Re: [PATCH v3] PCI: Disallow retraining link for Atheros chips on non-Gen1 PCIe bridges

["Pali Rohár" <pali@kernel.org>]

On Tuesday 11 May 2021 22:39:50 Pali Rohár wrote:
> Hello! I would like to remind this fix. Is there something else needed
> to change?

PING

> On Wednesday 05 May 2021 18:33:57 Pali Rohár wrote:
> > Atheros AR9xxx and QCA9xxx chips have behaviour issues not only after a
> > bus reset, but also after doing retrain link, if PCIe bridge is not in
> > GEN1 mode (at 2.5 GT/s speed):
> > 
> > - QCA9880 and QCA9890 chips throw a Link Down event and completely
> >   disappear from the bus and their config space is not accessible
> >   afterwards.
> > 
> > - QCA9377 chip throws a Link Down event followed by Link Up event, the
> >   config space is accessible and PCI device ID is correct. But trying to
> >   access chip's I/O space causes Uncorrected (Non-Fatal) AER error,
> >   followed by Synchronous external abort 96000210 and Segmentation fault
> >   of insmod while loading ath10k_pci.ko module.
> > 
> > - AR9390 chip throws a Link Down event followed by Link Up event, config
> >   space is accessible, but contains nonsense values. PCI device ID is
> >   0xABCD which indicates HW bug that chip itself was not able to read
> >   values from internal EEPROM/OTP.
> > 
> > - AR9287 chip throws also Link Down and Link Up events, also has
> >   accessible config space containing correct values. But ath9k driver
> >   fails to initialize card from this state as it is unable to access HW
> >   registers. This also indicates that the chip iself is not able to read
> >   values from internal EEPROM/OTP.
> > 
> > These issues related to PCI device ID 0xABCD and to reading internal
> > EEPROM/OTP were previously discussed at ath9k-devel mailing list in
> > following thread:
> > 
> >   https://www.mail-archive.com/ath9k-devel@lists.ath9k.org/msg07529.html
> > 
> > After experiments we've come up with a solution: it seems that Retrain
> > link can be called only when using GEN1 PCIe bridge or when PCIe bridge
> > link speed is forced to 2.5 GT/s. Applying this workaround fixes all
> > mentioned cards.
> > 
> > This issue was reproduced with more cards:
> > - Compex WLE900VX (QCA9880 based / device ID 0x003c)
> > - QCNFA435 (QCA9377 based / device ID 0x0042)
> > - Compex WLE200NX (AR9287 based / device ID 0x002e)
> > - "noname" card (QCA9890 based / device ID 0x003c)
> > - Wistron NKR-DNXAH1 (AR9390 based / device ID 0x0030)
> > on Armada 385 with pci-mvebu.c driver and also on Armada 3720 with
> > pci-aardvark.c driver.
> > 
> > To workaround this issue, this change introduces a new PCI quirk called
> > PCI_DEV_FLAGS_NO_RETRAIN_LINK_WHEN_NOT_GEN1, which is enabled for all
> > Atheros chips with PCI_DEV_FLAGS_NO_BUS_RESET quirk, and also for Atheros
> > chip AR9287.
> > 
> > When this quirk is set, kernel disallows triggering PCI_EXP_LNKCTL_RL
> > bit in config space of PCIe Bridge in the case when PCIe Bridge is
> > capable of higher speed than 2.5 GT/s and this higher speed is already
> > allowed. When PCIe Bridge has accessible LNKCTL2 register, we try to
> > force target link speed to 2.5 GT/s. After this change it is possible
> > to trigger PCI_EXP_LNKCTL_RL bit without issues.
> > 
> > Currently only PCIe ASPM kernel code triggers this PCI_EXP_LNKCTL_RL bit,
> > so quirk check is added only into pcie/aspm.c file.
