From mboxrd@z Thu Jan 1 00:00:00 1970 From: alankao@andestech.com (Alan Kao) Date: Fri, 2 Nov 2018 08:41:22 +0800 Subject: [RFC 0/2] RISC-V: A proposal to add vendor-specific code In-Reply-To: References: <20181101005541.GA25604@andestech.com> Message-ID: <20181102004122.GA22741@andestech.com> To: linux-riscv@lists.infradead.org List-Id: linux-riscv.lists.infradead.org On Thu, Nov 01, 2018 at 10:50:04AM -0700, Palmer Dabbelt wrote: > On Wed, 31 Oct 2018 17:55:42 PDT (-0700), alankao at andestech.com wrote: > >On Wed, Oct 31, 2018 at 07:17:45AM -0700, Christoph Hellwig wrote: > >>On Wed, Oct 31, 2018 at 04:46:10PM +0530, Anup Patel wrote: > >>> I agree that we need a place for vendor-specific ISA extensions and > >>> having vendor-specific directories is also good. > >> > >>The only sensible answer is that we should not allow vendor specific > >>extensions in the kernel at all. ... > > > >How can this even be possible if a extension includes an extra register > >set as some domain-specific context? In such a case, kernel should > >at least process the context during any context switch, just like how it > >deals with the FP context. > > Ya, I think there are cases where vendor-specific extensions are going to be > necessary to handle within the kernel. Right now the only one I can think > of is the performance counter stuff, where we explicitly allow > vendor-specific counters as part of the ISA spec. > > For stateful extensions, we currently have a standard mechanism where the XS > bits get set in sstatus and the actual save/restore code is hidden behind an > SBI call. That call doesn't currently exist, but if we just go ahead and > add one it should be easy to support this from within Linux. We'll need to > figure out how to enable these custom extensions from userspace, but that > seems tractable as well. We'll probably also want some fast-path for the V > extension (and any other stateful standard extensions), but I think as long > as the V extension adds a quick check for dirtiness then it's not a big > deal. > > Do you guys have stateful extensions? We're trying really hard to avoid > them at SiFive because they're a huge headache, so unless there's a > compelling base of software using one I don't want to go add support if we > can avoid it. Currently no, but the future is hard to see. As long as the extensible freedom claimed by the RISC-V foundation remains true, such extensions may have their role to play. Don't worry now, I was just to give a example that in some possible vendor-specific cases the kernel cannot keep itself from involving. 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=-4.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT 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 6A530C0044C for ; Fri, 2 Nov 2018 00:42:27 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 314112084A for ; Fri, 2 Nov 2018 00:42:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="dxWmLctv" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 314112084A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=andestech.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=XH2xldYO2vZjbMrMGq0sI0VZaPFh0z/MTUjslxk1JJQ=; b=dxWmLctvq6qsJN VClAzfyUmzpUsc0hPvJ4COW88Y50xQbSV9eJg8B2RrusRnI69d5QTuzIdUJDIhvIHaCyku53a0dzK vDPRz0tPWy5C8r65GAwV8R4L2UomvLL0H5WW1CZW09r8OBrUpt6McC3dCG8QXA3Z42D7y6eYp8kVL z5EWliRd/k6BI0IL4ZWI8RXyBwgv8F0aG7vM7e2qUpcOkXSYUGumMFuzfBOE+puIsZ6ZMJT/T8iYE kb9aXjT0KEAmRu3v/SSCV83Tzk0ebAuK194yEPvKCWCSoBAPgmPrIILQWtwUNoL30VZc1FD4LL3Zs jlDw0Z10UsR2wFoTk02w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gINXe-0002GM-8j; Fri, 02 Nov 2018 00:42:26 +0000 Received: from 59-120-53-16.hinet-ip.hinet.net ([59.120.53.16] helo=ATCSQR.andestech.com) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gINXY-00027G-Ob for linux-riscv@lists.infradead.org; Fri, 02 Nov 2018 00:42:24 +0000 Received: from mail.andestech.com (atcpcs16.andestech.com [10.0.1.222]) by ATCSQR.andestech.com with ESMTP id wA20g6Nt003936; Fri, 2 Nov 2018 08:42:06 +0800 (GMT-8) (envelope-from alankao@andestech.com) Received: from andestech.com (10.0.15.65) by ATCPCS16.andestech.com (10.0.1.222) with Microsoft SMTP Server id 14.3.123.3; Fri, 2 Nov 2018 08:41:21 +0800 Date: Fri, 2 Nov 2018 08:41:22 +0800 From: Alan Kao To: Palmer Dabbelt Subject: Re: [RFC 0/2] RISC-V: A proposal to add vendor-specific code Message-ID: <20181102004122.GA22741@andestech.com> References: <20181101005541.GA25604@andestech.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Originating-IP: [10.0.15.65] X-DNSRBL: X-MAIL: ATCSQR.andestech.com wA20g6Nt003936 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20181101_174221_286733_1D7CD4E2 X-CRM114-Status: GOOD ( 16.35 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: zong@andestech.com, aou@eecs.berkeley.edu, Arnd Bergmann , greentime@andestech.com, anup@brainfault.org, linux-kernel@vger.kernel.org, Christoph Hellwig , vincentc@andestech.com, linux-riscv@lists.infradead.org, deanbo422@gmail.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org Message-ID: <20181102004122.vGOBQZwqy2VhSw1CyuKRuIsvsH-F90CnsOT9r17fk9Y@z> On Thu, Nov 01, 2018 at 10:50:04AM -0700, Palmer Dabbelt wrote: > On Wed, 31 Oct 2018 17:55:42 PDT (-0700), alankao@andestech.com wrote: > >On Wed, Oct 31, 2018 at 07:17:45AM -0700, Christoph Hellwig wrote: > >>On Wed, Oct 31, 2018 at 04:46:10PM +0530, Anup Patel wrote: > >>> I agree that we need a place for vendor-specific ISA extensions and > >>> having vendor-specific directories is also good. > >> > >>The only sensible answer is that we should not allow vendor specific > >>extensions in the kernel at all. ... > > > >How can this even be possible if a extension includes an extra register > >set as some domain-specific context? In such a case, kernel should > >at least process the context during any context switch, just like how it > >deals with the FP context. > > Ya, I think there are cases where vendor-specific extensions are going to be > necessary to handle within the kernel. Right now the only one I can think > of is the performance counter stuff, where we explicitly allow > vendor-specific counters as part of the ISA spec. > > For stateful extensions, we currently have a standard mechanism where the XS > bits get set in sstatus and the actual save/restore code is hidden behind an > SBI call. That call doesn't currently exist, but if we just go ahead and > add one it should be easy to support this from within Linux. We'll need to > figure out how to enable these custom extensions from userspace, but that > seems tractable as well. We'll probably also want some fast-path for the V > extension (and any other stateful standard extensions), but I think as long > as the V extension adds a quick check for dirtiness then it's not a big > deal. > > Do you guys have stateful extensions? We're trying really hard to avoid > them at SiFive because they're a huge headache, so unless there's a > compelling base of software using one I don't want to go add support if we > can avoid it. Currently no, but the future is hard to see. As long as the extensible freedom claimed by the RISC-V foundation remains true, such extensions may have their role to play. Don't worry now, I was just to give a example that in some possible vendor-specific cases the kernel cannot keep itself from involving. _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv