Date:   Fri, 25 Oct 2019 19:35:00 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Felix Fietkau <nbd@....name>,
        Stanislaw Gruszka <sgruszka@...hat.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Network Development <netdev@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Ryder Lee <ryder.lee@...iatek.com>, Roy Luo <royluo@...gle.com>
Subject: Re: [PATCH wireless-drivers 1/2] mt76: mt76x2e: disable pcie_aspm by default

>
> On 25.10.2019 13:46, Lorenzo Bianconi wrote:
> >> On 25.10.2019 01:07, Lorenzo Bianconi wrote:
> >>>> On 24.10.2019 23:54, Lorenzo Bianconi wrote:
> >>>>>> On 24.10.2019 00:23, Lorenzo Bianconi wrote:
> >>>>>>> On same device (e.g. U7612E-H1) PCIE_ASPM causes continuous mcu hangs and
> >>>>>>> instability and so let's disable PCIE_ASPM by default. This patch has
> >>>>>>> been successfully tested on U7612E-H1 mini-pice card
> >>>>>>>
> >>>>>>> Signed-off-by: Felix Fietkau <nbd@....name>
> >>>>>>> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> >>>>>>> ---
> >>>>>>>  drivers/net/wireless/mediatek/mt76/mmio.c     | 47 +++++++++++++++++++
> >>>>>>>  drivers/net/wireless/mediatek/mt76/mt76.h     |  1 +
> >>>>>>>  .../net/wireless/mediatek/mt76/mt76x2/pci.c   |  2 +
> >>>>>>>  3 files changed, 50 insertions(+)
> >>>>>>>
> >>>>>
> >>>>> [...]
> >>>>>
> >>>>>>> +
> >>>>>>> +       if (parent)
> >>>>>>> +               pcie_capability_clear_word(parent, PCI_EXP_LNKCTL,
> >>>>>>> +                                          aspm_conf);
> >>>>>>
> >>>>>> + linux-pci mailing list
> >>>>>
> >>>>> Hi Heiner,
> >>>>>
> >>>>>>
> >>>>>> All this seems to be legacy code copied from e1000e.
> >>>>>> Fiddling with the low-level PCI(e) registers should be left to the
> >>>>>> PCI core. It shouldn't be needed here, a simple call to
> >>>>>> pci_disable_link_state() should be sufficient. Note that this function
> >>>>>> has a return value meanwhile that you can check instead of reading
> >>>>>> back low-level registers.
> >>>>>
> >>>>> ack, I will add it to v2
> >>>>>
> >>>>>> If BIOS forbids that OS changes ASPM settings, then this should be
> >>>>>> respected (like PCI core does). Instead the network chip may provide
> >>>>>> the option to configure whether it activates certain ASPM (sub-)states
> >>>>>> or not. We went through a similar exercise with the r8169 driver,
> >>>>>> you can check how it's done there.
> >>>>>
> >>>>> looking at the vendor sdk (at least in the version I currently have) there are
> >>>>> no particular ASPM configurations, it just optionally disables it writing directly
> >>>>> in pci registers.
> >>>>> Moreover there are multiple drivers that are currently using this approach:
> >>>>> - ath9k in ath_pci_aspm_init()
> >>>>> - tg3 in tg3_chip_reset()
> >>>>> - e1000e in __e1000e_disable_aspm()
> >>>>> - r8169 in rtl_enable_clock_request()/rtl_disable_clock_request()
> >>>>>
> >>>> All these drivers include quite some legacy code. I can mainly speak for r8169:
> >>>> First versions of the driver are almost as old as Linux. And even though I
> >>>> refactored most of the driver still some legacy code for older chip versions
> >>>> (like the two functions you mentioned) is included.
> >>>>
> >>>>> Is disabling the ASPM for the system the only option to make this minipcie
> >>>>> work?
> >>>>>
> >>>>
> >>>> No. What we do in r8169:
> >>>>
> >>>> - call pci_disable_link_state(pdev, PCIE_LINK_STATE_L0S | PCIE_LINK_STATE_L1)
> >>>> - If it returns 0, then ASPM (including the L1 sub-states) is disabled.
> >>>> - If it returns an errno, then disabling ASPM failed (most likely due to
> >>>>   BIOS forbidding ASPM changes - pci_disable_link_state will spit out
> >>>>   a related warning). In this case r8169 configures the chip to not initiate
> >>>>   transitions to L0s/L1 (the other end of the link may still try to enter
> >>>>   ASPM states). See rtl_hw_aspm_clkreq_enable(). That's sufficient
> >>>>   to avoid the ASPM-related problems with certain versions of this chip.
> >>>>   Maybe your HW provides similar functionality.
> >>>
> >>> yep, I looked at rtl_hw_aspm_clkreq_enable. This is more or less what I did but
> >>> unfortunately there is no specific code or documentation I can use for mt76x2e.
> >>> So as last chance I decided to disable ASPM directly (in this way the chip is
> >>> working fine).
> >>> Do you think a kernel parameter to disable ASPM directly would be acceptable?
> >>>
> >> Module parameters are not the preferred approach, even though some maintainers
> >> may consider it acceptable. I think it should be ok if you disable ASPM per
> >> default. Who wants ASPM can enable the individual states via brand-new
> >> sysfs attributes (provided BIOS allows OS to control ASPM).
> >> However changing ASPM settings via direct register writes may cause
> >> inconsistencies between PCI core and actual settings.
> >> I'm not sure whether there's any general best practice how to deal with the
> >> scenario that a device misbehaves with ASPM enabled and OS isn't allowed to
> >> change ASPM settings.
> >> Maybe the PCI guys can advise on these points.
> >
> > Hi Heiner,
> >
> > I reviewed the mtk sdk and it seems mt7662/mt7612/mt7602 series does not
> > have hw pcie ps support (not sure if it just not implemented or so). In my
> > scenario without disabling ASPM the card does not work at all, so I guess we
> > can proceed with current approach and then try to understand if we can do
> > something better. What do you think?
> >
>
> If there's no proper way to deal with the issue, then you may have to go with
> the current approach. Just what you could do is calling pci_disable_link_state()
> first and do the direct register modification limbo only as a fallback if
> function returns an errno or CONFIG_PCIEASPM isn't defined.

Hi Heiner,

ack, will do in v2

>
> It may make sense to change the return value of the pci_disable_link_state
> dummy if CONFIG_PCIEASPM isn't defined: from 0 to e.g. -EOPNOTSUPP
> Then in the driver it wouldn't be needed to check CONFIG_PCIEASPM.
>
> Interestingly in mt76x2/pci.c there's the following:
>
> /* Fix up ASPM configuration */
>
>         /* RG_SSUSB_G1_CDR_BIR_LTR = 0x9 */
>         mt76_rmw_field(dev, 0x15a10, 0x1f << 16, 0x9);
>
>         /* RG_SSUSB_G1_CDR_BIC_LTR = 0xf */
>         mt76_rmw_field(dev, 0x15a0c, 0xf << 28, 0xf);
>
>         /* RG_SSUSB_CDR_BR_PE1D = 0x3 */
>         mt76_rmw_field(dev, 0x15c58, 0x3 << 6, 0x3);
>
> Would be helpful to know what this does and whether it may need to be adjusted.
> At least in your case this fix attempt doesn't seem to be sufficient.

unfortunately not.

Regards,
Lorenzo

>
>
> > @Ryder, Sean: do you have any hint on this topic?
> >
> > Regards,
> > Lorenzo
> >
> >>
> >>> Regards,
> >>> Lorenzo
> >>>
> >> Heiner
> >>
> >>>>
> >>>>> Regards,
> >>>>> Lorenzo
> >>>>>
> >>>> Heiner
> >>>>
> >>>>>>
> >>>>>>> +}
> >>>>>>> +EXPORT_SYMBOL_GPL(mt76_mmio_disable_aspm);
> >>>>>>> +
> >>>>>>>  void mt76_mmio_init(struct mt76_dev *dev, void __iomem *regs)
> >>>>>>>  {
> >>>>>>>         static const struct mt76_bus_ops mt76_mmio_ops = {
> >>>>>>> diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
> >>>>>>> index 570c159515a0..962812b6247d 100644
> >>>>>>> --- a/drivers/net/wireless/mediatek/mt76/mt76.h
> >>>>>>> +++ b/drivers/net/wireless/mediatek/mt76/mt76.h
> >>>>>>> @@ -578,6 +578,7 @@ bool __mt76_poll_msec(struct mt76_dev *dev, u32 offset, u32 mask, u32 val,
> >>>>>>>  #define mt76_poll_msec(dev, ...) __mt76_poll_msec(&((dev)->mt76), __VA_ARGS__)
> >>>>>>>
> >>>>>>>  void mt76_mmio_init(struct mt76_dev *dev, void __iomem *regs);
> >>>>>>> +void mt76_mmio_disable_aspm(struct pci_dev *pdev);
> >>>>>>>
> >>>>>>>  static inline u16 mt76_chip(struct mt76_dev *dev)
> >>>>>>>  {
> >>>>>>> diff --git a/drivers/net/wireless/mediatek/mt76/mt76x2/pci.c b/drivers/net/wireless/mediatek/mt76/mt76x2/pci.c
> >>>>>>> index 73c3104f8858..264bef87e5c7 100644
> >>>>>>> --- a/drivers/net/wireless/mediatek/mt76/mt76x2/pci.c
> >>>>>>> +++ b/drivers/net/wireless/mediatek/mt76/mt76x2/pci.c
> >>>>>>> @@ -81,6 +81,8 @@ mt76pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> >>>>>>>         /* RG_SSUSB_CDR_BR_PE1D = 0x3 */
> >>>>>>>         mt76_rmw_field(dev, 0x15c58, 0x3 << 6, 0x3);
> >>>>>>>
> >>>>>>> +       mt76_mmio_disable_aspm(pdev);
> >>>>>>> +
> >>>>>>>         return 0;
> >>>>>>>
> >>>>>>>  error:
> >>>>>>>
> >>>>>>
> >>>>
> >>
>

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