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 7FE99EB64DD for ; Thu, 22 Jun 2023 20:36:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230294AbjFVUgI convert rfc822-to-8bit (ORCPT ); Thu, 22 Jun 2023 16:36:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42780 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229961AbjFVUgG (ORCPT ); Thu, 22 Jun 2023 16:36:06 -0400 Received: from gloria.sntech.de (gloria.sntech.de [185.11.138.130]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BC07BDC for ; Thu, 22 Jun 2023 13:36:01 -0700 (PDT) Received: from i53875bdf.versanet.de ([83.135.91.223] 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 1qCR1z-00020C-4S; Thu, 22 Jun 2023 22:35:51 +0200 From: Heiko =?ISO-8859-1?Q?St=FCbner?= To: Palmer Dabbelt , Stefan O'Rear Cc: linux-riscv@lists.infradead.org, samuel@sholland.org, guoren@kernel.org, christoph.muellner@vrull.eu, conor.dooley@microchip.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC 2/2] RISC-V: add T-Head vector errata handling Date: Thu, 22 Jun 2023 22:35:50 +0200 Message-ID: <9132027.CDJkKcVGEf@diego> In-Reply-To: <23381fc8-c297-46ed-9e11-a2643e18e4c9@app.fastmail.com> References: <20230228215435.3366914-1-heiko@sntech.de> <1941316.PYKUYFuaPT@diego> <23381fc8-c297-46ed-9e11-a2643e18e4c9@app.fastmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Stefan, Am Donnerstag, 22. Juni 2023, 20:58:37 CEST schrieb Stefan O'Rear: > On Thu, Jun 22, 2023, at 1:39 PM, Heiko Stübner wrote: > > Am Dienstag, 13. Juni 2023, 08:35:53 CEST schrieb Stefan O'Rear: > >> vxrm and vxsat are part of fcsr in 0.7.1, so they should already have been > >> handled by __fstate_save and __fstate_restore, and this code is likely to > >> misbehave (saving the new process's vxrm/vxsat in the old process's save area > >> because float state is swapped before vector state in __switch_to). > > > > I'm not sure I follow your description but may be overlooking or have > > misunderstood something. > > > > Somehow I way to often have trouble resolving CSR addresses, but according > > to openSBI, FCSR has the location of 0x3 > > (#define CSR_FCSR 0x003 in include/sbi/riscv_encoding.h) > > > > where CSR_VXSAT and CSR_VXRM are at 0x9 and 0xa respectively. > > (#define CSR_VXSAT 0x9 and #define CSR_VXRM 0xa) > > > > > > And looking at __fstate_save + __fstate_restore the only CSRs accessed seem > > to be CSR_STATUS and FCSR itself. > > > > I definitly won't claim to be right, but don't see the issue yet. > > > > > > Thanks for a hint > > Heiko > > Are you aware of "3.7. Vector Fixed-Point Fields in fcsr" in > riscv-v-spec-0.7.1.pdf? oh wow, thanks a lot for that pointer, now I understand your concern. So in vector-0.7.1 fcsr[10:9] mirrors vxrm and fcsr[8] mirrors vxsat. On a positive note, the T-Head cores seem to not implement the full vector 0.7.1 specification after all, in the documentation I have [0] fcsr[31:8] are declared as "0" and uppermost bits are [7:5] for the "frm" field. So I guess a code comment should suffice to explain :-) Regards Heiko [0] https://github.com/T-head-Semi/openc906/blob/main/doc/%E7%8E%84%E9%93%81C906%E7%94%A8%E6%88%B7%E6%89%8B%E5%86%8C.pdf 16.3.1.3 浮点控制状态寄存器（FCSR） on page 334