> > 
> > Signed-off-by: Pali Rohár <pali@kernel.org>
> > Reported-by: Toke Høiland-Jørgensen <toke@redhat.com>
> > Tested-by: Toke Høiland-Jørgensen <toke@redhat.com>
> > Tested-by: Marek Behún <kabel@kernel.org>
> > BugLink: https://lore.kernel.org/linux-pci/87h7l8axqp.fsf@toke.dk/
> > BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=84821
> > BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=192441
> > BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=209833
> > Cc: stable@vger.kernel.org # c80851f6ce63a ("PCI: Add PCI_EXP_LNKCTL2_TLS* macros")
> > 
> > ---
> > Changes since v1:
> > * Move whole quirk code into pcie_downgrade_link_to_gen1() function
> > * Reformat to 80 chars per line where possible
> > * Add quirk also for cards with AR9287 chip (PCI ID 0x002e)
> > * Extend commit message description and add information about 0xABCD
> > 
> > Changes since v2:
> > * Add quirk also for Atheros QCA9377 chip
> > ---
> >  drivers/pci/pcie/aspm.c | 44 +++++++++++++++++++++++++++++++++++++++++
> >  drivers/pci/quirks.c    | 39 ++++++++++++++++++++++++++++--------
> >  include/linux/pci.h     |  2 ++
> >  3 files changed, 77 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> > index ac0557a305af..729b0389562b 100644
> > --- a/drivers/pci/pcie/aspm.c
> > +++ b/drivers/pci/pcie/aspm.c
> > @@ -192,12 +192,56 @@ static void pcie_clkpm_cap_init(struct pcie_link_state *link, int blacklist)
> >  	link->clkpm_disable = blacklist ? 1 : 0;
> >  }
> >  
> > +static int pcie_downgrade_link_to_gen1(struct pci_dev *parent)
> > +{
> > +	u16 reg16;
> > +	u32 reg32;
> > +	int ret;
> > +
> > +	/* Check if link is capable of higher speed than 2.5 GT/s */
> > +	pcie_capability_read_dword(parent, PCI_EXP_LNKCAP, &reg32);
> > +	if ((reg32 & PCI_EXP_LNKCAP_SLS) <= PCI_EXP_LNKCAP_SLS_2_5GB)
> > +		return 0;
> > +
> > +	/* Check if link speed can be downgraded to 2.5 GT/s */
> > +	pcie_capability_read_dword(parent, PCI_EXP_LNKCAP2, &reg32);
> > +	if (!(reg32 & PCI_EXP_LNKCAP2_SLS_2_5GB)) {
> > +		pci_err(parent, "ASPM: Bridge does not support changing Link Speed to 2.5 GT/s\n");
> > +		return -EOPNOTSUPP;
> > +	}
> > +
> > +	/* Force link speed to 2.5 GT/s */
> > +	ret = pcie_capability_clear_and_set_word(parent, PCI_EXP_LNKCTL2,
> > +						 PCI_EXP_LNKCTL2_TLS,
> > +						 PCI_EXP_LNKCTL2_TLS_2_5GT);
> > +	if (!ret) {
> > +		/* Verify that new value was really set */
> > +		pcie_capability_read_word(parent, PCI_EXP_LNKCTL2, &reg16);
> > +		if ((reg16 & PCI_EXP_LNKCTL2_TLS) != PCI_EXP_LNKCTL2_TLS_2_5GT)
> > +			ret = -EINVAL;
> > +	}
> > +
> > +	if (ret) {
> > +		pci_err(parent, "ASPM: Changing Target Link Speed to 2.5 GT/s failed: %d\n", ret);
> > +		return ret;
> > +	}
> > +
> > +	pci_info(parent, "ASPM: Target Link Speed changed to 2.5 GT/s due to quirk\n");
> > +	return 0;
> > +}
> > +
> >  static bool pcie_retrain_link(struct pcie_link_state *link)
> >  {
> >  	struct pci_dev *parent = link->pdev;
> >  	unsigned long end_jiffies;
> >  	u16 reg16;
> >  
> > +	if ((link->downstream->dev_flags & PCI_DEV_FLAGS_NO_RETRAIN_LINK_WHEN_NOT_GEN1) &&
> > +	    pcie_downgrade_link_to_gen1(parent)) {
> > +		pci_err(parent, "ASPM: Retrain Link at higher speed is disallowed by quirk\n");
> > +		return false;
> > +	}
> > +
> >  	pcie_capability_read_word(parent, PCI_EXP_LNKCTL, &reg16);
> >  	reg16 |= PCI_EXP_LNKCTL_RL;
> >  	pcie_capability_write_word(parent, PCI_EXP_LNKCTL, reg16);
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index 653660e3ba9e..4999ad9d08b8 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -3553,23 +3553,46 @@ static void mellanox_check_broken_intx_masking(struct pci_dev *pdev)
> >  DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_MELLANOX, PCI_ANY_ID,
> >  			mellanox_check_broken_intx_masking);
> >  
> > -static void quirk_no_bus_reset(struct pci_dev *dev)
> > +static void quirk_no_bus_reset_and_no_retrain_link(struct pci_dev *dev)
> >  {
> > -	dev->dev_flags |= PCI_DEV_FLAGS_NO_BUS_RESET;
> > +	dev->dev_flags |= PCI_DEV_FLAGS_NO_BUS_RESET |
> > +			  PCI_DEV_FLAGS_NO_RETRAIN_LINK_WHEN_NOT_GEN1;
> >  }
> >  
> >  /*
> > - * Some Atheros AR9xxx and QCA988x chips do not behave after a bus reset.
