From: Pingfan Liu <kernelfans@gmail.com>
To: rafael@kernel.org
Cc: lukas@wunner.de, linux-kernel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Grygorii Strashko <grygorii.strashko@ti.com>,
Christoph Hellwig <hch@infradead.org>,
Bjorn Helgaas <helgaas@kernel.org>,
Dave Young <dyoung@redhat.com>,
linux-pci@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-pm@vger.kernel.org, kishon@ti.com
Subject: Re: [PATCHv3 0/4] drivers/base: bugfix for supplier<-consumer ordering in device_kset
Date: Sat, 7 Jul 2018 12:24:26 +0800 [thread overview]
Message-ID: <CAFgQCTsCjkDWJsNog_sTnS-ZaZ87fMFpKq1ekVSUG4MDs6K_jw@mail.gmail.com> (raw)
In-Reply-To: <CAFgQCTugu5XO06_xXb4ihkdfGJxtFX0813g2J-Jk2JeYtPP1vA@mail.gmail.com>
On Fri, Jul 6, 2018 at 9:55 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> On Fri, Jul 6, 2018 at 4:47 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >
> > On Fri, Jul 6, 2018 at 10:36 AM, Lukas Wunner <lukas@wunner.de> wrote:
> > > [cc += Kishon Vijay Abraham]
> > >
> > > On Thu, Jul 05, 2018 at 11:18:28AM +0200, Rafael J. Wysocki wrote:
> > >> OK, so calling devices_kset_move_last() from really_probe() clearly is
> > >> a mistake.
> > >>
> > >> I'm not really sure what the intention of it was as the changelog of
> > >> commit 52cdbdd49853d doesn't really explain that (why would it be
> > >> insufficient without that change?)
> > >
> > > It seems 52cdbdd49853d fixed an issue with boards which have an MMC
> > > whose reset pin needs to be driven high on shutdown, lest the MMC
> > > won't be found on the next boot.
> > >
> > > The boards' devicetrees use a kludge wherein the reset pin is modelled
> > > as a regulator. The regulator is enabled when the MMC probes and
> > > disabled on driver unbind and shutdown. As a result, the pin is driven
> > > low on shutdown and the MMC is not found on the next boot.
> > >
> > > To fix this, another kludge was invented wherein the GPIO expander
> > > driving the reset pin unconditionally drives all its pins high on
> > > shutdown, see pcf857x_shutdown() in drivers/gpio/gpio-pcf857x.c
> > > (commit adc284755055, "gpio: pcf857x: restore the initial line state
> > > of all pcf lines").
> > >
> > > For this kludge to work, the GPIO expander's ->shutdown hook needs to
> > > be executed after the MMC expander's ->shutdown hook.
> > >
> > > Commit 52cdbdd49853d achieved that by reordering devices_kset according
> > > to the probe order. Apparently the MMC probes after the GPIO expander,
> > > possibly because it returns -EPROBE_DEFER if the vmmc regulator isn't
> > > available yet, see mmc_regulator_get_supply().
> > >
> > > Note, I'm just piecing the information together from git history,
> > > I'm not responsible for these kludges. (I'm innocent!)
> >
> > Sure enough. :-)
> >
> > In any case, calling devices_kset_move_last() in really_probe() is
> > plain broken and if its only purpose was to address a single, arguably
> > kludgy, use case, let's just get rid of it in the first place IMO.
> >
> Yes, if it is only used for a single use case.
>
Think it again, I saw other potential issue with the current code.
device_link_add->device_reorder_to_tail() can break the
"supplier<-consumer" order. During moving children after parent's
supplier, it ignores the order of child's consumer. Beside this,
essentially both devices_kset_move_after/_before() and
device_pm_move_after/_before() expose the shutdown order to the
indirect caller, and we can not expect that the caller can not handle
it correctly. It should be a job of drivers core. It is hard to
extract high dimension info and pack them into one dimension
linked-list. And in theory, it is warranted that the shutdown seq is
correct by using device tree info. More important, it is cheap with
the data structure in hand. So I think it is time to resolve the issue
once for all.
