From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 99395215776; Tue, 4 Feb 2025 16:51:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738687881; cv=none; b=ReTCTI/WcdXNaz+6sxx2d/PRtOBdnNHAt5nEDncw+T84Jg92ScdZ4Z7xXKAKeTydq2580ry+ar6BtJBu9kv0FuSfu6tXrHrvxz9Rx+aJdCzIVFFe7Spz0nYQciR2d38lelUsLph1QCSC+iMElpCuekCvx9yTPl3rBCZN02pmnb4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738687881; c=relaxed/simple; bh=72lyvzbkOWCoWrejdv+Om5NJfaD1Lw1U67vX17qNFN0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jYXEVcTd29/gGDsFqovs09lg0JItKAS9pyxcnYi/J2v9w8I3Fjgljh0MhogiewUFzof1UfIEpwTgbESX7p2NUnV/SD/YBas5wzfsTa1AdBPjCukuvTbLl2OaRcDbG0io8OW3oiD6f2Jo7rPM+TnBZ+7TNNV/xDpYvqqHK+P2s1A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hw+i5l0x; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hw+i5l0x" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3F6A1C4CEDF; Tue, 4 Feb 2025 16:51:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738687881; bh=72lyvzbkOWCoWrejdv+Om5NJfaD1Lw1U67vX17qNFN0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hw+i5l0xwGyxokCg+CsjU84EXKNdTN5eRpo6t0USLhWWFK+nMkbrVfEn7e5FrFtWV RlgAYc8ASrK9JMdRS3L2VwpEECf+J/hcqvrr2we9tq2upNF4LSMB/LLHiOqQ5fsI8S qX2GMIUolB+ThTOetlnqeOXSuOK9qvbL1Y8PZC0d5Z98TV2xq6CKfq6Z+1bRBIdFIk tvtpikgG55bYBeLbXXDWXQhLu5BC2YB5XXmrUdUKZNlI0wqkMbFWhyHlOWxCB0nknt 5L4UNvxdWuPQudGwsG4OQyL8GF2l/C6/lu0zssJVo1NOoO8vP5AnoetVodjamxsrIj 2YcBKbRZ8GM1g== Date: Tue, 4 Feb 2025 10:51:20 -0600 From: Rob Herring To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, "Rafael J. Wysocki" , Danilo Krummrich , Lyude Paul , Alexander Lobakin , Andy Shevchenko , Bjorn Helgaas , Jonathan Cameron , Liam Girdwood , Lukas Wunner , Mark Brown , =?iso-8859-1?Q?Ma=EDra?= Canal , Robin Murphy , Simona Vetter , Zijun Hu , linux-usb@vger.kernel.org, rust-for-linux@vger.kernel.org Subject: Re: [PATCH v2 1/5] driver core: add a faux bus for use when a simple device/bus is needed Message-ID: <20250204165120.GA2994503-robh@kernel.org> References: <2025020421-poster-moisture-534b@gregkh> <2025020424-retrain-recharger-407c@gregkh> <20250204164650.GA2970208-robh@kernel.org> Precedence: bulk X-Mailing-List: rust-for-linux@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: <20250204164650.GA2970208-robh@kernel.org> On Tue, Feb 04, 2025 at 10:46:50AM -0600, Rob Herring wrote: > On Tue, Feb 04, 2025 at 12:09:13PM +0100, Greg Kroah-Hartman wrote: > > Many drivers abuse the platform driver/bus system as it provides a > > simple way to create and bind a device to a driver-specific set of > > probe/release functions. Instead of doing that, and wasting all of the > > memory associated with a platform device, here is a "faux" bus that > > can be used instead. > > > > Signed-off-by: Greg Kroah-Hartman > > --- > > v2: - renamed bus and root device to just "faux" thanks to Thomas > > - removed the one-driver-per-device and now just have one driver > > entirely thanks to Danilo > > - kerneldoc fixups and additions and string handling bounds checks > > hanks to Andy > > - coding style fix thanks to Jonathan > > - tested that the destroy path actually works > > > > drivers/base/Makefile | 2 +- > > drivers/base/base.h | 1 + > > drivers/base/faux.c | 196 ++++++++++++++++++++++++++++++++++++ > > drivers/base/init.c | 1 + > > include/linux/device/faux.h | 31 ++++++ > > 5 files changed, 230 insertions(+), 1 deletion(-) > > create mode 100644 drivers/base/faux.c > > create mode 100644 include/linux/device/faux.h > > > > diff --git a/drivers/base/Makefile b/drivers/base/Makefile > > index 7fb21768ca36..8074a10183dc 100644 > > --- a/drivers/base/Makefile > > +++ b/drivers/base/Makefile > > @@ -6,7 +6,7 @@ obj-y := component.o core.o bus.o dd.o syscore.o \ > > cpu.o firmware.o init.o map.o devres.o \ > > attribute_container.o transport_class.o \ > > topology.o container.o property.o cacheinfo.o \ > > - swnode.o > > + swnode.o faux.o > > obj-$(CONFIG_AUXILIARY_BUS) += auxiliary.o > > obj-$(CONFIG_DEVTMPFS) += devtmpfs.o > > obj-y += power/ > > diff --git a/drivers/base/base.h b/drivers/base/base.h > > index 8cf04a557bdb..0042e4774b0c 100644 > > --- a/drivers/base/base.h > > +++ b/drivers/base/base.h > > @@ -137,6 +137,7 @@ int hypervisor_init(void); > > static inline int hypervisor_init(void) { return 0; } > > #endif > > int platform_bus_init(void); > > +int faux_bus_init(void); > > void cpu_dev_init(void); > > void container_dev_init(void); > > #ifdef CONFIG_AUXILIARY_BUS > > diff --git a/drivers/base/faux.c b/drivers/base/faux.c > > new file mode 100644 > > index 000000000000..9b28643afc45 > > --- /dev/null > > +++ b/drivers/base/faux.c > > @@ -0,0 +1,196 @@ > > +// SPDX-License-Identifier: GPL-2.0-only > > +/* > > + * Copyright (c) 2025 Greg Kroah-Hartman > > + * Copyright (c) 2025 The Linux Foundation > > + * > > + * A "simple" faux bus that allows devices to be created and added > > + * automatically to it. This is to be used whenever you need to create a > > + * device that is not associated with any "real" system resources, and do > > + * not want to have to deal with a bus/driver binding logic. It is > > + * intended to be very simple, with only a create and a destroy function > > + * available. > > + */ > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include "base.h" > > + > > +#define MAX_NAME_SIZE 256 /* Max size of a faux_device name */ > > + > > +/* > > + * Internal wrapper structure so we can hold the memory > > + * for the driver and the name string of the faux device. > > + */ > > +struct faux_object { > > + struct faux_device faux_dev; > > + const struct faux_driver_ops *faux_ops; > > + char name[]; > > +}; > > +#define to_faux_object(dev) container_of_const(dev, struct faux_object, faux_dev.dev) > > + > > +static struct device faux_bus_root = { > > + .init_name = "faux", > > +}; > > + > > +static int faux_match(struct device *dev, const struct device_driver *drv) > > +{ > > + /* Match always succeeds, we only have one driver */ > > + return 1; > > +} > > + > > +static int faux_probe(struct device *dev) > > +{ > > + struct faux_object *faux_obj = to_faux_object(dev); > > + struct faux_device *faux_dev = &faux_obj->faux_dev; > > + const struct faux_driver_ops *faux_ops = faux_obj->faux_ops; > > + int ret = 0; > > + > > + if (faux_ops && faux_ops->probe) > > Is there any use for faux_ops being NULL (or probe being NULL for that > matter)? I can't think of one. So faux_device_create should check that > and fail instead of checking here. NM, I see your converted cases do just that. Weird. I suppose you could still say if faux_ops is not NULL, then probe must not be NULL. Rob