linux-kernel - Re: [PATCH v1] usb: xhci: tegra: Check padctrl interrupt presence in device tree

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Date:   Thu, 21 Oct 2021 20:16:40 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Thierry Reding <treding@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        JC Kuo <jckuo@...dia.com>, Nicolas Chauvet <kwizart@...il.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v1] usb: xhci: tegra: Check padctrl interrupt presence in
 device tree

21.10.2021 20:13, Dmitry Osipenko пишет:
> 21.10.2021 18:20, Alan Stern пишет:
>> On Thu, Oct 21, 2021 at 06:08:41PM +0300, Dmitry Osipenko wrote:
>>> 21.10.2021 17:57, Dmitry Osipenko пишет:
>>>> It might be wrong to disable device_may_wakeup() because it will change
>>>> the system suspend-resume behaviour, i.e. you won't be able to resume by
>>>> USB event, see [1].
>>>>
>>>> [1]
>>>> https://elixir.bootlin.com/linux/v5.15-rc6/source/drivers/usb/host/xhci-tegra.c#L1962
>>>>
>>>> Although, I'm not sure whether this is a correct behaviour to start
>>>> with. Previously, before the offending commit, device_wakeup was never
>>>> enabled for tegra-xusb. Commit message doesn't explain why wakeup is now
>>>> enabled unconditionally, wakeup checks aren't needed at all then. This
>>>> makes no sense, please check it with JC Kuo.
>>>
>>> Although, wakeup could be disabled via sysfs, so it makes sense. Still
>>> it's not clear whether it's a correct behaviour to enable wakeup during
>>> system suspend by default. If it wakes machine from suspend when USB
>>> device is plugged/unplugged, then it's a wrong behaviour.
>>
>> It depends on the details of how the device works.  In most cases we do 
>> want to enable wakeup by default for host controller devices.  The 
>> reason is simple enough: If some USB device attached to the HC is 
>> enabled for wakeup and sends a wakeup request, we don't want the request 
>> to get lost because the HC isn't allowed to forward the request on to 
>> the CPU.
>>
>> But we do not want to enable wakeup for root hubs.  In particular, we 
>> don't want to wake up a suspended system merely because a USB device has 
>> been plugged or unplugged.
>>
>> Clearly this arrangement depends on the hardware making a distinction 
>> between wakeup requests originating from the root hub and those simply 
>> passing through the HC.
> 
> Should USB keyboard be able to wake up every HC or it's a
> machine-specific feature?

I mean whether key press should wake up HC if wake-up is enabled for the
keyboard device.

> I'm asking because wakeup works on a typical
> Intel hardware, but doesn't work on older Tegra SoCs that use Chipidea
> controller. It's not obvious to me whether this is something that
> firmware handles for Intel or it's broken on Tegra. Could you please
> clarify? If it should work for every HC, then I may try to take a closer
> look.
>