linux-kernel - Re: [PATCH v3 03/15] cxl/pci: Introduce PCIe helper functions pcie_is_cxl() and pcie_is_cxl

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Message-ID: <081886d4-90a6-411d-a234-cba5d5e997ba@amd.com>
Date: Tue, 19 Nov 2024 06:20:12 -0600
From: "Bowman, Terry" <terry.bowman@....com>
To: Lukas Wunner <lukas@...ner.de>
Cc: linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-pci@...r.kernel.org, nifan.cxl@...il.com, ming4.li@...el.com,
 dave@...olabs.net, jonathan.cameron@...wei.com, dave.jiang@...el.com,
 alison.schofield@...el.com, vishal.l.verma@...el.com,
 dan.j.williams@...el.com, bhelgaas@...gle.com, mahesh@...ux.ibm.com,
 ira.weiny@...el.com, oohall@...il.com, Benjamin.Cheatham@....com,
 rrichter@....com, nathan.fontenot@....com,
 Smita.KoralahalliChannabasappa@....com
Subject: Re: [PATCH v3 03/15] cxl/pci: Introduce PCIe helper functions
 pcie_is_cxl() and pcie_is_cxl_port()



On 11/17/2024 11:02 AM, Lukas Wunner wrote:
> On Fri, Nov 15, 2024 at 07:54:37AM -0600, Bowman, Terry wrote:
>> On 11/15/2024 2:47 AM, Lukas Wunner wrote:
>>> On Thu, Nov 14, 2024 at 11:07:26AM -0600, Bowman, Terry wrote:
>>>> I will remove the "if (!pcie_is_cxl(dev))" block as you suggested.
>>> Ah, this is meant as a speed-up.  Actually that makes sense,
>>> so feel free to keep it.
>>>
>>> If you do remove it, I think you'll have to move the cxl_port_dvsec()
>>> invocation up in the function, in front of the pci_pcie_type() checks.
>>> The latter require that one first checks that the device is PCIe.
>>> That's done implicitly by cxl_port_dvsec() because it returns 0 in
>>> the non-PCIe case.  (Due to the "if (dev->cfg_size <= PCI_CFG_SPACE_SIZE)"
>>> check in pci_find_next_ext_capability().)
>>>
>>> Another idea would be to put a "if (!pcie_is_cxl(dev)) return 0;" speed-up
>>> in cxl_port_dvsec() so that the other caller benefits from it as well.
>> Ok, I'll look at adding the same pcie_is_cxl() call and check in
>> cxl_port_devsec().
> If you put "if (!pcie_is_cxl(dev)) return 0;" in cxl_port_devsec()
> and move the call to cxl_port_devsec() in pcie_is_cxl_port() up in front
> of the pci_pcie_type() checks, I think you won't need an additional
> "!pcie_is_cxl(dev)" check in pcie_is_cxl_port().
>
> Thanks,
>
> Lukas
Ok. I'll make that change.

Regards,
Terry