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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 49411C43441 for ; Tue, 27 Nov 2018 02:47:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E7A8220664 for ; Tue, 27 Nov 2018 02:47:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E7A8220664 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-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728353AbeK0NnV (ORCPT ); Tue, 27 Nov 2018 08:43:21 -0500 Received: from 59-120-53-16.HINET-IP.hinet.net ([59.120.53.16]:13852 "EHLO ATCSQR.andestech.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727621AbeK0NnV (ORCPT ); Tue, 27 Nov 2018 08:43:21 -0500 Received: from mail.andestech.com (atcpcs16.andestech.com [10.0.1.222]) by ATCSQR.andestech.com with ESMTP id wAR2jTVY024938; Tue, 27 Nov 2018 10:45:29 +0800 (GMT-8) (envelope-from vincentc@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; Tue, 27 Nov 2018 10:46:41 +0800 Date: Tue, 27 Nov 2018 10:46:38 +0800 From: Vincent Chen To: David Laight CC: "green.hu@gmail.com" , "arnd@arndb.de" , "linux-kernel@vger.kernel.org" , "Nick Chun-Ming Hu(?????????)" , "deanbo422@gmail.com" Subject: Re: [PATCH v4 2/5] nds32: Support FP emulation Message-ID: <20181127024638.GA6633@andestech.com> References: <1542856478-795-1-git-send-email-vincentc@andestech.com> <1542856478-795-3-git-send-email-vincentc@andestech.com> <20181126012310.GA26621@andestech.com> <3dcd9764570e4565911b74b08513e2d3@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <3dcd9764570e4565911b74b08513e2d3@AcuMS.aculab.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Originating-IP: [10.0.15.65] X-DNSRBL: X-MAIL: ATCSQR.andestech.com wAR2jTVY024938 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 26, 2018 at 06:18:01PM +0800, David Laight wrote: > From: Vincent Chen > > Sent: 26 November 2018 01:23 > > On Fri, Nov 23, 2018 at 06:53:37PM +0800, David Laight wrote: > > > From: Vincent Chen > > > > Sent: 22 November 2018 03:15 > > > > > > > > The Andes FPU coprocessor does not support denormalized number handling. > > > > According to the specification, FPU generates a denorm input exception > > > > that requires the kernel to deal with this instrution operation when it > > > > encounters denormalized operands. Hence an nds32 FPU ISA emulator in the > > > > kernel is required to meet requirement. > > > > > > What does the FPU generate for results near zero? > > > > 1. The calculation result is a denormalized number > > Depending on the state of underflow trap, the FPU will raise an underflow > > exception or flash the result to zero. > > > > 2. One of the operands is a denormalized number > > Depending on the state of the flash-to-zero mode, the FPU will raise a > > denormalized input exception, which is a specific exception of the nds FPU, > > or directly treats the operand as 0. > > You didn't mention (1) in the commit message. > I use two commits to complete the implementation of the FPU emulator in this patch set. The handling for (1) case is in another patch, "nds32: support denormalized result through FP emulator". Sorry, the above description may be misleading. > It ought to be possibly for the exception routine to rescale the values, > re-issue the same FP instruction, then scale the result. > > David > I Agree. The scheme is common when dealing with denormalized numbers, including the softfp module of the kernel used in this patchset. > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) >