linux-kernel - Re: [PATCH v1 1/2] xhci: Add a quirk for full reset on removal

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Message-ID: <CA+zupgwv-LPJJCwkwGUm69xtNTN91qp+gdbYnCdpwNoTNiHF=A@mail.gmail.com>
Date: Thu, 15 May 2025 11:55:55 -0700
From: Roy Luo <royluo@...gle.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: mathias.nyman@...el.com, quic_ugoswami@...cinc.com, 
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] xhci: Add a quirk for full reset on removal

On Thu, May 15, 2025 at 12:33 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Thu, May 15, 2025 at 04:02:07AM +0000, Roy Luo wrote:
> > Commit 6ccb83d6c497 ("usb: xhci: Implement xhci_handshake_check_state()
> > helper") introduced an optimization to xhci_reset() during xhci removal,
> > allowing it to bail out early without waiting for the reset to complete.
> >
> > This behavior can cause issues on SNPS DWC3 USB controller with dual-role
> > capability. When the DWC3 controller exits host mode and removes xhci
> > while a reset is still in progress, and then tries to configure its
> > hardware for device mode, the ongoing reset leads to register access
> > issues; specifically, all register reads returns 0. These issues extend
> > beyond the xhci register space (which is expected during a reset) and
> > affect the entire DWC3 IP block, causing the DWC3 device mode to
> > malfunction.
> >
> > To address this, introduce the `XHCI_FULL_RESET_ON_REMOVE` quirk. When this
> > quirk is set, xhci_reset() always completes its reset handshake, ensuring
> > the controller is in a fully reset state before proceeding.
> >
> > Fixes: 6ccb83d6c497 ("usb: xhci: Implement xhci_handshake_check_state() helper")
> > Signed-off-by: Roy Luo <royluo@...gle.com>
> > ---
> >  drivers/usb/host/xhci-plat.c | 3 +++
> >  drivers/usb/host/xhci.c      | 8 +++++++-
> >  drivers/usb/host/xhci.h      | 1 +
> >  3 files changed, 11 insertions(+), 1 deletion(-)
>
> For some reason this is not "attached" to patch 2 as a series, how did
> you send this?  Did git-send-email not work properly for you?
>
> thanks,
>
> greg k-h

I didn't send them in one batch so the reference message ID is missing
in the second patch.
I've corrected it in v2, sorry for the inconvenience.

Thanks,
Roy