linux-kernel - Re: [PATCH] PCI: dwc: Add the sysfs property to provide the LTSSM status of the PCIe link

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Message-ID: <5e0196ec-41f8-4969-bd6d-febd5be5048a@163.com>
Date: Sun, 26 Jan 2025 22:06:52 +0800
From: Hans Zhang <18255117159@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: jingoohan1@...il.com, manivannan.sadhasivam@...aro.org,
 lpieralisi@...nel.org, kw@...ux.com, robh@...nel.org, bhelgaas@...gle.com,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, rockswang7@...il.com
Subject: Re: [PATCH] PCI: dwc: Add the sysfs property to provide the LTSSM
 status of the PCIe link



On 2025/1/24 00:49, Bjorn Helgaas wrote:
> On Thu, Jan 23, 2025 at 03:13:26PM +0800, Hans Zhang wrote:
>> Add the sysfs property to provide a view of the current link's LTSSM
>> status from the root port device.
>>
>>    /sys/bus/pci/devices/<dev>/ltssm_status
> 
> Would need a rationale, i.e., what benefit this provides.  Obviously
> this is currently only implemented for DWC-based controllers and
> probably not ever available for ACPI or other generic host bridges.
> 
> Also documentation somewhere in
> Documentation/ABI/testing/sysfs-bus-pci*.
> 
> LTSSM is applicable to all Downstream Ports, including both Root Ports
> and Switch Downstream Ports, but in general I doubt this information
> is available for Switches in any generic way.
> 
>> +++ b/drivers/pci/pci-sysfs.c
>> @@ -1696,6 +1696,9 @@ const struct attribute_group *pci_dev_attr_groups[] = {
>>   #endif
>>   #ifdef CONFIG_PCIEASPM
>>   	&aspm_ctrl_attr_group,
>> +#endif
>> +#ifdef CONFIG_PCIE_DW_HOST
>> +	&dw_ltssm_status_attr_group,
>>   #endif
> 
> I'm not convinced of the value of potentially dozens of device- or
> vendor-specific additions like this.


At present, someone has submitted the dwc common debugfs driver.

dwc common driver: add debugfs
https://lore.kernel.org/linux-pci/20250121111421.35437-3-shradha.t@samsung.com/


I will make a patch version based on this patch.

Best regards
Hans