From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 9A7CCC2D1; Wed, 13 Aug 2025 11:35:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755084939; cv=none; b=AIOLxoGqddJZ51Wa3ObKeIfEP/FvmpDZupkGqF/w/yjppQhiBK5TRn25pS6fSGnGdg7l4w2r4y2E1gcixihzbezcDvDp1hfPPGsdHYYEUQ5vjZwkwBjsUVg9A5SdjFKcW2TtdTux0FZq0XZnkjuGhET4BCeQZ+ufmVrmfaFVE5g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755084939; c=relaxed/simple; bh=Vk9N3hmeSjURiuFT0AuHUJEe3nkb1shrWR3PfY+VcWc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XnFsggm5MbvByNkWfGfZSj2zL6Nt7Xgix1J7nhMH9p7ggscMynPwFOl9tCKgsVRdCfSZNfmRcCGHL3jcR1svy7P0mrRDcUG3Eiarvx2jDnqxZrkIvebZMVa21u/UdrKNYFE8nigia39sS33r/ENHs5RzF+nmPT2+wujFPLrp0hM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 8F0EF12FC; Wed, 13 Aug 2025 04:35:28 -0700 (PDT) Received: from raptor (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 922E53F738; Wed, 13 Aug 2025 04:35:34 -0700 (PDT) Date: Wed, 13 Aug 2025 12:35:31 +0100 From: Alexandru Elisei To: Sudeep Holla Cc: Marc Zyngier , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Lorenzo Pieralisi , Hanjun Guo , "Rafael J. Wysocki" , Daniel Lezcano , Thomas Gleixner , Mark Rutland , alexandru.elisei@arm.com Subject: Re: [PATCH 0/4] clocksource: Add standalone MMIO ARM arch timer driver Message-ID: References: <20250807160243.1970533-1-maz@kernel.org> <20250813-macho-snobbish-alpaca-ff07fa@sudeepholla> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250813-macho-snobbish-alpaca-ff07fa@sudeepholla> Hello, On Wed, Aug 13, 2025 at 11:55:48AM +0100, Sudeep Holla wrote: > +Alexandru > > On Thu, Aug 07, 2025 at 05:02:39PM +0100, Marc Zyngier wrote: > > For the past 10 years, both Mark and I have been lamenting about the > > sorry state of the badly named "arch_timer" driver, and about the way > > the MMIO part is intricately weaved into the system-register part. > > > > The time has finally come to have a stab at it. > > > > This small series simply creates a new timer driver for the MMIO arch > > timer, and only that. It is an actual driver, and not some kludge that > > has to run super early (that's what the per-CPU timers are for). This > > allows, in turn, a pretty large cleanup of the per-CPU driver, though > > there is more to come -- one thing at a time. > > > > As an added bonus, we get a clocksource, which the original code > > didn't provide. Just in case it might be useful. The end-result is far > > more readable, and about 100 lines smaller. > > > > (Tested it on Juno R2 and FVP in both DT and ACPI boot) > > Tested-by: Sudeep Holla > Reviewed-by: Sudeep Holla > > Alexandru found it useful(avoids some unexpected hang IIUC) in his setup > based on bootwrapper which doesn't initialise MMIO timers. Just FYI, this is the testing that I did. Without this series, if firmware (boot-wrapper-aarch64 in my testing) doesn't configure access to the memory-mapped timer: [ 0.000000] arch_timer: Unable to find a suitable frame in timer @ 0x000000002a810000 [ 0.000000] Failed to initialize '/timer@2a810000': -22 .. [ 0.528000] kvm [1]: kvm_arch_timer: uninitialized timecounter .. # ls /dev/kvm ls: cannot access '/dev/kvm': No such file or directory With this series, if firmware doesn't configure access to the memory-mapped timer: [ 0.549399] kvm [1]: Hyp nVHE mode initialized successfully .. [ 2.018050] arch-timer-mmio 2a810000.timer: Unable to find a suitable frame in timer @ 0x000000002a810000 [ 2.018123] arch-timer-mmio 2a810000.timer: probe with driver arch-timer-mmio failed with error -22 .. # ls /dev/kvm /dev/kvm Thanks, Alex