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Date:   Fri, 25 Oct 2019 01:07:47 +0200
From:   Lorenzo Bianconi <lorenzo@kernel.org>
To:     Heiner Kallweit <hkallweit1@gmail.com>
Cc:     kvalo@codeaurora.org, linux-wireless@vger.kernel.org, nbd@nbd.name,
        sgruszka@redhat.com, lorenzo.bianconi@redhat.com,
        oleksandr@natalenko.name, netdev@vger.kernel.org,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>
Subject: Re: [PATCH wireless-drivers 1/2] mt76: mt76x2e: disable pcie_aspm by
 default
Message-ID: <20191024230747.GA30614@lore-desk.lan>
References: <cover.1571868221.git.lorenzo@kernel.org>
 <fec60f066bab1936d58b2e69bae3f20e645d1304.1571868221.git.lorenzo@kernel.org>
 <5924c8eb-7269-b8ef-ad0e-957104645638@gmail.com>
 <20191024215451.GA30822@lore-desk.lan>
 <9cac34a5-0bfe-0443-503f-218210dab4d6@gmail.com>
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> 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@nbd.name>
> >>> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.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(+)
> >>>
> >=20
> > [...]
> >=20
> >>> +
> >>> +	if (parent)
> >>> +		pcie_capability_clear_word(parent, PCI_EXP_LNKCTL,
> >>> +					   aspm_conf);
> >>
> >> + linux-pci mailing list
> >=20
> > Hi Heiner,
> >=20
> >>
> >> 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.
> >=20
> > ack, I will add it to v2
> >=20
> >> 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.
> >=20
> > looking at the vendor sdk (at least in the version I currently have) th=
ere are
> > no particular ASPM configurations, it just optionally disables it writi=
ng directly
> > in pci registers.
> > Moreover there are multiple drivers that are currently using this appro=
ach:
> > - 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()
> >=20
> 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 versi=
ons
> (like the two functions you mentioned) is included.
>=20
> > Is disabling the ASPM for the system the only option to make this minip=
cie
> > work?
> >=20
>=20
> No. What we do in r8169:
>=20
> - 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 initi=
ate
>   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 mt76=
x2e.
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 acceptabl=
e?

Regards,
Lorenzo

>=20
> > Regards,
> > Lorenzo
> >=20
> Heiner
>=20
> >>
> >>> +}
> >>> +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 =3D {
> >>> 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 o=
ffset, u32 mask, u32 val,
> >>>  #define mt76_poll_msec(dev, ...) __mt76_poll_msec(&((dev)->mt76), __=
VA_ARGS__)
> >>> =20
> >>>  void mt76_mmio_init(struct mt76_dev *dev, void __iomem *regs);
> >>> +void mt76_mmio_disable_aspm(struct pci_dev *pdev);
> >>> =20
> >>>  static inline u16 mt76_chip(struct mt76_dev *dev)
> >>>  {
> >>> diff --git a/drivers/net/wireless/mediatek/mt76/mt76x2/pci.c b/driver=
s/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 pc=
i_device_id *id)
> >>>  	/* RG_SSUSB_CDR_BR_PE1D =3D 0x3 */
> >>>  	mt76_rmw_field(dev, 0x15c58, 0x3 << 6, 0x3);
> >>> =20
> >>> +	mt76_mmio_disable_aspm(pdev);
> >>> +
> >>>  	return 0;
> >>> =20
> >>>  error:
> >>>
> >>
>=20

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