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 2593486324; Tue, 4 Feb 2025 16:46:52 +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=1738687612; cv=none; b=RExNjAjZf4c0pOkyIa2FFg4bWShwDcMxmkuLLORO+pMlvUmDYFSxhAUb4ptpiETSi1IHxxDfa323T2ycXpcqFFgG73s1zcTNqrCj5dd9ylZM0qzXwUo0HemArR8jPxsOeAYjQlpBTK6o/FHhbt7Frz2TDVRQ9pxTaWBtnQHVeTg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738687612; c=relaxed/simple; bh=Qpz3C5E8nx1nBIJt7LETgccuu8y3fVUGdXH3J36Ck9k=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CMDeeNXL20s9qrKx+MhQkyCn8D1WDWxaxnFKEDVlSYTxKaSm3CBFi1o243CGf872IEqoWXgjz/mexeb/WPhj9DgOrkcpB0RPqgJ0VwxTWKLNd/OMjmIByyNNEApxvAvdpS3JiPapGcds4doAy3yV5sSsKzJ3+2fnfKRxyEqlA38= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KgzK3u/6; 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="KgzK3u/6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A91FAC4CEE8; Tue, 4 Feb 2025 16:46:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738687612; bh=Qpz3C5E8nx1nBIJt7LETgccuu8y3fVUGdXH3J36Ck9k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KgzK3u/6uvfPU2FUzh3OknpQHyRrmWDOsyGubSrg3Hd89XtJK6P/54sIrytIQ//GD FzHd4EnRqwzjsltx3DUD2lAVwbrSMxhufk0yqgIcYAeOndculJVrO4PDNA7NeTOqlw 7HBiFGOEjy5otxDOlC8olPJFlBbfxMmGCEyo2CbDLGsMJzbI122GjB3C6+mNAYW/aY ivh9yclT/CetOlEH/yxKU4bqPenqDXPn/nn4rNyVzEHM3l5nPatBeV0B3ckKaWp2pe QhxNQgUwpFWBgkPceG+w72ofd6VqGjq3Mf67prrG2GG+ICvqUvoI3nTnL577QGRlP3 oZN1b5wa5ITug== Date: Tue, 4 Feb 2025 10:46:50 -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: <20250204164650.GA2970208-robh@kernel.org> References: <2025020421-poster-moisture-534b@gregkh> <2025020424-retrain-recharger-407c@gregkh> 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: <2025020424-retrain-recharger-407c@gregkh> 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. > + ret = faux_ops->probe(faux_dev); > + > + return ret; > +} > + > +static void faux_remove(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; > + > + if (faux_ops && faux_ops->remove) > + faux_ops->remove(faux_dev); > +} > + > +static const struct bus_type faux_bus_type = { > + .name = "faux", > + .match = faux_match, > + .probe = faux_probe, > + .remove = faux_remove, > +}; > + > +static struct device_driver faux_driver = { > + .name = "faux_driver", > + .bus = &faux_bus_type, > + .probe_type = PROBE_PREFER_ASYNCHRONOUS, > +}; > + > +static void faux_device_release(struct device *dev) > +{ > + struct faux_object *faux_obj = to_faux_object(dev); > + > + kfree(faux_obj); > +} > + > +/** > + * faux_device_create - create and register a faux device and driver > + * @name: name of the device and driver we are adding > + * @faux_ops: struct faux_driver_ops that the new device will call back into, can be NULL > + * > + * Create a new faux device and driver, both with the same name, and > + * register them in the driver core properly. The probe() callback of > + * @faux_ops will be called with the new device that is created for the > + * caller to do something with. > + * > + * Note, when this function is called, the functions specified in struct > + * faux_ops will be called before the function returns, so be prepared for > + * everything to be properly initialized before that point in time. > + * > + * Return: > + * * NULL if an error happened with creating the device > + * * pointer to a valid struct faux_device that is registered with sysfs > + */ > +struct faux_device *faux_device_create(const char *name, struct faux_driver_ops *faux_ops) const struct faux_driver_ops Rob