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

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Message-ID: <2912551a-b4c6-4bd4-8c1c-22de7fd8fa20@linux.intel.com>
Date: Wed, 24 Jul 2024 15:51:18 +0800
From: Ethan Zhao <haifeng.zhao@...ux.intel.com>
To: Zhou Shengqing <zhoushengqing@...info.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
Subject: Re: [PATCH v4] PCI: Enable io space 1k granularity for intel cpu root
 port

On 7/24/2024 2:35 PM, Zhou Shengqing wrote:
>>> 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.
>> Yes, every VT-d instance in the root complex and the root port integrated are
>> on the same bus. and VT-d is the first device of that bus.
>>
>> The EDS doesn't say if there is exception one of the VT-d instances in an
>> system its EN1K wasn't set while others were set, vice vesa. so I suggest
>> just check the VT-d and then set the root port's io_windows_1k of the same bus.
> But as Bjorn mentioned at July 12, 2024, 6:48 p.m.,
>
> "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."
>
> When VMD enabled, just check bus number identical may lead to enable
> 1k io windows for VMD domain root port. E.g. 0000:80:00.0 is a
> VT-d(09a2). If VMD enabled, there might be a root port 10000:80:01.0 present.
> this code may lead to enable 10000:80:01.0 io_window_1k = 1.
> This is probably not expected.
>
> If I modify it like this,
>
> 	while ((d = pci_get_device(PCI_VENDOR_ID_INTEL, 0x09a2, d))) {

BTW, don't save letters to use single letter variable 'd', please use 'vtd_dev' or
something else to express the VT-d device.

> 	---if (d->bus->number == dev->bus->number) {
> 	+++if (d->bus == dev->bus) {

What if their 'bus' are NULL, though it is almost impossible. :)

> 			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;
> 			}
> 		}
> 	}
>      
> Can the situation mentioned above be avoided?

Yes, my understanding, as Bjorn pointed out root port extended from VMD
bridge not on the same bus as VT-d.



Thanks,
Ethan

>
> Hope for your suggestion.
>
>> Hope that works for your case.
>>