Re: [PATCH v2 1/5] usb: dwc2: bus suspend/resume for hosts with DWC2_POWER_DOWN_PARAM_NONE

[Doug Anderson]

Hi,

On Mon, Apr 29, 2019 at 11:06 PM Artur Petrosyan
<Arthur.Petrosyan@xxxxxxxxxxxx> wrote:
>
> Hi,
>
> On 4/29/2019 21:34, Doug Anderson wrote:
> > Hi,
> >
> > On Mon, Apr 29, 2019 at 1:43 AM Artur Petrosyan
> > <Arthur.Petrosyan@xxxxxxxxxxxx> wrote:
> >>
> >> Hi,
> >>
> >> On 4/18/2019 04:15, Douglas Anderson 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@xxxxxxxxxxxx>
> >>> ---
> >>> 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=DwIDAg&c=DPL6_X_6JkXFx7AXWqB0tg&r=9hPBFKCJ_nBjJhGVrrlYOeOQjP_HlVzYqrC_D7niMJI&m=MMfe-4lZePyty6F5zfQ54kiYGuJWNulyRat944LkOsc&s=nExFpAPP_0plZfO5LMG1B-mqt1vyCvE35elVcyVgs8Y&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.
> >> What do you mean by doesn't "just work" ? It seem to me that even after
> >> adding this patch you don't get issues fixed.
> >> You mention that you don't get the hotplug events. Please provide dwc2
> >> debug logs and register dumps on this issue.
> >
> > I mean that partial power down in the currently upstream driver
> > doesn't work.  AKA: if I turn on partial power down in the upstream
> > driver then hotplug events break.  I can try to provide some logs.  On
> > what exact version of the code do you want logs?  Just your series?
> > Just my series?  Mainline?  Some attempt at combining both series?  As
> > I said things seem to sorta work with the combined series.  I can try
> > to clarify if that's the series you want me to test with.  ...or I can
> > wait for your next version?
> As I said this patch doesn't fix the issue with hotplug. With this patch
> or without the hotplug behaves as it was. I have tested it on our setup.
>
> Have you debugged your patch? Does it make any difference on your setup
> ? Does it fix the issue with hotplug?

I think we're still not taking on the same page.

My patch makes no attempt to make partial power down mode work.  My
patch attempts to make things work a little better when using
DWC2_POWER_DOWN_PARAM_NONE.  There is no use testing my patch with
partial power down as it shouldn't have any impact there.


> > I am by no means an expert on dwc2, but an assumption made in my patch
> > is that even cores that can't support partial power down can still
> > save some amount of power when hcd_suspend is called.
> Have you tried to debug dwc2 with power_down == DWC2_POWER_DOWN_PARAM_NONE ?
> >
> > Some evidence that this should be possible: looking at mainline Linux
> > and at dwc2_port_suspend(), I see:
> >
> > * It is currently called even when we have DWC2_POWER_DOWN_PARAM_NONE
> Currently (without your and my patches) (looking at mainline Linux) the
> function dwc2_port_suspend() is called anyway because its call is issued
> by the system. But it performs entering to suspend only in case of
> DWC2_POWER_DOWN_PARAM_PARTIAL.
>
> This is not an assumption. What I am pointing out is based on debugging
> and before making assumptions without debugging for me seems not ok.
>
> Currently without your patch and without my patches. In the
> dwc2_port_suspend() it will enter to suspend only in case that
> power_down == DWC2_POWER_DOWN_PARAM_PARTIAL. Because if you look at the
> code more carefully you will see
>
>         if (hsotg->params.power_down != DWC2_POWER_DOWN_PARAM_PARTIAL)
>                 goto skip_power_saving;
>
> This says if power_down is not DWC2_POWER_DOWN_PARAM_PARTIAL then skip
> power saving.
>
> So but after your patch. If power_down is DWC2_POWER_DOWN_PARAM_NONE it
> tries to suspend.

We must be looking at different code.  I'm looking at Linux's tree, AKA:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/dwc2/hcd.c#n3488

I took a mainline kernel ("v5.1-rc7-5-g83a50840e72a") and added
printouts in dwc2_port_suspend() next to where it set HPRT0_SUSP and
PCGCTL_STOPPCLK in dwc2_port_suspend().

[  454.906364] dwc2 ff540000.usb: I'm setting HPRT0_SUSP
[  454.906367] dwc2 ff540000.usb: I'm setting PCGCTL_STOPPCLK

...and just to confirm:

# grep '^power' /sys/kernel/debug/*.usb/params
/sys/kernel/debug/ff540000.usb/params:power_down                    : 0
/sys/kernel/debug/ff580000.usb/params:power_down                    : 0

So I'm really quite convinced that on mainline Linux with
DWC2_POWER_DOWN_PARAM_NONE that dwc2_port_suspend() sets HPRT0_SUSP
and PCGCTL_STOPPCLK.


> > ...I believe that the net effect of my patch ends up doing both those
> > same two things in hcd_suspend.  That is: when power_down is
> > DWC2_POWER_DOWN_PARAM_NONE I believe my patch is really just doing the
> > same thing that dwc2_port_suspend() would do in the same case.  Is
> > that not OK?
> No if your patch is doing the same thing as it was doing before what is
> the purpose of the patch ?

The purpose is to make _dwc2_hcd_suspend() work more correctly in the
case where power_down is DWC2_POWER_DOWN_PARAM_NONE


> My testes show that your patch doesn't fix the issue related partial
> power down.

Right.  I have been trying to say that my patch doesn't do anything at
all for partial power down.  I am simply trying to make
DWC2_POWER_DOWN_PARAM_NONE work more correctly.

I haven't run all the power consumption tests in quite a long time and
I'll try to get it hooked up tomorrow to confirm that my patch really
truly is still needed to help with power consumption.  I did confirm
that at least there are cases where _dwc2_hcd_suspend() is called and
my patch is what sets the important bits.

-Doug