> > + * Atheros AR9xxx and QCA9xxx chips do not behave after a bus reset and also
> > + * after retrain link when PCIe bridge is not in GEN1 mode at 2.5 GT/s speed.
> >   * The device will throw a Link Down error on AER-capable systems and
> >   * regardless of AER, config space of the device is never accessible again
> >   * and typically causes the system to hang or reset when access is attempted.
> > + * Or if config space is accessible again then it contains only dummy values
> > + * like fixed PCI device ID 0xABCD or values not initialized at all.
> > + * Retrain link can be called only when using GEN1 PCIe bridge or when
> > + * PCIe bridge has forced link speed to 2.5 GT/s via PCI_EXP_LNKCTL2 register.
> > + * To reset these cards it is required to do PCIe Warm Reset via PERST# pin.
> >   * https://lore.kernel.org/r/20140923210318.498dacbd@dualc.maya.org/
> > + * https://lore.kernel.org/r/87h7l8axqp.fsf@toke.dk/
> > + * https://www.mail-archive.com/ath9k-devel@lists.ath9k.org/msg07529.html
> >   */
> > -DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0030, quirk_no_bus_reset);
> > -DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0032, quirk_no_bus_reset);
> > -DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x003c, quirk_no_bus_reset);
> > -DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0033, quirk_no_bus_reset);
> > -DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0034, quirk_no_bus_reset);
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x002e,
> > +			 quirk_no_bus_reset_and_no_retrain_link);
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0030,
> > +			 quirk_no_bus_reset_and_no_retrain_link);
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0032,
> > +			 quirk_no_bus_reset_and_no_retrain_link);
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0033,
> > +			 quirk_no_bus_reset_and_no_retrain_link);
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0034,
> > +			 quirk_no_bus_reset_and_no_retrain_link);
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x003c,
> > +			 quirk_no_bus_reset_and_no_retrain_link);
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0042,
> > +			 quirk_no_bus_reset_and_no_retrain_link);
> > +
> > +static void quirk_no_bus_reset(struct pci_dev *dev)
> > +{
> > +	dev->dev_flags |= PCI_DEV_FLAGS_NO_BUS_RESET;
> > +}
> >  
> >  /*
> >   * Root port on some Cavium CN8xxx chips do not successfully complete a bus
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 86c799c97b77..fdbf7254e4ab 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -227,6 +227,8 @@ enum pci_dev_flags {
> >  	PCI_DEV_FLAGS_NO_FLR_RESET = (__force pci_dev_flags_t) (1 << 10),
> >  	/* Don't use Relaxed Ordering for TLPs directed at this device */
> >  	PCI_DEV_FLAGS_NO_RELAXED_ORDERING = (__force pci_dev_flags_t) (1 << 11),
> > +	/* Don't Retrain Link for device when bridge is not in GEN1 mode */
> > +	PCI_DEV_FLAGS_NO_RETRAIN_LINK_WHEN_NOT_GEN1 = (__force pci_dev_flags_t) (1 << 12),
> >  };
> >  
> >  enum pci_irq_reroute_variant {
> > -- 
> > 2.20.1
> >