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 CE21C132492; Thu, 25 Jul 2024 13:14:14 +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=1721913257; cv=none; b=MIQpQsaWmWKbW5lUVnn8CIfTQos769PQwAwIxuPJFs4VtwqKElSq733DIjvAmthKzPUGg2nemTh0ALIhMlrQ/a37VzCkyry2mrMSjO56OP+YCInQO/KsMR68RxhgCWUksPUmt8Yw1vw9S5244SL0BeOdBoyfV6zgE+Ca4v0G3PA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721913257; c=relaxed/simple; bh=wEVHxiu3Gg6fXP3+WspO2QY7d4BxcqzBopV5kKhQhqQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=X8ILxIvKX1gdYyekHj+prK5WpG80wYu8NgLV/56rjz8fKFKDthJGMQ7OR9nWMUa/O/6R4XyaK4w6ddLZIfRWt94Ft/lb52LsuzyiqnuQ08rKM/qVHA0QHA4XGdBipwCoj8ZSYaBrpawCl6frgZp+tGYC4pKmHFNYNUsSXp1dPpA= 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 5A0C31007; Thu, 25 Jul 2024 06:14:39 -0700 (PDT) Received: from [10.1.29.30] (e122027.cambridge.arm.com [10.1.29.30]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 672373F5A1; Thu, 25 Jul 2024 06:14:12 -0700 (PDT) Message-ID: <28d1989a-106d-4cae-81a9-a7bcc8a474f5@arm.com> Date: Thu, 25 Jul 2024 14:14:10 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] module: Add hard dependencies as syntactic sugar To: Dragan Simic , linux-modules@vger.kernel.org Cc: mcgrof@kernel.org, linux-kernel@vger.kernel.org, didi.debian@cknow.org, Boris Brezillon , Qiang Yu References: <04e0676b0e77c5eb69df6972f41d77cdf061265a.1721906745.git.dsimic@manjaro.org> From: Steven Price Content-Language: en-GB In-Reply-To: <04e0676b0e77c5eb69df6972f41d77cdf061265a.1721906745.git.dsimic@manjaro.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 25/07/2024 12:37, Dragan Simic wrote: > Panfrost and Lima DRM drivers use devfreq to perform DVFS, which is supported > on the associated platforms, while using simple_ondemand devfreq governor by > default. This makes the simple_ondemand module a hard dependency for both > Panfrost and Lima, because the presence of the simple_ondemand module in an > initial ramdisk allows the initialization of Panfrost or Lima to succeed. > This is currently expressed using MODULE_SOFTDEP. [1][2] Please see commits > 80f4e62730a9 ("drm/panfrost: Mark simple_ondemand governor as softdep") and > 0c94f58cef31 ("drm/lima: Mark simple_ondemand governor as softdep") for > additional background information. > > With the addition of MODULE_WEAKDEP in commit 61842868de13 ("module: create > weak dependecies"), the dependency between Panfrost/Lima and simple_ondemand > can be expressed in a much better way as a weakdep, because that provides > the required dependency information to the utilities that generate initial > ramdisks, but leaves the actual loading of the required kernel module(s) to > the kernel. However, being able to actually express this as a hard module > dependency would still be beneficial. > > With all this in mind, let's add MODULE_HARDDEP as some kind of syntactic > sugar, currently implemented as an alias for MODULE_WEAKDEP, so the actual > hard module dependencies can be expressed properly, and possibly handled > differently in the future, avoiding the need to go back, track and churn > all such instances of hard module dependencies. The first consumers of > MODULE_HARDDEP will be the Panfrost and Lima DRM drivers, but the list of > consumers may also grow a bit in the future. > > For example, allowing reduction of the initial ramdisk size is a possible > future difference between handling the MODULE_WEAKDEP and MODULE_HARDDEP > dependencies. When the size of the initial ramdisk is limited, the utilities > that generate initial ramdisks can use the distinction between the weakdeps > and the harddeps to safely omit some of the weakdep modules from the created > initial ramdisks, and to keep all harddep modules. > > Due to the nature of MODULE_WEAKDEP, the above-described example will also > require some additional device-specific information to be made available to > the utilities that create initial ramdisks, so they can actually know which > weakdep modules can be safely pruned for a particular device, but the > distinction between the harddeps and the weakdeps opens up a path towards > using such additional "pruning information" in a more robust way, by ensuring > that the absolutely required harddep modules aren't pruned away. > > [1] https://lore.kernel.org/dri-devel/4e1e00422a14db4e2a80870afb704405da16fd1b.1718655077.git.dsimic@manjaro.org/T/#u > [2] https://lore.kernel.org/dri-devel/fdaf2e41bb6a0c5118ff9cc21f4f62583208d885.1718655070.git.dsimic@manjaro.org/T/#u > > Cc: Steven Price > Cc: Boris Brezillon > Cc: Qiang Yu > Signed-off-by: Dragan Simic Thanks Dragan, while there's obviously a bunch more work to hook this up appropriately, this at least lets drivers signal the actual requirement. Reviewed-by: Steven Price Steve > --- > include/linux/module.h | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/include/linux/module.h b/include/linux/module.h > index 88ecc5e9f523..40e5762847a9 100644 > --- a/include/linux/module.h > +++ b/include/linux/module.h > @@ -179,6 +179,14 @@ extern void cleanup_module(void); > */ > #define MODULE_WEAKDEP(_weakdep) MODULE_INFO(weakdep, _weakdep) > > +/* > + * Hard module dependencies. Currently handled the same as weak > + * module dependencies, but intended to mark hard dependencies > + * as such for possible different handling in the future. > + * Example: MODULE_HARDDEP("module-foo") > + */ > +#define MODULE_HARDDEP(_harddep) MODULE_WEAKDEP(_harddep) > + > /* > * MODULE_FILE is used for generating modules.builtin > * So, make it no-op when this is being built as a module