linux-kernel - Re: [PATCH v4] Subject: PCI: Enable io space 1k granularity for intel cpu root port

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Message-Id: <20240723080403.9764-1-zhoushengqing@ttyinfo.com>
Date: Tue, 23 Jul 2024 08:04:03 +0000
From: Zhou Shengqing <zhoushengqing@...info.com>
To: helgaas@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org,
	lkp@...el.com,
	llvm@...ts.linux.dev,
	oe-kbuild-all@...ts.linux.dev,
	zhoushengqing@...info.com
Subject: Re: [PATCH v4] Subject: PCI: Enable io space 1k granularity for intel cpu root port


> I think this has potential.  Can you include a more complete citation
> for the Intel spec?  Complete name, document number if available,
> revision, section?  Hopefully it's publically available?

Most of intel CPU EDS specs are under NDA. But you can refer to
https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/xeon-e5-v2-datasheet-vol-2.pdf
keyword:"EN1K".

> + /*
> > + * Per intel sever CPU EDS vol2(register) spec,
> > + * Intel Memory Map/Intel VT-d configuration space,
> > + * IIO MISC Control (IIOMISCCTRL_1_5_0_CFG) — Offset 1C0h
> > + * bit 2.
> > + * Enable 1K (EN1K):
> > + * This bit when set, enables 1K granularity for I/O space decode
> > + * in each of the virtual P2P bridges
> > + * corresponding to root ports, and DMI ports.
> > + */
> > + while ((d = pci_get_device(PCI_VENDOR_ID_INTEL, 0x09a2, d))) {
> 
> To be safe, "d" (the [8086:09a2] device) should be on the same bus as
> "dev" (with VMD, I think we get Root Ports *below* the VMD bridge,
> which would be a different bus, and they presumably are not influenced
> by the EN1K bit.

I modified the code as follows, can you help me review it? 

/* Enable 1k I/O space granularity on the intel root port */
static void quirk_intel_rootport_1k_io(struct pci_dev *dev)
{
	struct pci_dev *d = NULL;
	u16 en1k = 0;

	if (!pci_is_pcie(dev) || pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT)
		return;

	/*
	 * Per intel sever CPU (ICX SPR GNR)EDS vol2(register) spec,
	 * Intel Memory Map/Intel VT-d configuration space,
	 * IIO MISC Control (IIOMISCCTRL_1_5_0_CFG) — Offset 1C0h
	 * bit 2.
	 * Enable 1K (EN1K):
	 * This bit when set, enables 1K granularity for I/O space decode 
	 * in each of the virtual P2P bridges
	 * corresponding to root ports, and DMI ports.
	 */
	while ((d = pci_get_device(PCI_VENDOR_ID_INTEL, 0x09a2, d))) {
		if (pci_domain_nr(d->bus) == pci_domain_nr(dev->bus)) {
			pci_read_config_word(d, 0x1c0, &en1k);
			if (en1k & 0x4) {
				pci_info(dev, "1K I/O windows enabled per %s EN1K setting\n", pci_name(d));
				dev->io_window_1k = 1;
			}
		}
	}
}
DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL,	PCI_ANY_ID,	quirk_intel_rootport_1k_io);

If you have a better method, please let me know. If there are no issues, 
I can submit a new patch.