Re: [PATCH v4] PCI: Reduce warnings on possible RW1C corruption

[Bjorn Helgaas]

On Fri, Mar 04, 2022 at 01:30:29AM +0000, Chris Packham wrote:
> Hi All,
> 
> On 21/08/20 10:11, Bjorn Helgaas wrote:
> > On Thu, Aug 06, 2020 at 04:14:55PM +1200, Mark Tomlinson 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.
> >>
> >> Suggested-by: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> >> Fixes: fb2659230120 ("PCI: Warn on possible RW1C corruption for sub-32 bit config writes")
> >> Signed-off-by: Mark Tomlinson <mark.tomlinson@xxxxxxxxxxxxxxxxxxx>
> > Applied with collected reviews/acks to pci/enumeration for v5.10,
> > thanks!
> 
> Whatever happened to this change?
> 
> I'm just going through our queue of patches that have been sent upstream 
> and expected this one to be gone after we pulled v5.10. Looking at 
> Linus's tree I don't see it ever having been applied. I couldn't see 
> anything on the relevant mailing lists suggesting that there was a 
> problem with this change so I'm just wondering what's happened to it?

Sorry, I blew it somehow and dropped it.  I applied it again for
v5.18.  Thanks for noticing!

> >> ---
> >> changes in v4:
> >>   - Use bitfield rather than bool to save memory (was meant to be in v3).
> >>
> >>   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..b452467fd133 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 = 1;
> >> +	}
> >>   
> >>   	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..85211a787f8b 100644
> >> --- a/include/linux/pci.h
> >> +++ b/include/linux/pci.h
> >> @@ -626,6 +626,7 @@ struct pci_bus {
> >>   	struct bin_attribute	*legacy_io;	/* Legacy I/O for this bus */
> >>   	struct bin_attribute	*legacy_mem;	/* Legacy mem */
> >>   	unsigned int		is_added:1;
> >> +	unsigned int		unsafe_warn:1;	/* warned about RW1C config write */
> >>   };
> >>   
> >>   #define to_pci_bus(n)	container_of(n, struct pci_bus, dev)
> >> -- 
> >> 2.28.0
> >>