Received-SPF: pass (google.com: domain of linux-kernel+bounces-161189-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
From: David Laight <David.Laight@ACULAB.COM>
To: 'Guenter Roeck' <linux@roeck-us.net>, Alan Stern
	<stern@rowland.harvard.edu>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Gerd Hoffmann
	<kraxel@redhat.com>
Subject: RE: [PATCH v2] usb: ohci: Prevent missed ohci interrupts
Thread-Topic: [PATCH v2] usb: ohci: Prevent missed ohci interrupts
Thread-Index: AQHaloHtuZ6Ib4ELhkipVPWjjF4HNLF8nf2w
Date: Sat, 27 Apr 2024 21:00:48 +0000
Message-ID: <a1b4bac14c6a4334969cc7d671f3a8eb@AcuMS.aculab.com>
References: <20240424195951.3749388-1-linux@roeck-us.net>
In-Reply-To: <20240424195951.3749388-1-linux@roeck-us.net>
Accept-Language: en-GB, en-US
Precedence: bulk
MIME-Version: 1.0
Content-Language: en-US
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

From: Guenter Roeck
> Sent: 24 April 2024 21:00
>=20
> Testing ohci functionality with qemu's pci-ohci emulation often results
> in ohci interface stalls, resulting in hung task timeouts.
>=20
> The problem is caused by lost interrupts between the emulation and the
> Linux kernel code. Additional interrupts raised while the ohci interrupt
> handler in Linux is running and before the handler clears the interrupt
> status are not handled. The fix for a similar problem in ehci suggests
> that the problem is likely caused by edge-triggered MSI interrupts. See
> commit 0b60557230ad ("usb: ehci: Prevent missed ehci interrupts with
> edge-triggered MSI") for details.
>=20
> Ensure that the ohci interrupt code handles all pending interrupts before
> returning to solve the problem.
>=20
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Fixes: 306c54d0edb6 ("usb: hcd: Try MSI interrupts on PCI devices")
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> v2: Only repeat if the interface is still active
>=20
>  drivers/usb/host/ohci-hcd.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>=20
> diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c
> index 4f9982ecfb58..bb6b50b4a356 100644
> --- a/drivers/usb/host/ohci-hcd.c
> +++ b/drivers/usb/host/ohci-hcd.c
> @@ -888,6 +888,7 @@ static irqreturn_t ohci_irq (struct usb_hcd *hcd)
>  =09/* Check for an all 1's result which is a typical consequence
>  =09 * of dead, unclocked, or unplugged (CardBus...) devices
>  =09 */
> +again:
>  =09if (ints =3D=3D ~(u32)0) {
>  =09=09ohci->rh_state =3D OHCI_RH_HALTED;
>  =09=09ohci_dbg (ohci, "device removed!\n");
> @@ -982,6 +983,13 @@ static irqreturn_t ohci_irq (struct usb_hcd *hcd)
>  =09}
>  =09spin_unlock(&ohci->lock);
>=20
> +=09/* repeat until all enabled interrupts are handled */
> +=09if (ohci->rh_state !=3D OHCI_RH_HALTED) {
> +=09=09ints =3D ohci_readl(ohci, &regs->intrstatus);
> +=09=09if (ints & ohci_readl(ohci, &regs->intrenable))

Doesn't the driver know which interrupts are enabled?
So it should be able to avoid doing two (likely) slow io reads?
(PCIe reads are pretty much guaranteed to be high latency.)

=09David

> +=09=09=09goto again;
> +=09}
> +
>  =09return IRQ_HANDLED;
>  }
>=20
> --
> 2.39.2
>=20

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1=
PT, UK
Registration No: 1397386 (Wales)