linux-kernel - Re: [PATCH V2] PCI/ASPM: Update saved buffers with latest ASPM

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Message-ID: <3ab3281e-0e10-4af5-a7ab-f46d3fd1889f@linux.intel.com>
Date: Wed, 3 Jan 2024 07:37:50 -0800
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: Vidya Sagar <vidyas@...dia.com>, bhelgaas@...gle.com,
 rafael.j.wysocki@...el.com, kai.heng.feng@...onical.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 V2] PCI/ASPM: Update saved buffers with latest ASPM



On 1/3/2024 2:35 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 System.

Recovery System -> 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 with
> 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>
> ---
> V2:
> * Rebased on top of the tree code
> * Addressed Bjorn's review comments
> 
>  drivers/pci/pcie/aspm.c | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 67b13f26ba7c..d247cabb5e4c 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -138,16 +138,36 @@ static int policy_to_clkpm_state(struct pcie_link_state *link)
>  	return 0;
>  }
>  
> +static void pci_save_aspm_state(struct pci_dev *dev)
> +{
> +	int i = 0;

I don't see a need for this variable. You can use index directly.

> +	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];
> +	i++;
> +	pcie_capability_read_word(dev, PCI_EXP_LNKCTL, &cap[i++]);
> +}
> +
>  static void pcie_set_clkpm_nocheck(struct pcie_link_state *link, int enable)
>  {
>  	struct pci_dev *child;
>  	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;
>  }
>  
> @@ -767,6 +787,10 @@ 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_state(parent);
>  }
>  
>  static void pcie_config_aspm_path(struct pcie_link_state *link)

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer