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 53888C48BF6 for ; Mon, 26 Feb 2024 11:05:50 +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-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc: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=OHhobRlQ+HK+8/veukVJu6A3eTXgKjirswdbtrkLZtM=; b=MgpO6GyI8Fo0wA h7oeFuDhM6WT6LcQRz+M1oG2BAHqio6UZLvycsoB3RuVBZshxnnk9tQDKMZLfR2MMDoJrHeVOJJDY 6LA1BW9wTfv1Ud+z7x3F9aLzdlniNdU4JLC9DMadpxh5OufqtkcC6NjcFhAVTTieSZHSJRgpE8mwX j9n39Nw7qQGDVnPVPEj0LwQFxUUnuw40V1bObWnNZ33c1F5Egoaai950eJNMabmmoeEf3TI3IyjOk B4ORjjtUjIpXLSzgJwx++pcLda1iFW+lq+QMmvGkTSvPzw6pkXxjTOKQ7TYREn0ZsRoavq4LaLmNP VbF/2belhVONDZiyq4FQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1reYnd-00000000GsM-0NJD; Mon, 26 Feb 2024 11:05:33 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1reYnZ-00000000GrA-2yZq for linux-arm-kernel@lists.infradead.org; Mon, 26 Feb 2024 11:05:31 +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 A4B9CDA7; Mon, 26 Feb 2024 03:06:03 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.68.53]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EC98B3F6C4; Mon, 26 Feb 2024 03:05:23 -0800 (PST) Date: Mon, 26 Feb 2024 11:04:46 +0000 From: Mark Rutland To: Anshuman Khandual Cc: Will Deacon , linux-arm-kernel@lists.infradead.org, broonie@kernel.org, Catalin Marinas , linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64/hw_breakpoint: Determine lengths from generic perf breakpoint macros Message-ID: References: <20240223113102.4027779-1-anshuman.khandual@arm.com> <20240223125224.GC10641@willie-the-truck> <1901fadb-1d71-4374-be8c-00935bb27854@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1901fadb-1d71-4374-be8c-00935bb27854@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240226_030529_814078_37921399 X-CRM114-Status: GOOD ( 25.52 ) 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Feb 26, 2024 at 08:19:39AM +0530, Anshuman Khandual wrote: > On 2/23/24 18:22, Will Deacon wrote: > > On Fri, Feb 23, 2024 at 05:01:02PM +0530, Anshuman Khandual wrote: > >> Both platform i.e ARM_BREAKPOINT_LEN_X and generic i.e HW_BREAKPOINT_LEN_X > >> macros are used interchangeably to convert event->attr.bp_len and platform > >> breakpoint control arch_hw_breakpoint_ctrl->len. Let's be consistent while > >> deriving one from the other. This does not cause any functional changes. > >> > >> Cc: Will Deacon > >> Cc: Mark Rutland > >> Cc: Catalin Marinas > >> Cc: linux-arm-kernel@lists.infradead.org > >> Cc: linux-kernel@vger.kernel.org > >> Signed-off-by: Anshuman Khandual > >> --- > >> This applies on v6.8-rc5 > >> > >> arch/arm64/kernel/hw_breakpoint.c | 16 ++++++++-------- > >> 1 file changed, 8 insertions(+), 8 deletions(-) > >> > >> diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c > >> index 35225632d70a..1ab9fc865ddd 100644 > >> --- a/arch/arm64/kernel/hw_breakpoint.c > >> +++ b/arch/arm64/kernel/hw_breakpoint.c > >> @@ -301,28 +301,28 @@ static int get_hbp_len(u8 hbp_len) > >> > >> switch (hbp_len) { > >> case ARM_BREAKPOINT_LEN_1: > >> - len_in_bytes = 1; > >> + len_in_bytes = HW_BREAKPOINT_LEN_1; > > > > I don't think we should do this. The HW_BREAKPOINT_LEN_* definitions are > > part of the user ABI and, although they correspond to the length in bytes, > > that's not necessarily something we should rely on. > > Why should not we rely on the user ABI macros if these byte lengths were > initially derived from them. Why should we change the clear: len_in_bytes = 1; ... to the longer, and less clear: len_in_bytes = HW_BREAKPOINT_LEN_1; ... ? > But also there are similar conversions in arch_bp_generic_fields(). Those are specifically for converting from the rch_hw_breakpoint_ctrl encodings to the perf_event_attr encodings. There we don't care about the specific value of the byte, just that we're using the correct encoding. > These hard coded raw byte length numbers seems cryptic, where as in reality > these are just inter converted from generic HW breakpoints lengths. There are three distinct concepts here: 1. The length in bytes, as returned above by get_hbp_len() 2. The length as encoded in the ARM_BREAKPOINT_LEN_* encoding 3. The length as encoded in the HW_BREAKPOINT_LEN_* encoding. I think you're arguing that since 1 and 3 happen to have the values we should treat them as the same thing. I think that Will and I believe that they should be kept distinct because they are distinct concepts. I don't think this needs to change, and can be left as-is. Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel