Re: Raphael, I'd like your help upstreaming this VMD power-saving patch, please

[Russell Haley <yumpusamongus@gmail.com>]

On 5/12/25 4:09 PM, Bjorn Helgaas wrote:

>>  static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
>>  {
>>  	struct pci_dev *child = link->downstream, *parent = link->pdev;
>> @@ -866,7 +891,8 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
>>  	}
>>  
>>  	/* Save default state */
>> -	link->aspm_default = link->aspm_enabled;
>> +	link->aspm_default = pci_fixup_vmd_bridge_enable_aspm(parent) ?
>> +		PCIE_LINK_STATE_ASPM_ALL : link->aspm_enabled;
> 
> PCIE_LINK_STATE_ASPM_ALL includes PCIE_LINK_STATE_L1_2, so I think
> this potentially enables L1.2.  The L1.2 configuration depends on
> T_POWER_ON and Common_Mode_Restore_Time, which depend on electrical
> design and are not discoverable by the kernel.  See PCIe r6.0, sec
> 5.5.4:
> 
>   The TPOWER_ON and Common_Mode_Restore_Time fields must be programmed
>   to the appropriate values based on the components and AC coupling
>   capacitors used in the connection linking the two components. The
>   determination of these values is design implementation specific.

Does that apply to VMD?  As far as I know it's not an actual physical
PCIe device.

- Russell