Re: [RFC PATCH 0/3] lspci: Display cxl1.1 device link status

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Wed, 20 Dec 2023 14:07:35 +0900
KobayashiDaisuke <kobayashi.da-06@fujitsu.com> wrote:

> Hello.
> 
> This patch series adds a feature to lspci that displays the link status
> of the CXL1.1 device.
> 
> CXL devices are extensions of PCIe. Therefore, from CXL2.0 onwards,
> the link status can be output in the same way as traditional PCIe.
> However, unlike devices from CXL2.0 onwards, CXL1.1 requires a
> different method to obtain the link status from traditional PCIe.
> This is because the link status of the CXL1.1 device is not mapped
> in the configuration space (as per cxl3.0 specification 8.1).
> Instead, the configuration space containing the link status is mapped
> to the memory mapped register region (as per cxl3.0 specification 8.2,
> Table 8-18). Therefore, the current lspci has a problem where it does
> not display the link status of the CXL1.1 device. 
> This patch solves these issues.
> 
> The method of acquisition is in the order of obtaining the device UID,
> obtaining the base address from CEDT, and then obtaining the link
> status from memory mapped register. Considered outputting with the cxl
> command due to the scope of the CXL specification, but devices from
> CXL2.0 onwards can be output in the same way as traditional PCIe.
> Therefore, it would be better to make the lspci command compatible with
> the CXL1.1 device for compatibility reasons.
> 
> I look forward to any comments you may have.
Yikes. 

My gut feeling is that you shouldn't need to do this level of hackery.

If we need this information to be exposed to tooling then we should
add support to the kernel to export it somewhere in sysfs and read that
directly.  Do we need it to be available in absence of the CXL driver
stack? 

Jonathan
> 
> KobayashiDaisuke (3):
>   Add function to display cxl1.1 device link status
>   Implement a function to get cxl1.1 device uid
>   Implement a function to get a RCRB Base address
> 
>  ls-caps.c | 216 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  lspci.h   |  35 +++++++++
>  2 files changed, 251 insertions(+)
>