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

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Message-ID: <f2cf0041-8da3-4fa6-8fc4-7fbb7706514c@nvidia.com>
Date: Fri, 23 Feb 2024 02:29:13 +0530
From: Vidya Sagar <vidyas@...dia.com>
To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 bhelgaas@...gle.com, macro@...am.me.uk, ajayagarwal@...gle.com,
 ilpo.jarvinen@...ux.intel.com, david.e.box@...ux.intel.com,
 hkallweit1@...il.com, johan+linaro@...nel.org, xueshuai@...ux.alibaba.com
Cc: 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 22-02-2024 23:50, Kuppuswamy Sathyanarayanan wrote:
> External email: Use caution opening links or attachments
>
>
> On 2/22/24 9:44 AM, 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>
>> ---
>> V4:
>> * Rebased on top of pci/aspm branch
>>
>> V3:
>> * Addressed sathyanarayanan.kuppuswamy's review comments
>>
>> V2:
>> * Rebased on top of the tree code
>> * Addressed Bjorn's review comments
>>
>>   drivers/pci/pcie/aspm.c | 28 ++++++++++++++++++++++++++--
>>   3 files changed, 28 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index cfc5b84dc9c9..3db606ba9344 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -1648,7 +1648,7 @@ static int pci_save_pcie_state(struct pci_dev *dev)
>>        pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &cap[i++]);
>>        pcie_capability_read_word(dev, PCI_EXP_SLTCTL2, &cap[i++]);
>>
>> -     pci_save_aspm_state(dev);
>> +     pci_save_aspm_l1ss_state(dev);
>>        pci_save_ltr_state(dev);
>>
>>        return 0;
>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>> index b217e74966eb..9fe78eb8b07d 100644
>> --- a/drivers/pci/pci.h
>> +++ b/drivers/pci/pci.h
>> @@ -95,7 +95,7 @@ void pci_msix_init(struct pci_dev *dev);
>>   bool pci_bridge_d3_possible(struct pci_dev *dev);
>>   void pci_bridge_d3_update(struct pci_dev *dev);
>>   void pci_aspm_get_l1ss(struct pci_dev *pdev);
>> -void pci_save_aspm_state(struct pci_dev *pdev);
>> +void pci_save_aspm_l1ss_state(struct pci_dev *pdev);
> is this rename a review request? It is not clear from the commit log
> why you are doing it?
I rebased my changes on top of pci/aspm branch which got the support for
save/restore of ASPM L1-SubStates registers merged recently. As I see,
the name of the function that saves the L1SS registers is given as
pci_save_aspm_state() instead of pci_save_aspm_l1ss_state(). My original
change already adds a function to save the ASPM state (only L0s and L1)
info from the link control register and I called it pci_save_aspm_state().
I thought it makes sense to use pci_save_aspm_state() for saving the info
of ASPM-L0s/L1 related registers whereas use pci_save_aspm_l1ss_state() to
save the info of ASPM-L1SS.

Thanks,
Vidya Sagar
>
>>   void pci_restore_aspm_state(struct pci_dev *pdev);
>>   void pci_save_ltr_state(struct pci_dev *dev);
>>   void pci_restore_ltr_state(struct pci_dev *dev);
>> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
>> index 7f1d674ff171..a62648dd52bc 100644
>> --- a/drivers/pci/pcie/aspm.c
>> +++ b/drivers/pci/pcie/aspm.c
>> @@ -24,13 +24,29 @@
>>
>>   #include "../pci.h"
>>
>> +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]);
>> +}
>> +
>>   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)
> --
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer
>