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 D5A6EECAAD3 for ; Fri, 9 Sep 2022 14:18:34 +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-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To:Subject: MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=JUNA8ypyVZRovTcTnRmWUjCThbPj0ZaHHn9GESTuHJg=; b=B0enCweKFzR0gN 4yqqg5o/zHK3ZRvNzZs0NnEVhYtDHnHbvpA1vqBocag/xVgYiumcTRFGuNiA2gZbWdzfYhuKsHjrK wa/iyCalLKOAeNNOvK2jmXMg2HyGNJF9ySqzhqdfCIYDwYDu4YJWLA093807NxJ684r6Yh5UPXSNg AjweNC4fh8sbxDHQLsZJwiafQp7QLYuKat50kWwyZkW79gXznwHN36XcmpRPbwQoukp7ITlK3EAnB WUPnI08zU2M4OgPXxP4kWU5U9tob516fxk7/4g++pLF04Z/kx8ZggaMhvUXkWCCfyv+iucvHGlmGV vqc/5cnLlIN6QMCaH5Aw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oWepA-00GfGG-4J; Fri, 09 Sep 2022 14:17:40 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oWeov-00GfAA-UV for linux-arm-kernel@lists.infradead.org; Fri, 09 Sep 2022 14:17:28 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1676C165C; Fri, 9 Sep 2022 07:17:29 -0700 (PDT) Received: from [10.57.15.197] (unknown [10.57.15.197]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E170B3F93E; Fri, 9 Sep 2022 07:17:20 -0700 (PDT) Message-ID: <28b35935-4e7f-2bd5-dda5-ed81402a527e@arm.com> Date: Fri, 9 Sep 2022 15:17:15 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: [PATCH] Report support for optional ARMv8.2 half-precision floating point extension Content-Language: en-GB To: George Pee Cc: Russell King , "Russell King (Oracle)" , Catalin Marinas , "Kirill A. Shutemov" , Austin Kim , Ard Biesheuvel , Mike Rapoport , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20220901141307.2361752-1-georgepee@gmail.com> From: Robin Murphy In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220909_071726_151271_6E49834A X-CRM114-Status: GOOD ( 25.60 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2022-09-09 14:34, George Pee wrote: > Adding the hwcap was part of the diagnosis process-- I added it just > to make sure that the cpu in question supported the optional > extension. > It seems like it could be useful to be able to check for support in > /proc/cpuinfo. Sure, but "support" is about more than just what happens to be present in hardware. Observe that you can build the 32-bit kernel with CONFIG_VFP=n, and it then does not report and VFP or NEON hwcaps, because those features will not be usable in that configuration, even if you know the hardware implements them. Note that this looks different on arm64, since there we always expect to have FPSIMD hardware available, so support in the kernel is unconditional, plus that kernel support is also a lot simpler since we don't have a soft-float ABI with all the corresponding trapping stuff either. It might just be the case here that the call_fpe logic needs a bit of tweaking to provide proper support, but I'm not sufficiently familiar with the ARM VFP code in general to be sure. Thanks, Robin. > On Fri, Sep 9, 2022 at 7:46 AM Robin Murphy wrote: >> >> On 2022-09-01 15:13, george pee wrote: >>> Report as fphp to be consistent with arm64 >> >> Wasn't the original problem that the VFP support code doesn't understand >> the new FP16 instruction encodings, so in practice they don't actually >> work reliably? Exposing a hwcap to say they're functional doesn't >> inherently make them functional - if there is already another patch >> somewhere for that, it should be made clear that this depends on it. >> >> Robin. >> >>> Signed-off-by: george pee >>> --- >>> arch/arm/include/uapi/asm/hwcap.h | 1 + >>> arch/arm/kernel/setup.c | 1 + >>> arch/arm/vfp/vfpmodule.c | 2 ++ >>> 3 files changed, 4 insertions(+) >>> >>> diff --git a/arch/arm/include/uapi/asm/hwcap.h b/arch/arm/include/uapi/asm/hwcap.h >>> index 990199d8b7c6..f975845ce5d3 100644 >>> --- a/arch/arm/include/uapi/asm/hwcap.h >>> +++ b/arch/arm/include/uapi/asm/hwcap.h >>> @@ -28,6 +28,7 @@ >>> #define HWCAP_IDIV (HWCAP_IDIVA | HWCAP_IDIVT) >>> #define HWCAP_LPAE (1 << 20) >>> #define HWCAP_EVTSTRM (1 << 21) >>> +#define HWCAP_FPHP (1 << 22) >>> >>> /* >>> * HWCAP2 flags - for elf_hwcap2 (in kernel) and AT_HWCAP2 >>> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c >>> index 1e8a50a97edf..6694ced0552a 100644 >>> --- a/arch/arm/kernel/setup.c >>> +++ b/arch/arm/kernel/setup.c >>> @@ -1249,6 +1249,7 @@ static const char *hwcap_str[] = { >>> "vfpd32", >>> "lpae", >>> "evtstrm", >>> + "fphp", >>> NULL >>> }; >>> >>> diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c >>> index 2cb355c1b5b7..cef8c64ce8bd 100644 >>> --- a/arch/arm/vfp/vfpmodule.c >>> +++ b/arch/arm/vfp/vfpmodule.c >>> @@ -831,6 +831,8 @@ static int __init vfp_init(void) >>> >>> if ((fmrx(MVFR1) & 0xf0000000) == 0x10000000) >>> elf_hwcap |= HWCAP_VFPv4; >>> + if ((fmrx(MVFR1) & 0x0f000000) == 0x03000000) >>> + elf_hwcap |= HWCAP_FPHP; >>> } >>> /* Extract the architecture version on pre-cpuid scheme */ >>> } else { _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel