From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.manjaro.org (mail.manjaro.org [116.203.91.91]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DA8FC161337; Tue, 18 Jun 2024 19:22:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=116.203.91.91 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718738574; cv=none; b=LvbuWVVjhzMD13IRLZOOMwMXDkMXC1vSosmQ/Y+EFnfmM8N2hY4K765FpA9ytVLLkMwzLGXwYwJ4q0kbccbpzsH9CKSVzCGtR+sxSsqmphkYh1rpsUZGfj+FHTD/ehS6g6Wv6Vw5NK7f79zo2JP1b9e7G0kmFL1VFSo6CWMv/EU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718738574; c=relaxed/simple; bh=0GTVP0n4L+W/rAV9EWsaAj3clwPwkcDwsyMzV91BxBg=; h=MIME-Version:Date:From:To:Cc:Subject:In-Reply-To:References: Message-ID:Content-Type; b=Tbqy5GEjH1wajN2qSvJxLS55OgjIp9Sml2So9FdyhIvfM/ydyZFI4oGgPiNJNfmjsOQGdCkP5L/uA5+f9AYKls65W22dpCbjmMVmKHpXz0OCaYOl+mJFJ6xtVb8X81jlFIFwYnBEzFwCJlGwlRWNn++Jf0npmwZb5WIqK5vs1jA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=manjaro.org; spf=pass smtp.mailfrom=manjaro.org; dkim=pass (2048-bit key) header.d=manjaro.org header.i=@manjaro.org header.b=qTj7h2ep; arc=none smtp.client-ip=116.203.91.91 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=manjaro.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=manjaro.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=manjaro.org header.i=@manjaro.org header.b="qTj7h2ep" Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=manjaro.org; s=2021; t=1718738563; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=s4YEiz4CBg8DZRVTp+VuaQ0rG9uMs+Fd4su7Kzv7iYE=; b=qTj7h2epsVQlF8Iz993/KkiSXK6uhcwkUPlSoemxGPa8B1XTfFPPXhG2zqet0ce3Q/6eXR 3U33xZTdOWbxJZgd9CiM2NnYf+Cgm21ygIzSRfBEUh88MP9eSPL1M3yhOlY+lIeMgDw1Ej swiFfh5RO32RXzZx0aC6UzSoonjT0TK1vkm1/6W/sWIa+SLim+rJ5seWU8gK4g/BFaGtF7 60IkrozZsSPzCgVPXenT6B6lT/9d3dQP1qSOceHBIGxydXyMgABnrNmqncRytFj+nLbNWZ sgOdon7tBhl5UWjuDMZxg7vZgzLcWKTkV//n4HhVzqWNpWPtzlKse1nYyTnkdw== Date: Tue, 18 Jun 2024 21:22:42 +0200 From: Dragan Simic To: Maxime Ripard Cc: Qiang Yu , dri-devel@lists.freedesktop.org, lima@lists.freedesktop.org, maarten.lankhorst@linux.intel.com, tzimmermann@suse.de, airlied@gmail.com, daniel@ffwll.ch, linux-kernel@vger.kernel.org, Philip Muller , Oliver Smith , Daniel Smith , stable@vger.kernel.org Subject: Re: [PATCH] drm/lima: Mark simple_ondemand governor as softdep In-Reply-To: <4813a6885648e5368028cd822e8b2381@manjaro.org> References: <20240618-great-hissing-skink-b7950e@houat> <4813a6885648e5368028cd822e8b2381@manjaro.org> Message-ID: <457ae7654dba38fcd8b50e38a1275461@manjaro.org> X-Sender: dsimic@manjaro.org Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Authentication-Results: ORIGINATING; auth=pass smtp.auth=dsimic@manjaro.org smtp.mailfrom=dsimic@manjaro.org On 2024-06-18 12:33, Dragan Simic wrote: > Hello Qiang and Maxime, > > On 2024-06-18 10:13, Maxime Ripard wrote: >> On Tue, Jun 18, 2024 at 04:01:26PM GMT, Qiang Yu wrote: >>> On Tue, Jun 18, 2024 at 12:33 PM Qiang Yu wrote: >>> > >>> > I see the problem that initramfs need to build a module dependency chain, >>> > but lima does not call any symbol from simpleondemand governor module. >>> > softdep module seems to be optional while our dependency is hard one, >>> > can we just add MODULE_INFO(depends, _depends), or create a new >>> > macro called MODULE_DEPENDS()? > > I had the same thoughts, because softdeps are for optional module > dependencies, while in this case it's a hard dependency. Though, > I went with adding a softdep, simply because I saw no better option > available. > >>> This doesn't work on my side because depmod generates modules.dep >>> by symbol lookup instead of modinfo section. So softdep may be our >>> only >>> choice to add module dependency manually. I can accept the softdep >>> first, then make PM optional later. > > I also thought about making devfreq optional in the Lima driver, > which would make this additional softdep much more appropriate. > Though, I'm not really sure that's a good approach, because not > having working devfreq for Lima might actually cause issues on > some devices, such as increased power consumption. > > In other words, it might be better to have Lima probing fail if > devfreq can't be initialized, rather than having probing succeed > with no working devfreq. Basically, failed probing is obvious, > while a warning in the kernel log about no devfreq might easily > be overlooked, causing regressions on some devices. > >> It's still super fragile, and depends on the user not changing the >> policy. It should be solved in some other, more robust way. > > I see, but I'm not really sure how to make it more robust? In > the end, some user can blacklist the simple_ondemand governor > module, and we can't do much about it. > > Introducing harddeps alongside softdeps would make sense from > the design standpoint, but the amount of required changes wouldn't > be trivial at all, on various levels. After further investigation, it seems that the softdeps have already seen a fair amount of abuse for what they actually aren't intended, i.e. resolving hard dependencies. For example, have a look at the commit d5178578bcd4 (btrfs: directly call into crypto framework for checksumming) [1] and the lines containing MODULE_SOFTDEP() at the very end of fs/btrfs/super.c. [2] If a filesystem driver can rely on the abuse of softdeps, which admittedly are a bit fragile, I think we can follow the same approach, at least for now. With all that in mind, I think that accepting this patch, as well as the related Panfrost patch, [3] should be warranted. I'd keep investigating the possibility of introducing harddeps in form of MODULE_HARDDEP() and the related support in kmod project, similar to the already existing softdep support, [4] but that will inevitably take a lot of time, both for implementing it and for reaching various Linux distributions, which is another reason why accepting these patches seems reasonable. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d5178578bcd4 [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/btrfs/super.c#n2593 [3] https://lore.kernel.org/dri-devel/4e1e00422a14db4e2a80870afb704405da16fd1b.1718655077.git.dsimic@manjaro.org/ [4] https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/commit/?id=49d8e0b59052999de577ab732b719cfbeb89504d