On 8/19/19 1:49 PM, Saravana Kannan wrote:

On Mon, Aug 19, 2019 at 10:16 AM Frank Rowand [off-list ref] wrote:

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On 8/15/19 6:50 PM, Saravana Kannan wrote:

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On Wed, Aug 7, 2019 at 7:06 PM Frank Rowand [off-list ref] wrote:

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On 7/23/19 5:10 PM, Saravana Kannan wrote:

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Add device-links after the devices are created (but before they are
probed) by looking at common DT bindings like clocks and
interconnects.

< very big snip (lots of comments that deserve answers) >

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/**
 * of_link_property - TODO:
 * dev:
 * con_np:
 * prop:
 *
 * TODO...
 *
 * Any failed attempt to create a link will NOT result in an immediate return.
 * of_link_property() must create all possible links even when one of more
 * attempts to create a link fail.

Why?  isn't one failure enough to prevent probing this device?
Continuing to scan just results in extra work... which will be
repeated every time device_link_check_waiting_consumers() is called

Context:
As I said in the cover letter, avoiding unnecessary probes is just one
of the reasons for this patch. The other (arguably more important)

Agree that it is more important.

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reason for this patch is to make sure suppliers know that they have
consumers that are yet to be probed. That way, suppliers can leave
their resource on AND in the right state if they were left on by the
bootloader. For example, if a clock was left on and at 200 MHz, the
clock provider needs to keep that clock ON and at 200 MHz till all the
consumers are probed.

Answer: Let's say a consumer device Z has suppliers A, B and C. If the
linking fails at A and you return immediately, then B and C could
probe and then figure that they have no more consumers (they don't see
a link to Z) and turn off their resources. And Z could fail
catastrophically.

Then I think that this approach is fatally flawed in the current implementation.

I'm waiting to hear how it is fatally flawed. But maybe this is just a
misunderstanding of the problem?

Fatally flawed because it does not handle modules that add a consumer
device when the module is loaded.

In the text below, I'm not sure if you mixing up two different things
or just that your wording it a bit ambiguous. So pardon my nitpick to
err on the side of clarity.

Please do nitpick.  Clarity is good.

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A device can be added by a module that is loaded.

No, in the example I gave, of_platform_default_populate_init() would
add all 3 of those devices during arch_initcall_sync().

The example you gave does not cover all use cases.

There are modules that add devices when the module is loaded.  You can not
ignore systems using such modules.

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 In that case the device
was not present at late boot when the suppliers may turn off their resources.

In that case, the _drivers_ for those devices aren't present at late
boot. So that they can't request to keep the resources on for their
consumer devices. Since there are no consumer requests on resources,
the suppliers turn off their resources at late boot (since there isn't
a better location as of today). The sync_state() call back added in a
subsequent patche in this series will provide the better location.

And the sync_state() call back will not deal with modules that add consumer
devices when the module is loaded, correct?

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(I am assuming the details since I have not reviewed the patches later in
the series that implement this part.)

Am I missing something?

I think you are mixing up devices getting added/populated with drivers
getting loaded as modules?

Only some modules add devices when they are loaded.  But these modules do
exist.

-Frank

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If I am wrong, then I'll have more comments for your review replies for
patches 2 and 3.

I'll wait for more review replies?

Thanks,
Saravana