Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755741AbbLAJZx (ORCPT ); Tue, 1 Dec 2015 04:25:53 -0500 Received: from mailout1.w1.samsung.com ([210.118.77.11]:30347 "EHLO mailout1.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755555AbbLAJZu (ORCPT ); Tue, 1 Dec 2015 04:25:50 -0500 MIME-version: 1.0 Content-type: text/plain; charset=utf-8; format=flowed X-AuditID: cbfec7f5-f79b16d000005389-54-565d679b4a7c Content-transfer-encoding: 8BIT Subject: Re: [PATCH v2 2/4] driver core: handle -EPROBE_DEFER from bus_type.match() To: Ulf Hansson , Tomeu Vizoso References: <1448542190-19498-1-git-send-email-m.szyprowski@samsung.com> <1448542190-19498-3-git-send-email-m.szyprowski@samsung.com> Cc: linux-samsung-soc , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Russell King - ARM Linux , Greg Kroah-Hartman , Kukjin Kim , Krzysztof Kozlowski , Bartlomiej Zolnierkiewicz From: Marek Szyprowski Message-id: <565D679A.6010303@samsung.com> Date: Tue, 01 Dec 2015 10:25:46 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 In-reply-to: X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFvrCLMWRmVeSWpSXmKPExsVy+t/xq7qz02PDDGY+F7HYOGM9q0Xz4vVs Fq9fGFr0P37NbLHp8TVWi8u75rBZzDi/j8ni9mVei761l9gsjq8Nd+DyaGnuYfPYcXcJo8em VZ1sHneu7WHz2D93DbvH5iX1Hn1bVjF6fN4kF8ARxWWTkpqTWZZapG+XwJUx9+UatoLLuhWN zT+ZGxg/KnQxcnJICJhIvPrzmQXCFpO4cG89G4gtJLCUUeL4dC0Qm1dAUOLH5HtANRwczALy EkcuZYOEmQXMJL68PMzaxcgFVP6cUeLGhqNgvcICoRIzH/9kBLFFgOyfj2czQRSdY5R4snIG O4jDLLCbWWLust1MIFVsAoYSXW+72EA28ApoSSy/GgcSZhFQlTja8hfsOFGBGInHi7eygtic AsESN54/Z5/AKDALyX2zEO6bheS+BYzMqxhFU0uTC4qT0nON9IoTc4tL89L1kvNzNzFC4uLr Dsalx6wOMQpwMCrx8EqsjQkTYk0sK67MPcQowcGsJMLrHBMbJsSbklhZlVqUH19UmpNafIhR moNFSZx35q73IUIC6YklqdmpqQWpRTBZJg5OqQbGlXeuGipdy100f68u24/4dnaLxdtjWCLu HOerf7wmpmSutmTxOtd5FevOMOp9WF2xUqm84v7i2h93/nAalu6K+vntS4rftf+WZaotQgUv yphfX5jRIbA5NIB1a9oMx/o3e3Pt7tWIeNzlUw4WzWjizYqV89moatMd0q6rvm7q4fZTQt1H +zYrsRRnJBpqMRcVJwIAJRFQRocCAAA= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5941 Lines: 152 Hello, On 2015-11-30 14:36, Ulf Hansson wrote: > On 26 November 2015 at 13:49, Marek Szyprowski wrote: >> From: Tomeu Vizoso >> >> Lets implementations of the match() callback in struct bus_type to > /s/Lets/Allow > >> return errors and if it's -EPROBE_DEFER then queue the device for >> deferred probing. >> >> This is useful to buses such as AMBA in which devices are registered >> before their matching information can be retrieved from the HW >> (typically because a clock driver hasn't probed yet). >> >> Signed-off-by: Tomeu Vizoso >> Signed-off-by: Marek Szyprowski >> --- >> drivers/base/dd.c | 24 ++++++++++++++++++++++-- >> include/linux/device.h | 2 +- >> 2 files changed, 23 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/base/dd.c b/drivers/base/dd.c >> index a641cf3..a20c119 100644 >> --- a/drivers/base/dd.c >> +++ b/drivers/base/dd.c >> @@ -490,6 +490,7 @@ static int __device_attach_driver(struct device_driver *drv, void *_data) >> struct device_attach_data *data = _data; >> struct device *dev = data->dev; >> bool async_allowed; >> + int ret; >> >> /* >> * Check if device has already been claimed. This may >> @@ -500,8 +501,17 @@ static int __device_attach_driver(struct device_driver *drv, void *_data) >> if (dev->driver) >> return -EBUSY; >> >> - if (!driver_match_device(drv, dev)) >> + ret = driver_match_device(drv, dev); >> + if (!ret) >> return 0; >> + else if (ret < 0) { > Depending on what happens with the added