linux-kernel - Re: [RESEND PATCH 1/3] usb: dwc3: Don't reinitialize core during host bus-suspend/resume

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Message-ID: <a30be8a0-63ee-da02-f7a2-4958b7ee35bf@codeaurora.org>
Date:   Thu, 11 Jan 2018 14:25:24 +0530
From:   Manu Gautam <mgautam@...eaurora.org>
To:     Felipe Balbi <balbi@...nel.org>, Roger Quadros <rogerq@...com>
Cc:     linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>
Subject: Re: [RESEND PATCH 1/3] usb: dwc3: Don't reinitialize core during host
 bus-suspend/resume

Hi Felipe,


On 1/11/2018 1:44 PM, Felipe Balbi wrote:
> Hi,
>
> Manu Gautam <mgautam@...eaurora.org> writes:
>>> On 27/09/17 14:19, Manu Gautam wrote:
>>>> Driver powers-off PHYs and reinitializes DWC3 core and gadget on
>>>> resume. While this works fine for gadget mode but in host
>>>> mode there is not re-initialization of host stack. Also, resetting
>>>> bus as part of bus_suspend/resume is not correct which could affect
>>>> (or disconnect) connected devices.
>>>> Fix this by not reinitializing core on suspend/resume in host mode
>>>> for HOST only and OTG/drd configurations.
>>>>
>>> All this seems correct but we (TI) were relying on dwc3_core_exit() to be called
>>> during dwc3_suspend() to have the lowest power state for our platforms.
>>>
>>> After this patch, DWC3 controller and PHYs won't be turned off thus
>>> preventing our platform from reaching low power levels.
>>>
>>> So this is a regression for us (TI) in v4.15-rc.
>>>
>>> Felipe, do you agree?
>>>
>>> If yes I can send a patch which fixes the regression
>>> and also makes USB host work after suspend/resume.
>>>
>> I think it will be better to separate runtime_suspend and pm_suspend handling for
>> host mode in dwc3. Powering offf/on PHYs and dwc3_core_exit/init across system
>> suspend-resume should be ok but doing that for runtime suspend-resume is not
>> correct.
> it sure is. It's part of hibernation-while-disconnected programming sequence
>
>> Let me know if that sounds ok, I can provide a patch for same instead of
>> reverting this which affects runtime PM with dwc3 host.
> nope, that would break platforms using hibernation

Please don't mind me asking this if it is very basic, I am probably missing something there
We should be able to distinguish between runtime_pm vs system_suspend/hibernation
and then process accordingly.
In host mode runtime suspend/resume could happen very often with device connected,
and resetting h/w on every runtime_resume might not be desired. And PHYs drivers
can also support runtime_suspend which would be preferred instead of shutting down
phy.


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