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[v2,2/2] PCI: Reduce warnings on possible RW1C corruption

Message ID 20200731033956.6058-2-mark.tomlinson@alliedtelesis.co.nz
State New
Delegated to: Bjorn Helgaas
Headers show
Series [v2,1/2] PCI: iproc: Set affinity mask on MSI interrupts | expand

Commit Message

Mark Tomlinson July 31, 2020, 3:39 a.m. UTC
For hardware that only supports 32-bit writes to PCI there is the
possibility of clearing RW1C (write-one-to-clear) bits. A rate-limited
messages was introduced by fb2659230120, but rate-limiting is not the
best choice here. Some devices may not show the warnings they should if
another device has just produced a bunch of warnings. Also, the number
of messages can be a nuisance on devices which are otherwise working
fine.

This patch changes the ratelimit to a single warning per bus. This
ensures no bus is 'starved' of emitting a warning and also that there
isn't a continuous stream of warnings. It would be preferable to have a
warning per device, but the pci_dev structure is not available here, and
a lookup from devfn would be far too slow.

Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Fixes: fb2659230120 ("PCI: Warn on possible RW1C corruption for sub-32 bit config writes")
Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
---
 drivers/pci/access.c | 9 ++++++---
 include/linux/pci.h  | 1 +
 2 files changed, 7 insertions(+), 3 deletions(-)

Comments

Rob Herring July 31, 2020, 3:32 p.m. UTC | #1
On Thu, Jul 30, 2020 at 9:40 PM Mark Tomlinson
<mark.tomlinson@alliedtelesis.co.nz> wrote:
>
> For hardware that only supports 32-bit writes to PCI there is the
> possibility of clearing RW1C (write-one-to-clear) bits. A rate-limited
> messages was introduced by fb2659230120, but rate-limiting is not the
> best choice here. Some devices may not show the warnings they should if
> another device has just produced a bunch of warnings. Also, the number
> of messages can be a nuisance on devices which are otherwise working
> fine.
>
> This patch changes the ratelimit to a single warning per bus. This
> ensures no bus is 'starved' of emitting a warning and also that there
> isn't a continuous stream of warnings. It would be preferable to have a
> warning per device, but the pci_dev structure is not available here, and
> a lookup from devfn would be far too slow.

If we don't want to just warn when a 8 or 16 bit access occurs (I'm
not sure if 32-bit only accesses is possible or common. Seems like
PCI_COMMAND would always get written?), then a simple way to do this
is just move this out of line and do something like this where the bus
or device is created/registered:

if (bus->ops->write == pci_generic_config_write32)
    warn()

>
> Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
> Fixes: fb2659230120 ("PCI: Warn on possible RW1C corruption for sub-32 bit config writes")
> Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
> ---
>  drivers/pci/access.c | 9 ++++++---
>  include/linux/pci.h  | 1 +
>  2 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index 79c4a2ef269a..ab85cb7df9b6 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -160,9 +160,12 @@ int pci_generic_config_write32(struct pci_bus *bus, unsigned int devfn,
>          * write happen to have any RW1C (write-one-to-clear) bits set, we
>          * just inadvertently cleared something we shouldn't have.
>          */
> -       dev_warn_ratelimited(&bus->dev, "%d-byte config write to %04x:%02x:%02x.%d offset %#x may corrupt adjacent RW1C bits\n",
> -                            size, pci_domain_nr(bus), bus->number,
> -                            PCI_SLOT(devfn), PCI_FUNC(devfn), where);
> +       if (!bus->unsafe_warn) {
> +               dev_warn(&bus->dev, "%d-byte config write to %04x:%02x:%02x.%d offset %#x may corrupt adjacent RW1C bits\n",
> +                        size, pci_domain_nr(bus), bus->number,
> +                        PCI_SLOT(devfn), PCI_FUNC(devfn), where);
> +               bus->unsafe_warn = true;
> +       }
>
>         mask = ~(((1 << (size * 8)) - 1) << ((where & 0x3) * 8));
>         tmp = readl(addr) & mask;
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 34c1c4f45288..5b6ab593ae09 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -613,6 +613,7 @@ struct pci_bus {
>         unsigned char   primary;        /* Number of primary bridge */
>         unsigned char   max_bus_speed;  /* enum pci_bus_speed */
>         unsigned char   cur_bus_speed;  /* enum pci_bus_speed */
> +       bool            unsafe_warn;    /* warned about RW1C config write */

Make this a bitfield next to 'is_added'.

>  #ifdef CONFIG_PCI_DOMAINS_GENERIC
>         int             domain_nr;
>  #endif
> --
> 2.28.0
>
Mark Tomlinson Aug. 3, 2020, 3:42 a.m. UTC | #2
On Fri, 2020-07-31 at 09:32 -0600, Rob Herring wrote:
> 
> If we don't want to just warn when a 8 or 16 bit access occurs (I'm
> not sure if 32-bit only accesses is possible or common. Seems like
> PCI_COMMAND would always get written?), then a simple way to do this
> is just move this out of line and do something like this where the bus
> or device is created/registered:
> 
> if (bus->ops->write == pci_generic_config_write32)
>     warn()
> 
This doesn't work for many of the PCI drivers, since they wrap the call
to pci_generic_config_write32() in their own function.

> > 
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 34c1c4f45288..5b6ab593ae09 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -613,6 +613,7 @@ struct pci_bus {
> >         unsigned char   primary;        /* Number of primary bridge */
> >         unsigned char   max_bus_speed;  /* enum pci_bus_speed */
> >         unsigned char   cur_bus_speed;  /* enum pci_bus_speed */
> > +       bool            unsafe_warn;    /* warned about RW1C config write */
> 
> Make this a bitfield next to 'is_added'.

Will do, thanks.
diff mbox series

Patch

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index 79c4a2ef269a..ab85cb7df9b6 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -160,9 +160,12 @@  int pci_generic_config_write32(struct pci_bus *bus, unsigned int devfn,
 	 * write happen to have any RW1C (write-one-to-clear) bits set, we
 	 * just inadvertently cleared something we shouldn't have.
 	 */
-	dev_warn_ratelimited(&bus->dev, "%d-byte config write to %04x:%02x:%02x.%d offset %#x may corrupt adjacent RW1C bits\n",
-			     size, pci_domain_nr(bus), bus->number,
-			     PCI_SLOT(devfn), PCI_FUNC(devfn), where);
+	if (!bus->unsafe_warn) {
+		dev_warn(&bus->dev, "%d-byte config write to %04x:%02x:%02x.%d offset %#x may corrupt adjacent RW1C bits\n",
+			 size, pci_domain_nr(bus), bus->number,
+			 PCI_SLOT(devfn), PCI_FUNC(devfn), where);
+		bus->unsafe_warn = true;
+	}
 
 	mask = ~(((1 << (size * 8)) - 1) << ((where & 0x3) * 8));
 	tmp = readl(addr) & mask;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 34c1c4f45288..5b6ab593ae09 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -613,6 +613,7 @@  struct pci_bus {
 	unsigned char	primary;	/* Number of primary bridge */
 	unsigned char	max_bus_speed;	/* enum pci_bus_speed */
 	unsigned char	cur_bus_speed;	/* enum pci_bus_speed */
+	bool		unsafe_warn;	/* warned about RW1C config write */
 #ifdef CONFIG_PCI_DOMAINS_GENERIC
 	int		domain_nr;
 #endif