From: Haren Myneni Subject: Re: Crypto/nx842: Ignore invalid XER[S0] return error Date: Sat, 12 Dec 2015 15:01:26 -0800 Message-ID: <566CA746.1090001@linux.vnet.ibm.com> References: <1449891029.19568.5.camel@hbabu-laptop> <20151212084348.GA26552@gate.crashing.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: herbert@gondor.apana.org.au, ddstreet@ieee.org, davem@davemloft.net, mpe@ellerman.id.au, pair@us.ibm.com, linuxppc-dev@lists.ozlabs.org, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org To: Segher Boessenkool Return-path: Received: from e19.ny.us.ibm.com ([129.33.205.209]:33868 "EHLO e19.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751421AbbLLXBn (ORCPT ); Sat, 12 Dec 2015 18:01:43 -0500 Received: from localhost by e19.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 12 Dec 2015 18:01:42 -0500 In-Reply-To: <20151212084348.GA26552@gate.crashing.org> Sender: linux-crypto-owner@vger.kernel.org List-ID: On 12/12/2015 12:43 AM, Segher Boessenkool wrote: > On Fri, Dec 11, 2015 at 07:30:29PM -0800, Haren Myneni wrote: >> NX842 coprocessor sets 3rd bit in CR register with XER[S0] which is >> nothing to do with NX request. On powerpc, XER[S0] will be set if >> overflow in FPU and stays until another floating point operation is >> executed. Since this bit can be set with other valuable return status, >> ignore this XER[S0] value. > > XER[SO] is the *integer* summary overflow bit. It is set by OE=1 > instructions ("addo" and the like), and can only be cleared explicitly > (using "mtxer"). Thanks for the correct description. I was told XER[S0] is floating overflow from FPU. > > The floating point overflow bit is FPSCR[OX]. > >> + /* >> + * NX842 coprocessor sets 3rd bit in CR register with XER[S0]. >> + * Setting XER[S0] happens if overflow in FPU and stays until >> + * other floating operation is executed. XER[S0] value is nothing >> + * to NX and no use to user. Since this bit can be set with other >> + * return values, ignore this error. >> + */ >> + if (ret & ICSWX_XERS0) >> + ret &= ~ICSWX_XERS0; > > You can just always clear it, there is no need to check if it is set first. Do you mean reset this before calling NX? I believe NX coprocessor should not set CR bit as XER[S0] nothing to do with NX request and it is no use. NX is copying this CR bit with XER. But reset XER[S0] has to be done before NX request. We can not do this in icswx since this instruction can be used by other coprocessors in future. But I am not comfortable clearing as we are not touching this XER in the driver or result of NX operation. So I am proposing this patch to fix this not proper NX behaviour - ignores CR bit. If you are OK, I can repost the patch with proper description. Thanks Haren > > > Segher >