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

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Message-Id: <20240724033829.4724-1-zhoushengqing@ttyinfo.com>
Date: Wed, 24 Jul 2024 03:38:29 +0000
From: Zhou Shengqing <zhoushengqing@...info.com>
To: haifeng.zhao@...ux.intel.com
Cc: helgaas@...nel.org,
	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

> On 7/23/2024 4:04 PM, Zhou Shengqing wrote:
> >> 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".
> > ...
> > 
> > 	while ((d = pci_get_device(PCI_VENDOR_ID_INTEL, 0x09a2, d))) {
> > 		if (pci_domain_nr(d->bus) == pci_domain_nr(dev->bus)) {
> 
> Perhaps it is enough to check if the 0x09a2 VT-d and the rootport are on the smae bus
> e.g. On my SPR, domain 0000

Thank you for your comment.

Do you mean it shoud be like this?

	while ((d = pci_get_device(PCI_VENDOR_ID_INTEL, 0x09a2, d))) {
		if (d->bus->number == dev->bus->number) {
			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;
			}
		}
	}

> 
> 00:00.0 System peripheral: Intel Corporation Device 09a2 (rev 20)
> 00:0f.0 PCI bridge: Intel Corporation Device 1bbf (rev 10) (prog-if 00 [Normal decode])
> 
>   
> 15:00.0 System peripheral: Intel Corporation Device 09a2 (rev 20)
> 15:01.0 PCI bridge: Intel Corporation Device 352a (rev 04) (prog-if 00 [Normal decode])
> 
> and if you check domain number only, they might sit on different bus, perhaps that
> would make thing complex, could you make sure the VT-d is on the upstream bus of the
> bridge ?

I checked it on ICX SPR EMR GNR, VT-d is always on the same bus with root port,
and VT-d device and function number is always 0. 

Please let me know if further modifications are needed.

> 
> Thanks,
> Ethan