linux-kernel - Re: [PATCH v4 1/1] PCI: of: Relax max-link-speed check to support PCIe Gen5/Gen6

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Message-ID: <6b9c522b-4359-433d-905c-85170ba1c3dc@163.com>
Date: Thu, 18 Dec 2025 20:46:30 +0800
From: Hans Zhang <18255117159@....com>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: bhelgaas@...gle.com, helgaas@...nel.org, ilpo.jarvinen@...ux.intel.com,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/1] PCI: of: Relax max-link-speed check to support
 PCIe Gen5/Gen6



On 2025/12/18 20:44, Manivannan Sadhasivam wrote:
> On Thu, Dec 18, 2025 at 07:56:14PM +0800, Hans Zhang wrote:
>>
>>
>> On 2025/12/18 14:31, Manivannan Sadhasivam wrote:
>>> On Wed, Nov 05, 2025 at 09:47:01PM +0800, Hans Zhang wrote:
>>>> The existing code restricted max-link-speed to values 1~4 (Gen1~Gen4),
>>>> but current SOCs using Synopsys/Cadence IP may require Gen5/Gen6 support.
>>>> While DT binding validation already checks this property, the code-level
>>>> validation in of_pci_get_max_link_speed still lags behind, needing an
>>>> update to accommodate newer PCIe generations.
>>>>
>>>> Hardcoded literals in such validation logic create maintainability
>>>> challenges, as they are difficult to track and update when adding
>>>> support for future PCIe link speeds.  To address this, a helper function
>>>> pcie_max_supported_link_speed() is added in drivers/pci/pci.h, which
>>>> calculates the maximum supported link speed generation using existing
>>>> PCIe capability macros (PCI_EXP_LNKCAP_SLS_*). This ensures alignment
>>>> with the kernel's generic PCIe link speed definitions and avoids
>>>> standalone hardcoded values.
>>>>
>>>> The previous hardcoded "4" in the validation check is replaced with a
>>>> call to this helper function, eliminating the need to modify this specific
>>>> code path when extending support for future PCIe generations.
>>>
>>> How can you not modify this function when PCIe 7.0 gets added? It still requires
>>> an update.
>>>
>>> I'd prefer to just drop the check altogether as the callers already have checks
>>> on their own.
>>
>> Hi Mani,
>>
>>
>> Thank you very much for your reply. Do you mean the following modification?
>>
>> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
>> index 3579265f1198..9d3980e425b4 100644
>> --- a/drivers/pci/of.c
>> +++ b/drivers/pci/of.c
>> @@ -890,7 +890,7 @@ int of_pci_get_max_link_speed(struct device_node *node)
>>   	u32 max_link_speed;
>>
>>   	if (of_property_read_u32(node, "max-link-speed", &max_link_speed) ||
>> -	    max_link_speed == 0 || max_link_speed > 4)
>> +	    max_link_speed == 0)
>>   		return -EINVAL;
>>
>>   	return max_link_speed;
>>
> 
> Yes! But you could remove the 0 check also.

Hi Mani,

Okay, thank you.

Best regards,
Hans

> 
> - Mani
>