linux-kernel - Re: [PATCH V4] PCI/ASPM: Update saved buffers with latest ASPM

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Message-ID: <8aa0f7c3-0656-4c1b-94c3-cb0d056e84fe@linux.intel.com>
Date: Tue, 5 Mar 2024 14:35:57 -0800
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: Bjorn Helgaas <helgaas@...nel.org>, Vidya Sagar <vidyas@...dia.com>,
 "David E. Box" <david.e.box@...ux.intel.com>
Cc: bhelgaas@...gle.com, macro@...am.me.uk, ajayagarwal@...gle.com,
 ilpo.jarvinen@...ux.intel.com, hkallweit1@...il.com,
 johan+linaro@...nel.org, xueshuai@...ux.alibaba.com,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, treding@...dia.com,
 jonathanh@...dia.com, kthota@...dia.com, mmaddireddy@...dia.com,
 sagar.tv@...il.com
Subject: Re: [PATCH V4] PCI/ASPM: Update saved buffers with latest ASPM


On 3/5/24 2:03 PM, Bjorn Helgaas wrote:
> [+to Sathy, David in case you want to update your Reviewed-by]
>
> On Thu, Feb 22, 2024 at 11:14:36PM +0530, Vidya Sagar wrote:
>> Many PCIe device drivers save the configuration state of their respective
>> devices during probe and restore the same when their 'slot_reset' hook
>> is called through PCIe Error Recovery Handler.
>>
>> If the system has a change in ASPM policy after the driver's probe is
>> called and before error event occurred, 'slot_reset' hook restores the
>> PCIe configuration state to what it was at the time of probe but not to
>> what it was just before the occurrence of the error event.
>> This effectively leads to a mismatch in the ASPM configuration between
>> the device and its upstream parent device.
>>
>> Update the saved configuration state of the device with the latest info
>> whenever there is a change w.r.t ASPM policy.
>>
>> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
>> -void pci_save_aspm_state(struct pci_dev *pdev);
>> +void pci_save_aspm_l1ss_state(struct pci_dev *pdev);
> I rebased this again on top of my pci/aspm updates to remove the need
> for the rename above.
>
>> +static void pci_save_aspm_state(struct pci_dev *dev)
>> +{
>> +	struct pci_cap_saved_state *save_state;
>> +	u16 *cap;
>> +
>> +	if (!pci_is_pcie(dev))
>> +		return;
>> +
>> +	save_state = pci_find_saved_cap(dev, PCI_CAP_ID_EXP);
>> +	if (!save_state)
>> +		return;
>> +
>> +	cap = (u16 *)&save_state->cap.data[0];
>> +	pcie_capability_read_word(dev, PCI_EXP_LNKCTL, &cap[1]);
> And I changed this part so it only updates the PCI_EXP_LNKCTL_ASPMC
> bits, not the entire LNKCTL.
>
> Updating the entire saved register probably wouldn't *break* anything,
> but it could randomly hide other LNKCTL changes depending on whether
> or not ASPM configuration was changed in the interim.  For example:
>
>   - driver .probe() saves LNKCTL
>   - LNKCTL changes some non-ASPMC thing via setpci or other mechanism
>   - save_state updated via pcie_config_aspm_link()
>
> A restore in .slot_reset() would restore different LNKCTL values for
> the non-ASPMC change depending on whether pcie_config_aspm_link() was
> used.
>
> I applied it on pci/aspm for v6.9.  Please take a look and make sure
> it still does what you need:
> https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/commit/?h=aspm&id=a6315434436d587f70e489e6365c5b7e20176a71
>
> Sathy and David, I didn't add your Reviewed-by because I didn't want
> to presume that you were OK with my changes.  But I'd be more than
> happy to add them if you take a look.

Your update looks fine to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

>
> Bjorn
>
>> +}
>> +
>>  void pci_aspm_get_l1ss(struct pci_dev *pdev)
>>  {
>>  	/* Read L1 PM substate capabilities */
>>  	pdev->l1ss = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_L1SS);
>>  }
>>  
>> -void pci_save_aspm_state(struct pci_dev *pdev)
>> +void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
>>  {
>>  	struct pci_cap_saved_state *save_state;
>>  	u16 l1ss = pdev->l1ss;
>> @@ -309,10 +325,12 @@ static void pcie_set_clkpm_nocheck(struct pcie_link_state *link, int enable)
>>  	struct pci_bus *linkbus = link->pdev->subordinate;
>>  	u32 val = enable ? PCI_EXP_LNKCTL_CLKREQ_EN : 0;
>>  
>> -	list_for_each_entry(child, &linkbus->devices, bus_list)
>> +	list_for_each_entry(child, &linkbus->devices, bus_list) {
>>  		pcie_capability_clear_and_set_word(child, PCI_EXP_LNKCTL,
>>  						   PCI_EXP_LNKCTL_CLKREQ_EN,
>>  						   val);
>> +		pci_save_aspm_state(child);
>> +	}
>>  	link->clkpm_enabled = !!enable;
>>  }
>>  
>> @@ -931,6 +949,12 @@ static void pcie_config_aspm_link(struct pcie_link_state *link, u32 state)
>>  		pcie_config_aspm_dev(parent, upstream);
>>  
>>  	link->aspm_enabled = state;
>> +
>> +	/* Update latest ASPM configuration in saved context */
>> +	pci_save_aspm_state(link->downstream);
>> +	pci_save_aspm_l1ss_state(link->downstream);
>> +	pci_save_aspm_state(parent);
>> +	pci_save_aspm_l1ss_state(parent);
>>  }
>>  
>>  static void pcie_config_aspm_path(struct pcie_link_state *link)
>> -- 
>> 2.25.1
>>
-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer