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From: "Jiahui Cen" <cenjiahui@huawei.com>
To: <devel@edk2.groups.io>, <lersek@redhat.com>,
	"Ni, Ray" <ray.ni@intel.com>
Cc: "Justen, Jordan L" <jordan.l.justen@intel.com>,
	"ard.biesheuvel@arm.com" <ard.biesheuvel@arm.com>,
	"leif@nuviainc.com" <leif@nuviainc.com>,
	"xieyingtai@huawei.com" <xieyingtai@huawei.com>,
	"miaoyubo@huawei.com" <miaoyubo@huawei.com>,
	"xuxiaoyang2@huawei.com" <xuxiaoyang2@huawei.com>,
	Alex Williamson <alex.williamson@redhat.com>
Subject: Re: [edk2-devel] [PATCH v2 0/4] Add extra pci roots support for Arm
Date: Thu, 17 Dec 2020 21:52:17 +0800	[thread overview]
Message-ID: <e32b0311-d47b-c7f9-58f4-eb3aa9beb92b@huawei.com> (raw)
In-Reply-To: <ec6c1550-f1cf-2742-2914-58b4a939e62a@redhat.com>



On 2020/12/17 21:23, Laszlo Ersek wrote:
> On 12/15/20 13:52, Jiahui Cen wrote:
>> For x86, Linux does not handle the pci resource assignment. But for arm, it
>> would assign all the pci resources, unless we explicitly let Linux preserve
>> PCI resource alignment made by firmware, using "PCI Boot Configuration"
>> _DSM function.
> This difference between x86 and arm seems inexplicable to me.
> 
>> What do you think of adding "PCI Boot Configuration" _DSM function into
>> dsdt table to make kernel use firmware's resource configuration?
> The relevant kernel commits seem to be:
> 
> - 18e94a338436 ("PCI: Make a shareable UUID for PCI firmware ACPI _DSM",
> 2015-04-08)
> 
> - a78cf9657ba5 ("PCI/ACPI: Evaluate PCI Boot Configuration _DSM",
> 2019-06-21)
> 
> I've also read now section "4.6.5. _DSM for Ignoring PCI Boot
> Configurations" in the "PCI(TM) Firmware Specification,
> Revision 3.1, December 13, 2010".
> 
> Basically if this _DSM#5 function exists, it tells the OS whether it is
> required to honor the firmware-assigned resources (value 0), or if it is
> free to reassign (value 1). If the function does not exist at all, then,
> "the operating system may continue to use the legacy handling regarding
> the boot configuration".
> 
> Without knowing more, I consider it a bug that aarch64 Linux uses a
> default strategy (in the absence of the _DSM#5 function) that is the
> opposite of the x86 default. But, you seem to be right that there is a
> specified way to convince arm64 Linux otherwise. Can you indeed add this
> _DSM#5 function to the "virt" machine's ACPI generator, returning value
> 0, and see if it makes a difference?

OK, I've tested adding _DSM#5 function in QEMU, and it seems to work well for
ARM "virt" machine.

Thanks,
Jiahui

  parent reply	other threads:[~2020-12-17 13:52 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-09 13:05 [PATCH v2 0/4] Add extra pci roots support for Arm Jiahui Cen
2020-11-09 13:05 ` [PATCH v2 1/4] OvmfPkg: Extract functions form PciHostBridgeLib Jiahui Cen
2020-11-11 16:45   ` Laszlo Ersek
2020-11-12  3:21     ` Jiahui Cen
2020-11-09 13:05 ` [PATCH v2 2/4] ArmVirtPkg: Use extracted PciHostBridgeUtilityLib Jiahui Cen
2020-11-11 17:27   ` Laszlo Ersek
2020-11-12  3:30     ` [edk2-devel] " Jiahui Cen
2020-11-09 13:05 ` [PATCH v2 3/4] OvmfPkg: Extract functions of extra pci roots Jiahui Cen
2020-11-09 13:05 ` [PATCH v2 4/4] ArmVirtPkg: Support " Jiahui Cen
2020-11-11 14:33 ` [PATCH v2 0/4] Add extra pci roots support for Arm Laszlo Ersek
2020-11-12  3:20   ` [edk2-devel] " Jiahui Cen
2020-12-04  6:48   ` Jiahui Cen
2020-12-04 15:08     ` Laszlo Ersek
2020-12-11 10:57     ` Ni, Ray
2020-12-15 12:52       ` Jiahui Cen
2020-12-17 13:23         ` Laszlo Ersek
2020-12-17 13:37           ` Ard Biesheuvel
2020-12-17 14:42             ` Jonathan Cameron
2020-12-17 13:52           ` Jiahui Cen [this message]
2020-11-12  8:49 ` Ard Biesheuvel
2020-11-13 19:44   ` Laszlo Ersek
2020-11-16  1:33     ` [edk2-devel] " Jiahui Cen

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