From: Grant Likely <grant.likely@secretlab.ca> To: David Daney <david.daney@cavium.com> Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Greg Kroah-Hartman <greg@kroah.com>, Dilan Lee <dilee@nvidia.com>, Mark Brown <broonie@opensource.wolfsonmicro.com>, Manjunath GKondaiah <manjunath.gkondaiah@linaro.org>, Arnd Bergmann <arnd@arndb.de> Subject: Re: [RFC PATCH v3] drivercore: Add driver probe deferral mechanism Date: Wed, 12 Oct 2011 22:19:31 -0600 [thread overview] Message-ID: <20111013041931.GH15829@ponder.secretlab.ca> (raw) In-Reply-To: <4E94B01D.2050402@cavium.com> On Tue, Oct 11, 2011 at 02:07:41PM -0700, David Daney wrote: > On 10/11/2011 01:47 PM, Andrew Morton wrote: > >On Thu, 22 Sep 2011 12:51:23 -0600 > >Grant Likely<grant.likely@secretlab.ca> wrote: > > > >>Allow drivers to report at probe time that they cannot get all the resources > >>required by the device, and should be retried at a later time. > >> > >>This should completely solve the problem of getting devices > >>initialized in the right order. Right now this is mostly handled by > >>mucking about with initcall ordering which is a complete hack, and > >>doesn't even remotely handle the case where device drivers are in > >>modules. This approach completely sidesteps the issues by allowing > >>driver registration to occur in any order, and any driver can request > >>to be retried after a few more other drivers get probed. > > > >What happens is there is a circular dependency, or if a driver's > >preconditions are never met? AFAICT the code keeps running the probe > >function for ever. > > > > The deferred probe functions are only run once per (other) driver > binding event. So once you quit registering new drivers, no further > probing is done. There is no endless loop happening here. > > If the preconditions are never met, the driver will just sit in the > list waiting. Plus, as an optimization, walking the deferred list doesn't begin until late initcall time so that the first pass over the device drivers proceeds completely before starting retries. > >If so: bad. The kernel should detect such situations, should > >exhaustively report them and if possible, fix them up and struggle > >onwards. The kernel won't get stalled on deferred probe. It may end up with stale devices in the deferred list, but that only means those particular devices won't get bound to a driver. It isn't fatal. > I don't think we should actively report anything, but being able to > inspect the deferred probe list from user space might be useful for > diagnosing problems Well, we could dump out the remaining deferred devices in sysfs. Alternately the kernel could dump them out to the console log after userspace starts. That would catch conditions where built-in drivers aren't able to initialize their devices. g.
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From: grant.likely@secretlab.ca (Grant Likely) To: linux-arm-kernel@lists.infradead.org Subject: [RFC PATCH v3] drivercore: Add driver probe deferral mechanism Date: Wed, 12 Oct 2011 22:19:31 -0600 [thread overview] Message-ID: <20111013041931.GH15829@ponder.secretlab.ca> (raw) In-Reply-To: <4E94B01D.2050402@cavium.com> On Tue, Oct 11, 2011 at 02:07:41PM -0700, David Daney wrote: > On 10/11/2011 01:47 PM, Andrew Morton wrote: > >On Thu, 22 Sep 2011 12:51:23 -0600 > >Grant Likely<grant.likely@secretlab.ca> wrote: > > > >>Allow drivers to report at probe time that they cannot get all the resources > >>required by the device, and should be retried at a later time. > >> > >>This should completely solve the problem of getting devices > >>initialized in the right order. Right now this is mostly handled by > >>mucking about with initcall ordering which is a complete hack, and > >>doesn't even remotely handle the case where device drivers are in > >>modules. This approach completely sidesteps the issues by allowing > >>driver registration to occur in any order, and any driver can request > >>to be retried after a few more other drivers get probed. > > > >What happens is there is a circular dependency, or if a driver's > >preconditions are never met? AFAICT the code keeps running the probe > >function for ever. > > > > The deferred probe functions are only run once per (other) driver > binding event. So once you quit registering new drivers, no further > probing is done. There is no endless loop happening here. > > If the preconditions are never met, the driver will just sit in the > list waiting. Plus, as an optimization, walking the deferred list doesn't begin until late initcall time so that the first pass over the device drivers proceeds completely before starting retries. > >If so: bad. The kernel should detect such situations, should > >exhaustively report them and if possible, fix them up and struggle > >onwards. The kernel won't get stalled on deferred probe. It may end up with stale devices in the deferred list, but that only means those particular devices won't get bound to a driver. It isn't fatal. > I don't think we should actively report anything, but being able to > inspect the deferred probe list from user space might be useful for > diagnosing problems Well, we could dump out the remaining deferred devices in sysfs. Alternately the kernel could dump them out to the console log after userspace starts. That would catch conditions where built-in drivers aren't able to initialize their devices. g.