Thanks and regards,
Pingfan
next prev parent reply other threads:[~2018-07-07 4:24 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-03 6:50 [PATCHv3 0/4] drivers/base: bugfix for supplier<-consumer ordering in device_kset Pingfan Liu
2018-07-03 6:50 ` [PATCHv3 1/4] drivers/base: fold the routine of device's shutdown into a func Pingfan Liu
2018-07-03 6:50 ` [PATCHv3 2/4] drivers/base: utilize device tree info to shutdown devices Pingfan Liu
2018-07-03 7:51 ` Lukas Wunner
2018-07-03 9:26 ` Pingfan Liu
2018-07-04 3:10 ` Pingfan Liu
2018-07-03 10:58 ` Andy Shevchenko
2018-07-03 17:03 ` Pavel Tatashin
2018-07-04 17:04 ` kbuild test robot
2018-07-05 10:11 ` Rafael J. Wysocki
2018-07-06 3:02 ` Pingfan Liu
2018-07-06 9:53 ` Rafael J. Wysocki
2018-07-07 4:02 ` Pingfan Liu
2018-07-06 10:00 ` [PATCH] driver core: Drop devices_kset_move_last() call from really_probe() Rafael J. Wysocki
2018-07-09 13:57 ` Bjorn Helgaas
2018-07-09 21:35 ` Rafael J. Wysocki
2018-07-09 22:06 ` Bjorn Helgaas
2018-07-10 6:19 ` Kishon Vijay Abraham I
2018-07-10 10:32 ` Rafael J. Wysocki
2018-07-10 10:29 ` Rafael J. Wysocki
2018-07-10 6:33 ` Pingfan Liu
2018-07-10 11:35 ` [PATCH] driver core: Partially revert "driver core: correct device's shutdown order" Rafael J. Wysocki
2018-07-10 12:22 ` Kishon Vijay Abraham I
2018-07-10 12:38 ` Rafael J. Wysocki
2018-07-10 12:51 ` [PATCH v2] " Rafael J. Wysocki
2018-07-10 12:59 ` Greg Kroah-Hartman
2018-07-10 15:40 ` Rafael J. Wysocki
2018-07-10 15:47 ` Greg Kroah-Hartman
2018-07-10 19:13 ` Kishon Vijay Abraham I
2018-07-03 6:50 ` [PATCHv3 3/4] drivers/base: clean up the usage of devices_kset_move_last() Pingfan Liu
2018-07-03 14:26 ` Rafael J. Wysocki
2018-07-04 4:40 ` Pingfan Liu
2018-07-04 10:17 ` Rafael J. Wysocki
2018-07-05 2:32 ` Pingfan Liu
2018-07-03 6:50 ` [PATCHv3 4/4] Revert "driver core: correct device's shutdown order" Pingfan Liu
2018-07-03 14:35 ` [PATCHv3 0/4] drivers/base: bugfix for supplier<-consumer ordering in device_kset Rafael J. Wysocki
2018-07-04 2:47 ` Pingfan Liu
2018-07-04 10:21 ` Rafael J. Wysocki
2018-07-05 2:44 ` Pingfan Liu
2018-07-05 9:18 ` Rafael J. Wysocki
2018-07-06 8:36 ` Lukas Wunner
2018-07-06 8:47 ` Rafael J. Wysocki
2018-07-06 13:55 ` Pingfan Liu
2018-07-07 4:24 ` Pingfan Liu [this message]
2018-07-08 8:25 ` Rafael J. Wysocki
2018-07-09 6:48 ` Pingfan Liu
2018-07-09 7:48 ` Rafael J. Wysocki
2018-07-09 8:40 ` Pingfan Liu
2018-07-09 8:58 ` Rafael J. Wysocki
2018-07-06 10:02 ` Kishon Vijay Abraham I
2018-07-06 13:52 ` Pingfan Liu
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