Re: [PATCH V5 1/5] PCI: Add TLP Processing Hints (TPH) support

Lukas Wunner
2024-09-23T07:54:38Z

On Mon, Sep 16, 2024 at 03:50:59PM -0500, Wei Huang wrote:
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1813,6 +1813,7 @@ int pci_save_state(struct pci_dev *dev)
> pci_save_dpc_state(dev);
> pci_save_aer_state(dev);
> pci_save_ptm_state(dev);
> + pci_save_tph_state(dev);
> return pci_save_vc_state(dev);
> }
> EXPORT_SYMBOL(pci_save_state);
> @@ -1917,6 +1918,7 @@ void pci_restore_state(struct pci_dev *dev)
> pci_restore_vc_state(dev);
> pci_restore_rebar_state(dev);
> pci_restore_dpc_state(dev);
> + pci_restore_tph_state(dev);
> pci_restore_ptm_state(dev);
>
> pci_aer_clear_status(dev);

I'm wondering if there's a reason to use a different order on save versus
restore? E.g. does PTM need to be restored last?

> --- a/drivers/pci/pcie/Kconfig
> +++ b/drivers/pci/pcie/Kconfig
> @@ -155,3 +155,14 @@ config PCIE_EDR
> the PCI Firmware Specification r3.2. Enable this if you want to
> support hybrid DPC model which uses both firmware and OS to
> implement DPC.
> +
> +config PCIE_TPH
> + bool "TLP Processing Hints"
> + depends on ACPI

TPH isn't really an ACPI-specific feature, it could exist on
devicetree-based platforms as well. I think there could be valid
use cases for enabling TPH support on such platforms:

E.g. the platform firmware or bootloader might set up the TPH Extended
Capability in a specific way and the kernel would have to save/restore
it on system sleep.

So I'd recommend removing this dependency.

Note that there's a static inline for acpi_check_dsm() which returns
false if CONFIG_ACPI=n, so tph_invoke_dsm() returns AE_ERROR and
pcie_tph_get_cpu_st() returns -EINVAL. It thus looks like you may not
even need an #ifdef.

> diff --git a/drivers/pci/pcie/tph.c b/drivers/pci/pcie/tph.c
> new file mode 100644

The PCIe features added most recently (such as DOE) have been placed
directly in drivers/pci/ instead of the pcie/ subdirectory.
The pcie/ subdirectory mostly deals with port drivers.
So perhaps tph.c should likewise be placed in drivers/pci/ ?

> --- /dev/null
> +++ b/drivers/pci/pcie/tph.c
> @@ -0,0 +1,199 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * TPH (TLP Processing Hints) support
> + *
> + * Copyright (C) 2024 Advanced Micro Devices, Inc.
> + * Eric Van Tassell <Eric.VanTassell@amd.com>
> + * Wei Huang <wei.huang2@amd.com>
> + */
> +#include <linux/pci.h>
> +#include <linux/pci-acpi.h>

This patch doesn't seem to use any of the symbols defined in pci-acpi.h,
or did I miss anything? I'd move the inclusion of pci-acpi.h to the patch
that actually uses its symbols.

Thanks,

Lukas