next prev parent reply other threads:[~2011-10-13 4:19 UTC|newest] Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-09-22 18:51 [RFC PATCH v3] drivercore: Add driver probe deferral mechanism Grant Likely 2011-09-22 18:51 ` Grant Likely 2011-09-22 18:58 ` Joe Perches 2011-09-22 18:58 ` Joe Perches 2011-09-22 19:28 ` David Daney 2011-09-22 20:29 ` Alan Cox 2011-09-22 20:29 ` Alan Cox 2011-09-22 21:19 ` Grant Likely 2011-09-22 21:19 ` Grant Likely 2011-09-23 17:50 ` Valdis.Kletnieks 2011-09-23 17:50 ` Valdis.Kletnieks at vt.edu 2011-09-23 23:18 ` Grant Likely 2011-09-23 23:18 ` Grant Likely 2011-09-22 21:19 ` David Daney 2011-09-22 22:47 ` Alan Cox 2011-09-22 22:47 ` Alan Cox 2011-09-23 5:02 ` Grant Likely 2011-09-23 5:02 ` Grant Likely 2011-09-23 16:55 ` David Daney 2011-09-23 16:55 ` David Daney 2011-09-26 14:16 ` Mark Brown 2011-09-26 14:16 ` Mark Brown 2011-09-26 15:12 ` Russell King - ARM Linux 2011-09-26 15:12 ` Russell King - ARM Linux 2011-09-26 15:26 ` Mark Brown 2011-09-26 15:26 ` Mark Brown 2011-09-26 15:48 ` Grant Likely 2011-09-26 15:48 ` Grant Likely 2011-09-27 13:50 ` Arnd Bergmann 2011-09-27 13:50 ` Arnd Bergmann 2011-09-27 21:08 ` Grant Likely 2011-09-27 21:08 ` Grant Likely 2011-09-27 22:13 ` Mark Brown 2011-09-27 22:13 ` Mark Brown 2011-09-28 13:04 ` Arnd Bergmann 2011-09-28 13:04 ` Arnd Bergmann 2011-09-28 13:20 ` Mark Brown 2011-09-28 13:20 ` Mark Brown 2011-09-28 23:14 ` Grant Likely 2011-09-28 23:14 ` Grant Likely 2011-09-29 11:00 ` Mark Brown 2011-09-29 11:00 ` Mark Brown 2011-10-03 23:02 ` Kevin Hilman 2011-10-03 23:02 ` Kevin Hilman 2011-10-04 15:52 ` Grant Likely 2011-10-04 15:52 ` Grant Likely 2011-10-04 14:51 ` G, Manjunath Kondaiah 2011-10-04 14:51 ` G, Manjunath Kondaiah 2011-10-04 14:51 ` G, Manjunath Kondaiah 2011-10-04 15:58 ` Grant Likely 2011-10-04 15:58 ` Grant Likely 2011-10-04 15:58 ` Grant Likely 2011-10-04 18:35 ` G, Manjunath Kondaiah 2011-10-04 18:35 ` G, Manjunath Kondaiah 2011-10-04 23:35 ` Grant Likely 2011-10-04 23:35 ` Grant Likely 2011-10-07 3:31 ` G, Manjunath Kondaiah 2011-10-07 3:31 ` G, Manjunath Kondaiah 2011-10-11 20:47 ` Andrew Morton 2011-10-11 20:47 ` Andrew Morton 2011-10-11 21:07 ` David Daney 2011-10-13 4:19 ` Grant Likely [this message] 2011-10-13 4:19 ` Grant Likely
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