[lkml]   [2015]   [Sep]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v4 0/22] On-demand device probing
On 7 September 2015 at 22:50, Rob Herring <> wrote:
> On Mon, Sep 7, 2015 at 7:23 AM, 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
>> of_device_probe() 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, Rockchip 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).
>> Have submitted a branch [5] with only these patches on top of thursday's
>> linux-next to and I don't see any issues that could be
>> caused by them. For some reason it currently has more passes than the
>> version of -next it's based on!
>> With this series I get the kernel to output to the panel in 0.5s,
>> instead of 2.8s.
>> Regards,
>> Tomeu
>> [0]
>> [1]
>> [2]
>> [3]
>> [4]
>> [5]
>> [6]
>> [7]
>> Changes in v4:
>> - Added bus.pre_probe callback so the probes of Primecell devices can be
>> deferred if their device IDs cannot be yet read because of the clock
>> driver not having probed when they are registered. Maybe this goes
>> overboard and the matching information should be in the DT if there is
>> one.
> Seems overboard to me or at least a separate problem.

It's a separate problem but this was preventing the series from
working on a few boards.

> Most clocks have
> to be setup before the driver model simply because timers depend on
> clocks usually.

Yes, but in this case the apb clocks for the primecell devices are
implemented in a normal platform driver (vexpress_osc_driver), instead
of using CLK_OF_DECLARE.



> Rob
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to
> More majordomo info at
> Please read the FAQ at

 \ /
  Last update: 2015-09-08 09:41    [W:0.380 / U:0.004 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site