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Date:   Fri, 3 May 2019 08:25:48 +0000
From:   Artur Petrosyan <Arthur.Petrosyan@...opsys.com>
To:     Doug Anderson <dianders@...omium.org>,
        Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Heiko Stübner <heiko@...ech.de>
CC:     Alan Stern <stern@...land.harvard.edu>,
        Alexandru M Stan <amstan@...omium.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        William Wu <william.wu@...k-chips.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Randy Li <ayaka@...lik.info>, Chris <zyw@...k-chips.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Ryan Case <ryandcase@...omium.org>,
        Amelie Delaunay <amelie.delaunay@...com>,
        "Julius Werner" <jwerner@...omium.org>,
        Dinh Nguyen <dinguyen@...nsource.altera.com>,
        Elaine Zhang <zhangqing@...k-chips.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] usb: dwc2: bus suspend/resume for hosts with
 DWC2_POWER_DOWN_PARAM_NONE

On 5/2/2019 03:58, Doug Anderson wrote:
> Hi,
> 
> 
> On Wed, Apr 17, 2019 at 5:15 PM Douglas Anderson <dianders@...omium.org> wrote:
>>
>> This is an attempt to rehash commit 0cf884e819e0 ("usb: dwc2: add bus
>> suspend/resume for dwc2") on ToT.  That commit was reverted in commit
>> b0bb9bb6ce01 ("Revert "usb: dwc2: add bus suspend/resume for dwc2"")
>> because apparently it broke the Altera SOCFPGA.
>>
>> With all the changes that have happened to dwc2 in the meantime, it's
>> possible that the Altera SOCFPGA will just magically work with this
>> change now.  ...and it would be good to get bus suspend/resume
>> implemented.
>>
>> This change is a forward port of one that's been living in the Chrome
>> OS 3.14 kernel tree.
>>
>> Signed-off-by: Douglas Anderson <dianders@...omium.org>
>> ---
>> This patch was last posted at:
>>
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__lkml.kernel.org_r_1446237173-2D15263-2D1-2Dgit-2Dsend-2Demail-2Ddianders-40chromium.org&d=DwIBaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=9hPBFKCJ_nBjJhGVrrlYOeOQjP_HlVzYqrC_D7niMJI&m=7rxT8EFX9mqUDtTL4P7iuzYNsYROe9rxHGCresSKPTg&s=lTaNUA2XIYPat417fkd1A4Zpvb5eyYtTc1H_NIfW8Vw&e=
>>
>> ...and appears to have died the death of silence.  Maybe it could get
>> some bake time in linuxnext if we can't find any proactive testing?
>>
>> I will also freely admit that I don't know tons about the theory
>> behind this patch.  I'm mostly just re-hashing the original commit
>> from Kever that was reverted since:
>> * Turning on partial power down on rk3288 doesn't "just work".  I
>>    don't get hotplug events.  This is despite dwc2 auto-detecting that
>>    we are power optimized.
>> * If we don't do something like this commit we don't get into as low
>>    of a power mode.
> 
> OK, I spent the day digging more into this patch to confirm that it's
> really the right thing to do.  ...and it still seems to be.
> 
> First off: I'm pretty sure the above sentence "If we don't do
> something like this commit we don't get into as low of a power mode."
> is totally wrong.  Luckily it's "after the cut" and not part of the
> commit message.  Specifically I did a bunch of power testing and I
> couldn't find any instance saving power after this patch.
> 
> ...but, then I looked more carefully at all the history of this
> commit.  I ended up at:
> 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__chromium-2Dreview.googlesource.com_c_chromiumos_third-5Fparty_kernel_-2B_306265_&d=DwIBaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=9hPBFKCJ_nBjJhGVrrlYOeOQjP_HlVzYqrC_D7niMJI&m=7rxT8EFX9mqUDtTL4P7iuzYNsYROe9rxHGCresSKPTg&s=LiyyIyaCPmr88nJeI7TCGtoJBFLRWir_reikYtAHHDw&e=
Looking at this code review I see that this patch fixes whatever issues 
you have on Chrome OS 3.14. But your patch has landed on the top of 
latest Kernel version. With the latest version I think you would not 
have the regression issue.
So you are fixing Chrome OS 3.14.

