Re: [PATCH RFC 3/3] Expose the CPU/Steering Tag mapping via debugfs

[sashiko-bot@kernel.org]

> Steering Tags (ST) are opaque, platform specific values obtained from the
> ACPI ST _DSM, and are only visible to the driver that asks for them. That
> makes it hard to validate whether firmware reports a sane mapping at all.
> 
> Expose the mapping read-only in the debugfs directory of each Root Port
> that has ST _DSM support:
> 
>   # cat /sys/kernel/debug/pci/0000:00:01.1/tph_cpu_st
>   cpu  vm_st  vm_xst vm_ph_ignore pm_st  pm_xst pm_ph_ignore
>   0    0x03   0x0103 0            -      -      0
>   1    0x03   0x0103 0            -      -      0
> 
> Each line holds the raw ST info the _DSM returns for one online CPU;
> invalid tags and failed queries are reported as "-".
> 
> The interface is per Root Port because the _DSM is evaluated on the ACPI
> device of the host bridge above it. A system with multiple host bridges may
> return different tags for the same CPU, and the value that matters to a
> driver is the one for the Root Port its device sits below. Root Ports below
> the same host bridge report identical contents.
> 
> The file is created during enumeration and removed with the device's
> debugfs directory in pci_destroy_dev(), which returns only once no read is
> running, so the pci_dev the file refers to stays valid.
> 
> Signed-off-by: Wei Huang <wei.huang2@amd.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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