dev_warn() below, perhaps a > switch statement can make it a bit clearer, instead of these messy if > clauses? Frankly, I have no idea how to convert this to switch statement and make the code easier to read. Please note that we have the following 4 cases: ret > 0: positive match ret == 0: negative match ret == -EPROBE_DEFER: deferred probe ret < 0: other, unknown error Another way to encode this logic is the following code: if (ret == 0) { /* no match */ return 0; } else if (ret == -EPROBE_DEFER) { dev_dbg(dev, "Device match requests probe deferral\n"); driver_deferred_probe_add(dev); return ret; } else if (ret < 0) { dev_dbg(dev, "Bus failed to match device: %d", ret); return ret; } /* ret > 0 means positive match */ >> + if (ret == -EPROBE_DEFER) { >> + dev_dbg(dev, "Device match requests probe deferral\n"); >> + driver_deferred_probe_add(dev); >> + } else >> + dev_warn(dev, "Bus failed to match device: %d", ret); > Greg commented on this before, as it may introduce some noise [1]. > > I started browsing various bus’s implementation of the ->match() > callback. A quick search tells me that most implementations are > following the Documentation/driver-model/porting.txt, which means > returning 0 or 1. Actually I couldn't find anyone returning any other > value, though it was a quick search. > > On the other hand, include/linux/device.h states a "non-zero" value is > allowed to be return, so there's a tiny conflict between the code and > the documentation. I guess we should fix that!? Okay, I will update the documentation as well. > No matter what, I realize that it could be useful to print a message > when receiving a negative error code, maybe dev_dbg() could be > sufficient? > >> + return ret; >> + } >> >> async_allowed = driver_allows_async_probing(drv); >> >> @@ -621,6 +631,7 @@ void device_initial_probe(struct device *dev) >> static int __driver_attach(struct device *dev, void *data) >> { >> struct device_driver *drv = data; >> + int ret; >> >> /* >> * Lock device and try to bind to it. We drop the error >> @@ -632,8 +643,17 @@ static int __driver_attach(struct device *dev, void *data) >> * is an error. >> */ >> >> - if (!driver_match_device(drv, dev)) >> + ret = driver_match_device(drv, dev); >> + if (!ret) >> + return 0; >> + else if (ret < 0) { >> + if (ret == -EPROBE_DEFER) { >> + dev_dbg(dev, "Device match requests probe deferral\n"); >> + driver_deferred_probe_add(dev); >> + } else >> + dev_warn(dev, "Bus failed to match device: %d", ret); >> return 0; >> + } >> >> if (dev->parent) /* Needed for USB */ >> device_lock(dev->parent); >> diff --git a/include/linux/device.h b/include/linux/device.h >> index b8f411b..d4e7d1f 100644 >> --- a/include/linux/device.h >> +++ b/include/linux/device.h >> @@ -70,7 +70,7 @@ extern void bus_remove_file(struct bus_type *, struct bus_attribute *); >> * @dev_groups: Default attributes of the devices on the bus. >> * @drv_groups: Default attributes of the device drivers on the bus. >> * @match: Called, perhaps multiple times, whenever a new device or driver >> - * is added for this bus. It should return a nonzero value if the >> + * is added for this bus. It should return a positive value if the >> * given device can be handled by the given driver. >> * @uevent: Called when a device is added, removed, or a few other things >> * that generate uevents to add the environment variables. >> -- >> 1.9.2 Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/