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SubjectRe: [PATCH v4] PCI: Workaround wrong flags completions for IDT switch
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Ethan -

On 7/2/2017 9:55 PM, Ethan Zhao wrote:
> James,
>
> On Wed, Jun 28, 2017 at 5:42 AM, James Puthukattukaran
> <james.puthukattukaran@oracle.com> wrote:
>> From: James Puthukattukaran <james.puthukattukaran@oracle.com>
>>
>> The IDT switch incorrectly flags an ACS source violation on a read config
>> request to an end point device on the completion (IDT 89H32H8G3-YC,
>> errata #36) even though the PCI Express spec states that completions are
>> never affected by ACS source violation (PCI Spec 3.1, Section 6.12.1.1).
>>
>> The suggested workaround by IDT is to issue a configuration write to the
>> downstream device before issuing the first config read. This allows the
>> downstream device to capture its bus number, thus avoiding the ACS
>> violation on the completion.
>>
>> The patch does the following -
>>
>> 1. Disable ACS source violation if enabled
>> 2. Wait for config space access to become available by reading vendor id
>> 3. Do a config write to the end point (errata workaround)
>> 4. Enable ACS source validation (if it was enabled to begin with)
>>
>> -v2: move workaround to pci_bus_read_dev_vendor_id() from
>> pci_bus_check_dev()
>> and move enable_acs_sv to drivers/pci/pci.c -- by Yinghai
>> -v3: add bus->self check for root bus and virtual bus for sriov vfs.
>> -v4: only do workaround for IDT switches
>>
>> Signed-off-by: James Puthukattukaran <james.puthukattukaran@oracle.com>
>> Signed-off-by: Yinghai Lu <yinghai@kernel.org>
>>
>> --
>>
>> drivers/pci/pci.c | 33 +++++++++++++++++++++++++++++++++
>> drivers/pci/pci.h | 1 +
>> drivers/pci/probe.c | 38 ++++++++++++++++++++++++++++++++++++--
>> 3 files changed, 70 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index 563901c..a7a2e2b 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -2835,6 +2835,39 @@ static bool pci_acs_flags_enabled(struct pci_dev
>> *pdev, u16 acs_flags)
>> }
>>
>> /**
>> + * pci_std_enable_acs_sv - enable/disable ACS source validation if
>> supported by the switch
>> + * @dev - pcie switch/RP
>> + * @enable - enable (1) or disable (0) source validation
>> + *
>> + * Returns : < 0 on failure
> You didn't define the meaning of 0 and >0, but you check it later against >0,
> Then what does it mean 0 and >0 ?
see below..
>
>> + * previous acs_sv state

It returns the previous acs_sv state (0 or 1).
>> + */
>> +int pci_std_enable_acs_sv(struct pci_dev *dev, bool enable)
>> +{
>> + int pos;
>> + u16 cap;
>> + u16 ctrl;
>> + int retval;
>> +
>> + pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
>> + if (!pos)
>> + return -ENODEV;
>> +
>> + pci_read_config_word(dev, pos + PCI_ACS_CAP, &cap);
>> + pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
>> +
>> + retval = !!(ctrl & cap & PCI_ACS_SV);
> If the device's ACS SV( ACS Source Validation) capability wasn't
> implemented, the return value of this function will still tell us the
> operation of enabling is successful ? though it might be rare case.
If the ACS capability is implemented, then all bits are expected to have
meaning and are valid. If SV is not implemented by the switch, the
control bit for it should return zero (no source validation done). This
is the PCI specification. The onus is on the switch designer to keep it so.

thanks,
James

>> + if (enable)
>> + ctrl |= (cap & PCI_ACS_SV);
>> + else
>> + ctrl &= ~(cap & PCI_ACS_SV);
>> +
>> + pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
>> +
>> + return retval;
>> +}
>> +
>> +/**
>> * pci_acs_enabled - test ACS against required flags for a given device
>> * @pdev: device to test
>> * @acs_flags: required PCI ACS flags
>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>> index f8113e5..3960c2a 100644
>> --- a/drivers/pci/pci.h
>> +++ b/drivers/pci/pci.h
>> @@ -343,6 +343,7 @@ static inline resource_size_t
>> pci_resource_alignment(struct pci_dev *dev,
>> }
>>
>> void pci_enable_acs(struct pci_dev *dev);
>> +int pci_std_enable_acs_sv(struct pci_dev *dev, bool enable);
>>
>> #ifdef CONFIG_PCIE_PTM
>> void pci_ptm_init(struct pci_dev *dev);
>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> index 19c8950..c154a90 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -1763,8 +1763,8 @@ struct pci_dev *pci_alloc_dev(struct pci_bus *bus)
>> }
>> EXPORT_SYMBOL(pci_alloc_dev);
>>
>> -bool pci_bus_read_dev_vendor_id(struct pci_bus *bus, int devfn, u32 *l,
>> - int crs_timeout)
>> +static bool __pci_bus_read_dev_vendor_id(struct pci_bus *bus, int devfn,
>> + u32 *l, int crs_timeout)
>> {
>> int delay = 1;
>>
>> @@ -1801,6 +1801,40 @@ bool pci_bus_read_dev_vendor_id(struct pci_bus *bus,
>> int devfn, u32 *l,
>>
>> return true;
>> }
>> +
>> +bool pci_bus_read_dev_vendor_id(struct pci_bus *bus, int devfn, u32 *l,
>> + int crs_timeout)
>> +{
>> + int found;
>> + int enable = -1;
>> + int idt_workaround = (bus->self && (bus->self->vendor ==
>> PCI_VENDOR_ID_IDT));
>> + /*
>> + * Some IDT switches flag an ACS violation for config reads
>> + * even though the PCI spec allows for it (PCIe 3.1, 6.1.12.1)
>> + * It flags it because the bus number is not properly set in the
>> + * completion. The workaround is to do a dummy write to properly
>> + * latch number once the device is ready for config operations
>> + */
>> +
>> + if (idt_workaround)
>> + enable = pci_std_enable_acs_sv(bus->self, false);
>> +
>> + found = __pci_bus_read_dev_vendor_id(bus, devfn, l, crs_timeout);
>> +
>> + /*
>> + * The fact that we can read the vendor id indicates that the device
>> + * is ready for config operations. Do the write as part of the
>> errata
>> + * workaround.
>> + */
>> + if (idt_workaround) {
>> + if (found)
>> + pci_bus_write_config_word(bus, devfn, PCI_VENDOR_ID,
>> 0);
>> + if (enable > 0)
>> + pci_std_enable_acs_sv(bus->self, enable);
>> + }
>> +
>> + return found;
>> +}
>> EXPORT_SYMBOL(pci_bus_read_dev_vendor_id);
>>

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