> 
> ...where I said that this fixes a resume speed regression.  More
> details could be found at the linked bug, AKA:
> 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.chromium.org_p_chromium_issues_detail-3Fid-3D548336&d=DwIBaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=9hPBFKCJ_nBjJhGVrrlYOeOQjP_HlVzYqrC_D7niMJI&m=7rxT8EFX9mqUDtTL4P7iuzYNsYROe9rxHGCresSKPTg&s=7gK8ZGX2zZPqC98CDMhqxEY3Acm_TbYa3fpQjWtvexM&e=
> 
> ...but, sadly, I wasn't as verbose as I usually am and didn't describe
> my exact testing setup.  So I tried to reproduce.  ...and I was able
> to.  I tested on an rk3288-veyron-jerry with an empty USB hub plugged
> into the left port (the host port) and my "servo 2" debug board hooked
> up to the right port.  The "power_Resume" test in Chrome OS certainly
> showed a regression in 3.14 when doing a suspend/resume cycle.
> 
> 
> Digging into the logs in 3.14, before this patch I saw this in the logs:
> 
> usb 3-1: reset high-speed USB device number 2 using dwc2
> usb 3-1.7: reset high-speed USB device number 3 using dwc2
> 
> ...after this patch:
> 
> usb 3-1: USB disconnect, device number 2
> usb 3-1.7: USB disconnect, device number 3
> usb 3-1: new high-speed USB device number 4 using dwc2
> usb 3-1: New USB device found, idVendor=1a40, idProduct=0201, bcdDevice= 1.00
> usb 3-1: New USB device strings: Mfr=0, Product=1, SerialNumber=0
> usb 3-1: Product: USB 2.0 Hub [MTT]
> usb 3-1.7: new high-speed USB device number 5 using dwc2
> usb 3-1.7: New USB device found, idVendor=1a40, idProduct=0101, bcdDevice= 1.11
> usb 3-1.7: New USB device strings: Mfr=0, Product=1, SerialNumber=0
> usb 3-1.7: Product: USB 2.0 Hub
> 
> ...so basically my belief is that without this patch we're just sorta
> leaving the device hanging and it get confused on resume.  After this
> patch we behave slightly better.
> 
> I tested on 4.19 and found much the same.  There:
> 
> usb 2-1: reset high-speed USB device number 2 using dwc2
> usb 2-1.7: reset high-speed USB device number 3 using dwc2
> 
> vs.
> 
> usb 2-1.7: USB disconnect, device number 3
> usb 2-1: USB disconnect, device number 2
> usb 2-1: new high-speed USB device number 4 using dwc2
> usb 2-1: New USB device found, idVendor=1a40, idProduct=0201, bcdDevice= 1.00
> usb 2-1: New USB device strings: Mfr=0, Product=1, SerialNumber=0
> usb 2-1: Product: USB 2.0 Hub [MTT]
> usb 2-1.7: new high-speed USB device number 5 using dwc2
> usb 2-1.7: New USB device found, idVendor=1a40, idProduct=0101, bcdDevice= 1.11
> usb 2-1.7: New USB device strings: Mfr=0, Product=1, SerialNumber=0
> usb 2-1.7: Product: USB 2.0 Hub
> 
> 
> On 4.19 I didn't actually notice a the same resume time regression,
> presumably because things are happening more asynchronously there (I
> didn't confirm this).  ...but in any case it seems like the right
> thing to do to actually do the suspend.
> 
> 
> I'll also re-iterate once more that I'm not claiming that my patch
> helps with "partial power down".  It merely makes the "power savings
> disabled" case work more properly.
> 
> 
> I'll also note that my patch is already in Felipe's "testing/next"
> branch which I continue to believe is correct and good.
> 
> -Doug
> 


-- 
Regards,
Artur

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