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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8B457C636CC for ; Thu, 16 Feb 2023 11:36:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230269AbjBPLga (ORCPT ); Thu, 16 Feb 2023 06:36:30 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53300 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229554AbjBPLg2 (ORCPT ); Thu, 16 Feb 2023 06:36:28 -0500 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C0D5A311DB for ; Thu, 16 Feb 2023 03:36:26 -0800 (PST) Received: from [192.168.1.100] (2-237-20-237.ip236.fastwebnet.it [2.237.20.237]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: kholk11) by madras.collabora.co.uk (Postfix) with ESMTPSA id 9EAFB66021A4; Thu, 16 Feb 2023 11:36:23 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1676547384; bh=G9BSho1GnSatqIudITCrmTSdqPkXYOoJFWUkVyjCuWc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=MyUu8FB94A0Xm90zVQgHmFH4gauMLWTbAaktc57qXymFPjpzpP3wCNXtNnX+wKuPI agAo7XMul4fd6z9GjzVyIiH8GPrkiYBmgVWOhJ99+ozzkjWcSjaDMmj2aUenx87HVN 6UL6RZ1vexo2EIPuzdTMuEAQ/bP+B2+uBSdxp5ShFlABvfsAZTw7GFmBAGLqpBkhpW FfEI/QX5s87okEdjpO778JFQxKnLBw0S6LNxu92JJbLQDHcxf4Kz9ooDHUkat3P3wP FfCoh2tbfor/X/7zza8KgpvPepEHyhHdUc7LHOJVmBmY1Ju7rLaWHxXxKElUnQzVD3 qlRdpXBCcUS6Q== Message-ID: <26c100f2-bf31-7212-5d13-25b6b14b8f61@collabora.com> Date: Thu, 16 Feb 2023 12:36:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.2 Subject: Re: [PATCH v2 4/4] clocksource/drivers/timer-mediatek: Make timer-mediatek become loadable module To: Matthias Brugger , Sudeep Holla Cc: walter.chang@mediatek.com, Daniel Lezcano , Thomas Gleixner , "Maciej W . Rozycki" , John Stultz , Krzysztof Kozlowski , wsd_upstream@mediatek.com, stanley.chu@mediatek.com, Chun-hung.Wu@mediatek.com, Freddy.Hsin@mediatek.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org References: <20230214105412.5856-1-walter.chang@mediatek.com> <20230214105412.5856-5-walter.chang@mediatek.com> <20230214222021.k3tsfwezhnh7tdlx@bogus> <996b4e61-8486-d939-7367-1240b3c5c5fa@collabora.com> <20230215131849.mcgz53jf24atialp@bogus> <53f0e612-b5cc-262e-df98-add1e8a06573@collabora.com> <20230215144627.ddjc7x365qdnhymi@bogus> <7ac030be-8b5e-d190-6676-8cea9cdc1915@collabora.com> <96d6f405-22bc-f112-2c88-76da280eed46@gmail.com> Content-Language: en-US From: AngeloGioacchino Del Regno In-Reply-To: <96d6f405-22bc-f112-2c88-76da280eed46@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Il 16/02/23 12:23, Matthias Brugger ha scritto: > > > On 16/02/2023 11:22, AngeloGioacchino Del Regno wrote: >> Il 15/02/23 15:46, Sudeep Holla ha scritto: >>> On Wed, Feb 15, 2023 at 02:30:51PM +0100, AngeloGioacchino Del Regno wrote: >>>> >>>> Both. I mean that these platforms do have architected timers, but they are stopped >>>> before the bootloader jumps to the kernel, or they are never started at all. >>>> >>>> Please refer to: >>>> >>>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/clocksource/timer-mediatek.c?h=next-20230215&id=327e93cf9a59b0d04eb3a31a7fdbf0f11cf13ecb >>>> >>>> For a nice explanation. >>>> >>> >>> Thanks for that. Well then I see no point in making these modules if you >>> can't have generic Image that boots on all the platform. I now tend to think >>> that these are made modules just because GKI demands and it *might* work >>> on one or 2 platforms. One we move this as modules, how will be know the >>> Image without these timers or with them built as modules will boot or not >>> on a given mediatek platform. Sorry, I initially saw some point in making >>> these timers as modules but if they are required for boot on some systems >>> then I see no point. So if that is the case, NACK for these as it just >>> creates more confusion after these are merged as why some Images or >>> even why defconfig image(if we push the config change as well) is not >>> booting on these platforms. >>> >>> It is no longer just for system timer useful in low power CPU idle states >>> as I initial thought. >>> >> >> I think that there is still a point in modularization for this driver and I >> can propose a rather simple solution, even though this may add some, rather >> little, code duplication to the mix. >> >> The platforms that I've described (like mt6795) need the system timer to be >> initialized as early as possible - that's true - but that timer is always >> "CPUXGPT". >> >> On those platforms, you *still* have multiple timers: >>   - CPUX (short for cpuxgpt), used only as system timer; >>   - SYST, as another system timer implementation (additional timers) but >>     those are always initialized (AFAIK) from the bootloader before booting; >>   - GPT (General Purpose Timer). >> >> On one SoC, you may have: >>   - CPUX *and* SYST >>   - CPUX *and* GPT >>   - CPUX *and* SYST *and* GPT >> >> ... where the only one that is boot critical and needs to be initialized early >> is always only CPUX. >> >> Hence this proposal: to still allow modularization of timers on MediaTek platforms, >> we could eventually split the CPUX as a separated driver that *cannot be*, due to >> the previously explained constraints, compiled as module, hence always built-in, >> from a timer-mediatek driver that could be a module and capable of handling only >> SYST and GPT timers. >> >> In that case, we'd hence have... >>   - timer-mediatek-cpux.o (bool) >>   - timer-mediatek.c (tristate) >> >> Counting that the CPUX timers are actually even using different `tick_resume` >> and `set_state_shutdown` callbacks (doing only a IRQ clear/restore and nothing >> else), the amount of duplication would be .. well, again, minimal, but then >> this means that timer-mediatek-cpux would be `default y if ARCH_MEDIATEK`, or >> even selected by ARCH_MEDIATEK itself. >> >> If you think that this could be a good solution, I can send a "fast" patch to >> split it out, preparing the ground for the people doing this module work. >> >> Any considerations? >> > > I think your proposal sounds acceptable, but we would need to make sure that all > SoCs can boot with the CPUX driver. I'm aware of some armv7 SoCs that use a kind of > hack to enable the architecture timer [1]. This, for one part, should be moved to > CPUX, if possible. For the other part it makes me wonder if really all supported > MediaTek platforms will boot with SYST/GPT being a module. I think we will need > some effort from the community to test that. > > So as a resume, yes I think your approach is feasible but we should collect > tested-by tags before merging it. > > Regards, > Matthias > > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/mach-mediatek/mediatek.c?h=v6.2-rc8#n16 Right. I completely forgot about those platforms, even though my intention was to actually try and migrate them once the CPUX was picked. My bad. Well, I think that this module conversion will take quite a while, so there should be no need to rush... I'll send a series later with the split *and* a conversion of those platforms, so that we will see a removal of that mediatek_timer_init() function. Some encouraging words ahead: I'm totally confident that the conversion will Just Work, because the MT6795 SoC had the same handling for CPUXGPT as the older MT6589/7623/8127/8135... as that SoC had two implementations initially, one as ARM, one as ARM64. Whatever - let's see what I can come up with, then. Cheers, Angelo