Re: [PATCH v2 03/13] PCI/ASPM: Disable ASPM when driver requests it

From: Bjorn Helgaas <helgaas@kernel.org>
To: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>
Cc: linux-pci@vger.kernel.org,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Rob Herring" <robh@kernel.org>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"Lukas Wunner" <lukas@wunner.de>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"Emmanuel Grumbach" <emmanuel.grumbach@intel.com>,
	linux-kernel@vger.kernel.org,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	ath10k@lists.infradead.org, ath11k@lists.infradead.org,
	ath12k@lists.infradead.org, intel-wired-lan@lists.osuosl.org,
	linux-arm-kernel@lists.infradead.org,
	linux-bluetooth@vger.kernel.org,
	linux-mediatek@lists.infradead.org, linux-rdma@vger.kernel.org,
	linux-wireless@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH v2 03/13] PCI/ASPM: Disable ASPM when driver requests it
Date: Wed, 11 Oct 2023 16:22:06 -0500	[thread overview]
Message-ID: <20231011212206.GA1043224@bhelgaas> (raw)
In-Reply-To: <20230918131103.24119-4-ilpo.jarvinen@linux.intel.com>

On Mon, Sep 18, 2023 at 04:10:53PM +0300, Ilpo Järvinen wrote:
> PCI core/ASPM service driver allows controlling ASPM state through
> pci_disable_link_state() and pci_enable_link_state() API. It was
> decided earlier (see the Link below), to not allow ASPM changes when OS
> does not have control over it but only log a warning about the problem
> (commit 2add0ec14c25 ("PCI/ASPM: Warn when driver asks to disable ASPM,
> but we can't do it")). Similarly, if ASPM is not enabled through
> config, ASPM cannot be disabled.
> ...

> +#ifndef CONFIG_PCIEASPM
> +/*
> + * Always disable ASPM when requested, even when CONFIG_PCIEASPM is
> + * not build to avoid drivers adding code to do it on their own
> + * which caused issues when core does not know about the out-of-band
> + * ASPM state changes.
> + */
> +int pci_disable_link_state_locked(struct pci_dev *pdev, int state)
> +{
> +	struct pci_dev *parent = pdev->bus->self;
> +	struct pci_bus *linkbus = pdev->bus;
> +	struct pci_dev *child;
> +	u16 aspm_enabled, linkctl;
> +	int ret;
> +
> +	if (!parent)
> +		return -ENODEV;

P.S. I think this should look the same to the user (same dmesg log and
same taint, if we do that) as the CONFIG_PCIEASPM=y case.

> +	ret = pcie_capability_read_word(parent, PCI_EXP_LNKCTL, &linkctl);
> +	if (ret != PCIBIOS_SUCCESSFUL)
> +		return pcibios_err_to_errno(ret);
> +	aspm_enabled = linkctl & PCI_EXP_LNKCTL_ASPMC;
> +
> +	ret = pcie_capability_read_word(pdev, PCI_EXP_LNKCTL, &linkctl);
> +	if (ret != PCIBIOS_SUCCESSFUL)
> +		return pcibios_err_to_errno(ret);
> +	aspm_enabled |= linkctl & PCI_EXP_LNKCTL_ASPMC;
> +
> +	/* If no states need to be disabled, don't touch LNKCTL */
> +	if (state & aspm_enabled)
> +		return 0;
> +
> +	ret = pcie_capability_clear_word(parent, PCI_EXP_LNKCTL, PCI_EXP_LNKCTL_ASPMC);
> +	if (ret != PCIBIOS_SUCCESSFUL)
> +		return pcibios_err_to_errno(ret);
> +	list_for_each_entry(child, &linkbus->devices, bus_list)
> +		pcie_capability_clear_word(child, PCI_EXP_LNKCTL, PCI_EXP_LNKCTL_ASPMC);

This disables *all* ASPM states, unlike the version when
CONFIG_PCIEASPM is enabled.  I suppose there's a reason, and maybe a
comment could elaborate on it?

When CONFIG_PCIEASPM is not enabled, I don't think we actively
*disable* ASPM in the hardware; we just leave it as-is, so firmware
might have left it enabled.

> +
> +	return 0;
> +}

Conceptually it seems like the LNKCTL updates here should be the same
whether CONFIG_PCIEASPM is enabled or not (subject to the question
above).

When CONFIG_PCIEASPM is enabled, we might need to do more stuff, but
it seems like the core should be the same.

Bjorn

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