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 8226FC9832A for ; Tue, 29 Sep 2026 14:35:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=xXsyG1nJZcjvmXOLppTmlV6HL6GNJEk1tug38gOX6l0=; b=rDkfaFAFfWcnknVZO+QNhkPMUE x5cNmgVyz2+SmOK+jBmY+c41kaA2dbrd5VW0F1ZnubF6sjM19u9VPvZiF4JYiWHtC+0syLrU6RZPo eULYpcv7lbYP5m2Y3kYQtRzxt8i1oRQdESmcdj3+PLEsz6O3AyMld8UVTtqyJ2kRope1Eer/jmKFU tYuy0bHgQ0aAYfgpiYWni1zckkgTtFtPPD7PSWcN6tZIwadITddDkDinVOkO5xCfGhQxCcqW8IK3q LYIeOj2pTLbsrVCv4rxsc4GY2m9yh8Z+pCQ1l0UP8OGd+Au3BFi6cpOvaLoczRwhOmAVH5hMoPoOV uYQIXseA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xBYvS-00000003nrK-0q1g; Tue, 29 Sep 2026 14:35:22 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xBYvR-00000003nqx-0r2o for linux-arm-kernel@lists.infradead.org; Tue, 29 Sep 2026 14:35:21 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id D7EF4410A8; Tue, 29 Sep 2026 14:35:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 22A5C1F000FF; Tue, 29 Sep 2026 14:35:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790692520; bh=xXsyG1nJZcjvmXOLppTmlV6HL6GNJEk1tug38gOX6l0=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=IjUdSti5PbGtpxTH9nZfpeWsbi0bAFEBEQgVElcuOKCzN/zvZsmvUgJnM3NZTIrRg jamQRDL4Fe/VVJ9P+xNWfOHSSnFU/6jmptwUAdy5KFKjsjofxgATg6Y1INB59K1ybn OjPd5zkLzYCyEETvR8VmutueNwMipWkvSozbzc/x6e62Tak2Roh7MIHekVrEw7LWVT 4qIw5AzDUpDcX0/5pGM6av4aj62QuRCCoe+62hiIn5nyUY91XGRCzdj5LRZf0j+Kdq LKX/5DyBFT5UquYEqIibMnIMbnwYwX4vtKkHKmFAW91Ui21mjMgQS+M3wM+xhXYH5M veB8hha56G79g== Date: Tue, 29 Sep 2026 15:35:16 +0100 From: Will Deacon To: Marc Zyngier Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Catalin Marinas , Mark Rutland , Thomas Gleixner , Ben Horgan , Daniel Lezcano Subject: Re: [PATCH v3 7/8] clocksource/drivers/arm_arch_timer: Expose a direct accessor for the virtual counter Message-ID: References: <20260802165327.385217-1-maz@kernel.org> <20260802165327.385217-8-maz@kernel.org> <868q4k3zds.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <868q4k3zds.wl-maz@kernel.org> 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Sep 29, 2026 at 03:28:47PM +0100, Marc Zyngier wrote: > On Tue, 29 Sep 2026 13:55:30 +0100, > Will Deacon wrote: > > > > On Sun, Aug 02, 2026 at 05:53:26PM +0100, Marc Zyngier wrote: > > > We allow access to the architected counter via arch_timer_read_counter(). > > > However, this accessor can either be the virtual or the physical > > > view of the counter, depending on how the kernel has been booted. > > > > > > At the same time, we have some architectural features (such as WFIT, > > > WFET) that rely on the virtual counter, and nothing else. > > > > > > If implementations were perfect, we'd rely on reading CNTVCT_EL0, > > > and be done with it. However, we have a bunch of broken implementations > > > in the wild, which rely on preemption being disabled and other > > > costly workarounds. > > > > > > In order to provide decent performance on non-broken HW while still > > > supporting the legacy horrors, expose arch_timer_read_vcounter() as > > > a new helper that hides this complexity. Obviously, this is simply > > > a global alias of arch_counter_get_cntvct(). > > > > > > Signed-off-by: Marc Zyngier > > > --- > > > drivers/clocksource/arm_arch_timer.c | 2 ++ > > > include/clocksource/arm_arch_timer.h | 1 + > > > 2 files changed, 3 insertions(+) > > > > > > diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c > > > index b3b31d4f4815f..9c7501ce57073 100644 > > > --- a/drivers/clocksource/arm_arch_timer.c > > > +++ b/drivers/clocksource/arm_arch_timer.c > > > @@ -128,6 +128,8 @@ static notrace u64 arch_counter_get_cntvct(void) > > > return __arch_counter_get_cntvct(); > > > } > > > > > > +u64 arch_timer_read_vcounter(void) __attribute__((alias("arch_counter_get_cntvct"))); > > > > nit: compiler-attributes.h provides __alias to make this a tiny bit cleaner. > > > > That said, why did you decide on the alias rather than just having this > > as a wrapper function? > > No idea. Laziness, probably. > > But I've paged most of this stuff out, and I'm not sure it even serves > a purpose, given that we've lived for about a decade with the problem > it tries to solve. > > Consider it an abandoned series. Ok, but patch one is probably worth taking to fix the PMU issue, no? Will