linux-kernel - Re: [PATCH 2/4] usb: host: ehci-platform: Call reset assert/deassert on suspend/resume

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Message-ID: <74790e58-f1d1-4d7c-9b75-4176af44e1ff@rowland.harvard.edu>
Date: Mon, 10 Nov 2025 09:46:53 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Claudiu Beznea <claudiu.beznea@...on.dev>, gregkh@...uxfoundation.org,
	p.zabel@...gutronix.de, yoshihiro.shimoda.uh@...esas.com,
	prabhakar.mahadev-lad.rj@...renesas.com,
	kuninori.morimoto.gx@...esas.com, geert+renesas@...der.be,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH 2/4] usb: host: ehci-platform: Call reset assert/deassert
 on suspend/resume

On Mon, Nov 10, 2025 at 10:29:22AM +0100, Geert Uytterhoeven wrote:
> Hi Claudiu,
> 
> On Fri, 7 Nov 2025 at 19:42, Claudiu Beznea <claudiu.beznea@...on.dev> wrote:
> > On 11/7/25 10:01, Geert Uytterhoeven wrote:
> > > On Thu, 6 Nov 2025 at 19:56, Claudiu Beznea <claudiu.beznea@...on.dev> wrote:
> > >> On 11/6/25 16:52, Geert Uytterhoeven wrote:
> > >>> On Thu, 6 Nov 2025 at 15:36, Claudiu <claudiu.beznea@...on.dev> wrote:
> > >>>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> > >>>>
> > >>>> The Renesas RZ/G3S SoC supports a power-saving mode in which power to most
> > >>>> of the SoC components is turned off, including the USB blocks. On the
> > >>>> resume path, the reset signal must be de-asserted before applying any
> > >>>> settings to the USB registers. To handle this properly, call
> > >>>> reset_control_assert() and reset_control_deassert() during suspend and
> > >>>> resume, respectively.
> > >>>>
> > >>>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> > >>>
> > >>>> --- a/drivers/usb/host/ehci-platform.c
> > >>>> +++ b/drivers/usb/host/ehci-platform.c
> > >>>> @@ -454,6 +454,17 @@ static int __maybe_unused ehci_platform_suspend(struct device *dev)
> > >>>>         if (pdata->power_suspend)
> > >>>>                 pdata->power_suspend(pdev);
> > >>>>
> > >>>> +       ret = reset_control_assert(priv->rsts);
> > >>>> +       if (ret) {
> > >>>> +               if (pdata->power_on)
> > >>>> +                       pdata->power_on(pdev);
> > >>>> +
> > >>>> +               ehci_resume(hcd, false);
> > >>>> +
> > >>>> +               if (priv->quirk_poll)
> > >>>> +                       quirk_poll_init(priv);
> > >>>
> > >>> I have my doubts about the effectiveness of this "reverse error
> > >>> handling".  If the reset_control_assert() failed, what are the chances
> > >>> that the device will actually work after trying to bring it up again?
> > >>>
> > >>> Same comment for next patch.
> > >>
> > >> I wasn't sure if I should do this revert or not. In my mind, if the reset
> > >> assert fails, the reset signal is still de-asserted.
> > >
> > > Possibly.  Most reset implementations either cannot fail, or can
> > > fail due to a timeout.  What state the device is in in case of the latter is
> > > hard to guess...
> >
> > In theory there are also failures returned by the subsystem code (e.g. if
> > reset is shared and its reference counts don't have the proper values, if
> > not shared and ops->assert is missing).
> >
> > In case of this particular driver and the ochi-platform one, as the resets
> > request is done with devm_reset_control_array_get_optional_shared() the
> > priv->resets is an array and the assert/de-assert is done through
> > reset_control_array_assert()/reset_control_array_deassert() which, in case
> > of failures, reverts the assert/de-assert operations. It is true that the
> > effectiveness of the revert operation is unknown and depends on the HW, but
> > the subsystem ensures it reverts the previous state in case of failure.
> >
> > For the case resets is not an array, it is true, it depends on the reset
> > driver implementation and hardware.
> >
> > Could you please let me know how would you suggest going forward with the
> > implementation for the patches in this series?
> 
> Up to the USB maintainer...

If you don't have any objections, the patches to ehci-platform.c and 
ohci-platform.c are okay with me.

Acked-by: Alan Stern <stern@...land.harvard.edu>

Alan Stern