[PATCH 1/2] usb: xhci: add relaxed timing quirk bit

On 11/22/2017 10:24 AM, Mathias Nyman wrote:

On 22.11.2017 02:07, Adam Wallis wrote:

quoted

On 11/21/2017 3:06 PM, Rob Herring wrote:

[..]

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I like where you are going with this. Are you saying that I could read for a
device property read from firmware (for DTB or ACPI) like DWC3 does for
"snps,hird-threshold"?

Is that for the same thing? If so, drop the vendor prefix and use
that. Otherwise, a separate property should really be something that
is per board rather than per SoC.

I don't think that's exactly the same property, but it's the same idea I would
prefer to go with. That way, an integer can be passed in via the firmware tables.

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If you mean this, where do you recommend I store the
desired IRQ_CONTROL value - in struct xhci_hcd ?

No idea.

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Or by "compatible" strings, did you mean storing hard-coded values in the
of_device_id usb_xhci_of_match[] array? This would still be hard-coding
(which I
would like to avoid) and also would not work for the ACPI case.

ACPI has match tables too?

Yes, you can use DSD in a way that is similar to OF properties

quoted

It would only be hardcoded per compatible which should be per SoC. Do
you need per board/device tuning? If so, use a property.

The reason why I think it should dynamic via firmware tables is that

* It's much less invasive for vendors to update their DT tables if they need to
adjust on a per device/controller/family/etc basis then to adjust a properties
table in xhci-plat
* This would lead to less polluting in xhci-plat code

quoted

Rob
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I will provide an updated proposed patch sometime this week. I also hope to get
some feedback from Mathias to see what he prefers.

We know have at least two hosts/platforms that need custom interrupt moderation
values

How about adding a u32 device property for xhci with the interrupt moderation
interval in
nanoseconds?? And also add a u32 imod_interval variable to struct xhci_hcd?
?
imod_interval can be set to the current default 40000ns (160*250ns) and
overwritten if
device_property_read_u32() returns something else.

XHCI_MTK_HOST could then use whatever preferred device propery interval value,
and we can get rid of using XHCI_MTK_HOST quirk flag when setting up the IMODI
?
-Mathias

This sounds excellent Mathias. Let me put together a patch along these lines.
Thanks for the feedback!

Adam

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-- 
Adam Wallis
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.