From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Date: Wed, 29 Jul 2015 00:36:33 +0000 Subject: Re: [PATCH v2 0/22] On-demand device probing Message-Id: <2554489.GlTphZsHuX@vostro.rjw.lan> List-Id: References: <1438089593-7696-1-git-send-email-tomeu.vizoso@collabora.com> In-Reply-To: <1438089593-7696-1-git-send-email-tomeu.vizoso-ZGY8ohtN/8qB+jHODAdFcQ@public.gmane.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable To: Tomeu Vizoso Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Stephen Warren , Javier Martinez Canillas , Mark Brown , Thierry Reding , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Dmitry Torokhov , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linus Walleij , linux-acpi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Arnd Bergmann , linux-fbdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Felipe Balbi , linux-pwm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, alsa-devel-K7yf7f+aM1XWsZ/bQMPhNw@public.gmane.org, Terje =?ISO-8859-1?Q?Bergstr=F6m?= , Len Brown , Rob Herring , David Airlie , Michael Turquette , linux-clk-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, dmaengine-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Jean-Christophe Plagniol-Villard , Sebastian On Tuesday, July 28, 2015 03:19:31 PM Tomeu Vizoso wrote: > Hello, >=20 > I have a problem with the panel on my Tegra Chromebook taking longer > than expected to be ready during boot (St=C3=A9phane Marchesin reported w= hat > is basically the same issue in [0]), and have looked into ordered > probing as a better way of solving this than moving nodes around in the > DT or playing with initcall levels and linking order. >=20 > While reading the thread [1] that Alexander Holler started with his > series to make probing order deterministic, it occurred to me that it > should be possible to achieve the same by probing devices as they are > referenced by other devices. >=20 > This basically reuses the information that is already implicit in the > probe() implementations, saving us from refactoring existing drivers or > adding information to DTBs. >=20 > During review of v1 of this series Linus Walleij suggested that it > should be the device driver core to make sure that dependencies are > ready before probing a device. I gave this idea a try [2] but Mark Brown > pointed out to the logic duplication between the resource acquisition > and dependency discovery code paths (though I think it's fairly minor). >=20 > To address that code duplication I experimented with Arnd's devm_probe > [3] concept of having drivers declare their dependencies instead of > acquiring them during probe, and while it worked [4], I don't think we > end up winning anything when compared to just probing devices on-demand > from resource getters. >=20 > One remaining objection is to the "sprinkling" of calls to > fwnode_ensure_device() in the resource getters of each subsystem, but I > think it's the right thing to do given that the storage of resources is > currently subsystem-specific. >=20 > We could avoid the above by moving resource storage into the core, but I > don't think there's a compelling case for that. >=20 > I have tested this on boards with Tegra, iMX.6, Exynos and OMAP SoCs, > and these patches were enough to eliminate all the deferred probes > (except one in PandaBoard because omap_dma_system doesn't have a > firmware node as of yet). >=20 > With this series I get the kernel to output to the panel in 0.5s, > instead of 2.8s. Can you trim your CC list somewhat, please? I'm definitely going to look at this, but not before then next week. Sorry about that. Thanks, Rafael