linux-kernel - Re: [PATCH v2 0/22] On-demand device probing

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Date:	Wed, 29 Jul 2015 02:36:33 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:	linux-kernel@...r.kernel.org,
	Stephen Warren <swarren@...dotorg.org>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Mark Brown <broonie@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	devicetree@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-acpi@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	linux-fbdev@...r.kernel.org, linux-usb@...r.kernel.org,
	Felipe Balbi <balbi@...com>, linux-pwm@...r.kernel.org,
	alsa-devel@...a-project.org,
	Terje Bergström <tbergstrom@...dia.com>,
	Len Brown <lenb@...nel.org>, Rob Herring <robh+dt@...nel.org>,
	David Airlie <airlied@...ux.ie>,
	Michael Turquette <mturquette@...libre.com>,
	linux-clk@...r.kernel.org, dmaengine@...r.kernel.org,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Sebastian Reichel <sre@...nel.org>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Grant Likely <grant.likely@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexandre Courbot <gnurou@...il.com>, linux-pm@...r.kernel.org,
	Stephen Boyd <sboyd@...eaurora.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-gpio@...r.kernel.org, Vinod Koul <vinod.koul@...el.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	dri-devel@...ts.freedesktop.org, Lee Jones <lee.jones@...aro.org>,
	linux-tegra@...r.kernel.org, Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Jingoo Han <jingoohan1@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	linux-i2c@...r.kernel.org
Subject: Re: [PATCH v2 0/22] On-demand device probing

On Tuesday, July 28, 2015 03:19:31 PM Tomeu Vizoso wrote:
> Hello,
> 
> I have a problem with the panel on my Tegra Chromebook taking longer
> than expected to be ready during boot (Stéphane Marchesin reported what
> 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.
> 
> 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.
> 
> This basically reuses the information that is already implicit in the
> probe() implementations, saving us from refactoring existing drivers or
> adding information to DTBs.
> 
> 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).
> 
> 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.
> 
> 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.
> 
> We could avoid the above by moving resource storage into the core, but I
> don't think there's a compelling case for that.
> 
> 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).
> 
> 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

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