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Subject: Re: [PATCH wireless-drivers 1/2] mt76: mt76x2e: disable pcie_aspm by
 default
To:     Lorenzo Bianconi <lorenzo@kernel.org>
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>
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>
 <20191024230747.GA30614@lore-desk.lan>
From:   Heiner Kallweit <hkallweit1@gmail.com>
Message-ID: <1de75f53-ab28-9951-092c-19a854ef4907@gmail.com>
Date:   Fri, 25 Oct 2019 12:56:05 +0200
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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@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(+)
>>>>>
>>>
>>> [...]
>>>
>>>>> +
>>>>> +	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.

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