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

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Message-ID: <CAMuHMdVqaQ=E43Wrg7GtDD_MGS5ibF9o1DfpDCAq-=F=Exph_Q@mail.gmail.com>
Date: Mon, 10 Nov 2025 10:29:22 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Claudiu Beznea <claudiu.beznea@...on.dev>
Cc: stern@...land.harvard.edu, 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

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...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds