > > _______________________________________________ > > linux-riscv mailing list > > linux-riscv@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-riscv > _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv