Re: [PATCH V8 RESEND 4/4] PCI: vmd: Add quirk to configure PCIe ASPM and LTR

[Sathyanarayanan Kuppuswamy]

HI,

On 11/18/22 6:14 PM, David E. Box wrote:
> PCIe ports reserved for VMD use are not visible to BIOS and therefore not
> configured to enable PCIe ASPM or LTR values (which BIOS will configure if
> they are not set). Lack of this programming results in high power
> consumption on laptops as reported in bugzilla.  For affected products use
> pci_enable_link_state to set the allowed link states for devices on the
> root ports. Also set the LTR value to the maximum value needed for the SoC.
> 
> This is a workaround for products from Rocket Lake through Alder Lake.
> Raptor Lake, the latest product at this time, has already implemented LTR
> configuring in BIOS. Future products will move ASPM configuration back to
> BIOS as well.  As this solution is intended for laptops, support is not
> added for hotplug or for devices downstream of a switch on the root port.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=212355
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=215063
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=213717
> 
> Signed-off-by: Michael Bottini <michael.a.bottini@xxxxxxxxxxxxxxx>
> Signed-off-by: David E. Box <david.e.box@xxxxxxxxxxxxxxx>
> Reviewed-by: Jon Derrick <jonathan.derrick@xxxxxxxxx>
> Reviewed-by: Nirmal Patel <nirmal.patel@xxxxxxxxxxxxxxx>
> ---
>  V8
>   - Removed struct vmd_device_data patch. Instead use #define for the LTR
>     value which is the same across all products needing the quirk.
>  V7
>   - No change
>  V6
>   - Set ASPM first before setting LTR. This is needed because some
>     devices may only have LTR set by BIOS and not ASPM
>   - Skip setting the LTR if the current LTR in non-zero.
>  V5
>   - Provide the LTR value as driver data.
>   - Use DWORD for the config space write to avoid PCI WORD access bug.
>   - Set ASPM links firsts, enabling all link states, before setting a
>     default LTR if the capability is present
>   - Add kernel message that VMD is setting the device LTR.
>  V4
>   - Refactor vmd_enable_apsm() to exit early, making the lines shorter
>     and more readable. Suggested by Christoph.
>  V3
>   - No changes
>  V2
>   - Use return status to print pci_info message if ASPM cannot be enabled.
>   - Add missing static declaration, caught by lkp@xxxxxxxxx
> 
>  drivers/pci/controller/vmd.c | 64 ++++++++++++++++++++++++++++++++----
>  1 file changed, 58 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index 86f3085db014..cba57e3091f6 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -66,12 +66,22 @@ enum vmd_features {
>  	 * interrupt handling.
>  	 */
>  	VMD_FEAT_CAN_BYPASS_MSI_REMAP		= (1 << 4),
> +
> +	/*
> +	 * Enable ASPM on the PCIE root ports and set the default LTR of the
> +	 * storage devices on platforms where these values are not configured by
> +	 * BIOS. This is needed for laptops, which require these settings for
> +	 * proper power management of the SoC.
> +	 */
> +	VMD_FEAT_BIOS_PM_QUIRK		= (1 << 5),
>  };
>  
>  #define VMD_FEATS_CLIENT	(VMD_FEAT_HAS_MEMBAR_SHADOW_VSCAP |	\
>  				 VMD_FEAT_HAS_BUS_RESTRICTIONS |	\
>  				 VMD_FEAT_OFFSET_FIRST_VECTOR)
>  
> +#define VMD_BIOS_PM_QUIRK_LTR	0x1003	/* 3145728 ns */
> +
>  static DEFINE_IDA(vmd_instance_ida);
>  
>  /*
> @@ -713,6 +723,46 @@ static void vmd_copy_host_bridge_flags(struct pci_host_bridge *root_bridge,
>  	vmd_bridge->native_dpc = root_bridge->native_dpc;
>  }
>  
> +/*
> + * Enable ASPM and LTR settings on devices that aren't configured by BIOS.
> + */
> +static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
> +{
> +	unsigned long features = *(unsigned long *)userdata;
> +	u16 ltr = VMD_BIOS_PM_QUIRK_LTR;
> +	u32 ltr_reg;
> +	int pos;
> +
> +	if (!(features & VMD_FEAT_BIOS_PM_QUIRK))
> +		return 0;
> +
> +	pci_enable_link_state(pdev, PCIE_LINK_STATE_ALL);
> +
> +	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_LTR);
> +	if (!pos)
> +		return 0;
> +
> +	/*
> +	 * Skip if the max snoop LTR is non-zero, indicating BIOS has set it
> +	 * so the LTR quirk is not needed.
> +	 */
> +	pci_read_config_dword(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, &ltr_reg);
> +	if (!!(ltr_reg & (PCI_LTR_VALUE_MASK | PCI_LTR_SCALE_MASK)))
> +		return 0;
> +
> +	/*
> +	 * Set the default values to the maximum required by the platform to
> +	 * allow the deepest power management savings. Write as a DWORD where
> +	 * the lower word is the max snoop latency and the upper word is the
> +	 * max non-snoop latency.
> +	 */
> +	ltr_reg = (ltr << 16) | ltr;
> +	pci_write_config_dword(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, ltr_reg);
> +	pci_info(pdev, "VMD: Default LTR value set by driver\n");
> +
> +	return 0;
> +}
> +
>  static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>  {
>  	struct pci_sysdata *sd = &vmd->sysdata;
> @@ -867,6 +917,8 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>  		pci_reset_bus(child->self);
>  	pci_assign_unassigned_bus_resources(vmd->bus);
>  
> +	pci_walk_bus(vmd->bus, vmd_pm_enable_quirk, &features);
> +
>  	/*
>  	 * VMD root buses are virtual and don't return true on pci_is_pcie()
>  	 * and will fail pcie_bus_configure_settings() early. It can instead be
> @@ -1005,17 +1057,17 @@ static const struct pci_device_id vmd_ids[] = {
>  				VMD_FEAT_HAS_BUS_RESTRICTIONS |
>  				VMD_FEAT_CAN_BYPASS_MSI_REMAP,},
>  	{PCI_VDEVICE(INTEL, 0x467f),
> -		.driver_data = VMD_FEATS_CLIENT,},
> +		.driver_data = VMD_FEATS_CLIENT | VMD_FEAT_BIOS_PM_QUIRK,},
>  	{PCI_VDEVICE(INTEL, 0x4c3d),
> -		.driver_data = VMD_FEATS_CLIENT,},
> +		.driver_data = VMD_FEATS_CLIENT | VMD_FEAT_BIOS_PM_QUIRK,},
>  	{PCI_VDEVICE(INTEL, 0xa77f),
> -		.driver_data = VMD_FEATS_CLIENT,},
> +		.driver_data = VMD_FEATS_CLIENT | VMD_FEAT_BIOS_PM_QUIRK,},
>  	{PCI_VDEVICE(INTEL, 0x7d0b),
> -		.driver_data = VMD_FEATS_CLIENT,},
> +		.driver_data = VMD_FEATS_CLIENT | VMD_FEAT_BIOS_PM_QUIRK,},
>  	{PCI_VDEVICE(INTEL, 0xad0b),
> -		.driver_data = VMD_FEATS_CLIENT,},
> +		.driver_data = VMD_FEATS_CLIENT | VMD_FEAT_BIOS_PM_QUIRK,},
>  	{PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_VMD_9A0B),
> -		.driver_data = VMD_FEATS_CLIENT,},
> +		.driver_data = VMD_FEATS_CLIENT | VMD_FEAT_BIOS_PM_QUIRK,},

Why not add VMD_FEAT_BIOS_PM_QUIRK part of VMD_FEATS_CLIENT?

>  	{0,}
>  };
>  MODULE_DEVICE_TABLE(pci, vmd_ids);

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer