Subject: Re: [PATCH wireless-drivers 1/2] mt76: mt76x2e: disable pcie_aspm by default

From: Lorenzo Bianconi <[email-masked]>
Date: Fri, 25 Oct 2019 01:07:47 +0200

> 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 <[email-masked]>
> >>> Signed-off-by: Lorenzo Bianconi <[email-masked]>
> >>> ---
> >>>  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?

Regards,
Lorenzo

> 
> > 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:
> >>>
> >>
>