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Message-ID: <24ec3f1f-b39c-eeb1-d53-ed97e2ccdb4f@linux.intel.com>
Date: Wed, 21 Sep 2022 16:20:50 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: unlisted-recipients:; (no To-header on input)
cc: Lennert Buytenhek <buytenh@...tstofly.org>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jirislaby@...nel.org>,
Alex Williamson <alex.williamson@...com>,
Aristeu Sergio Rozanski Filho <aris@...hedrallabs.org>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-serial <linux-serial@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Lennert Buytenhek <buytenh@...sta.com>
Subject: Re: [PATCH v3 1/1] serial: 8250: Toggle IER bits on only after irq
has been set up
On Mon, 19 Sep 2022, Ilpo Järvinen wrote:
> Invoking TIOCVHANGUP on 8250_mid port on Ice Lake-D and then reopening
> the port triggers these faults during serial8250_do_startup():
>
> DMAR: DRHD: handling fault status reg 3
> DMAR: [DMA Write NO_PASID] Request device [00:1a.0] fault addr 0x0 [fault reason 0x05] PTE Write access is not set
>
> If the IRQ hasn't been set up yet, the UART will have zeroes in its MSI
> address/data registers. Disabling the IRQ at the interrupt controller
> won't stop the UART from performing a DMA write to the address programmed
> in its MSI address register (zero) when it wants to signal an interrupt.
>
> The UARTs (in Ice Lake-D) implement PCI 2.1 style MSI without masking
> capability, so there is no way to mask the interrupt at the source PCI
> function level, except disabling the MSI capability entirely, but that
> would cause it to fall back to INTx# assertion, and the PCI specification
> prohibits disabling the MSI capability as a way to mask a function's
> interrupt service request.
>
> The MSI address register is zeroed during by the hangup as the irq is
> freed. The interrupt is signalled during serial8250_do_startup()
> performing a THRE test that temporarily toggles THRI in IER. The THRE
> test currently occurs before UART's irq (and MSI address) is properly
> set up.
>
> Refactor serial8250_do_startup() such that irq is set up before the
> THRE test. The current irq setup code is intermixed with the timer
> setup code. As THRE test must be performed prior to the timer setup,
> extract it into own function and call it only after the THRE test.
>
> Reported-by: Lennert Buytenhek <buytenh@...sta.com>
> Tested-by: Lennert Buytenhek <buytenh@...sta.com>
> Fixes: 40b36daad0ac ("[PATCH] 8250 UART backup timer")
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
>
> v3:
> - Improved the commit with Lennert's superior descriptions.
> - Added Andy's Rev-by
>
> drivers/tty/serial/8250/8250.h | 2 ++
> drivers/tty/serial/8250/8250_core.c | 16 +++++++++++-----
> drivers/tty/serial/8250/8250_port.c | 8 +++++---
> 3 files changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> index 287153d32536..dbf4c1204bf3 100644
> --- a/drivers/tty/serial/8250/8250.h
> +++ b/drivers/tty/serial/8250/8250.h
> @@ -403,3 +403,5 @@ static inline int serial_index(struct uart_port *port)
> {
> return port->minor - 64;
> }
> +
> +void univ8250_setup_timer(struct uart_8250_port *up);
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 2e83e7367441..10d535640434 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -298,10 +298,9 @@ static void serial8250_backup_timeout(struct timer_list *t)
> jiffies + uart_poll_timeout(&up->port) + HZ / 5);
> }
>
> -static int univ8250_setup_irq(struct uart_8250_port *up)
> +void univ8250_setup_timer(struct uart_8250_port *up)
> {
> struct uart_port *port = &up->port;
> - int retval = 0;
>
> /*
> * The above check will only give an accurate result the first time
> @@ -322,10 +321,17 @@ static int univ8250_setup_irq(struct uart_8250_port *up)
> */
> if (!port->irq)
> mod_timer(&up->timer, jiffies + uart_poll_timeout(port));
> - else
> - retval = serial_link_irq_chain(up);
> +}
> +EXPORT_SYMBOL_GPL(univ8250_setup_timer);
>
> - return retval;
> +static int univ8250_setup_irq(struct uart_8250_port *up)
> +{
> + struct uart_port *port = &up->port;
> +
> + if (port->irq)
> + return serial_link_irq_chain(up);
> +
> + return 0;
> }
>
> static void univ8250_release_irq(struct uart_8250_port *up)
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 39b35a61958c..6e8e16227a3a 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -2294,6 +2294,10 @@ int serial8250_do_startup(struct uart_port *port)
> if (port->irq && (up->port.flags & UPF_SHARE_IRQ))
> up->port.irqflags |= IRQF_SHARED;
>
> + retval = up->ops->setup_irq(up);
> + if (retval)
> + goto out;
> +
> if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
> unsigned char iir1;
>
> @@ -2336,9 +2340,7 @@ int serial8250_do_startup(struct uart_port *port)
> }
> }
>
> - retval = up->ops->setup_irq(up);
> - if (retval)
> - goto out;
> + univ8250_setup_timer(up);
>
> /*
> * Now, initialize the UART
Hi Greg,
Please scratch this patch. It seems to create a circular dependency issue
with allmodconfig. I'll send v4 once the problem is sorted out.
--
i.
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