Re: [PATCH v4 02/10] PCI/IDE: Enumerate Selective Stream IDE capabilities

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Jul 17, 2025 at 11:33:50AM -0700, Dan Williams wrote:
> Link encryption is a new PCIe feature enumerated by "PCIe 6.2 section
> 7.9.26 IDE Extended Capability".
> 
> It is both a standalone port + endpoint capability, and a building block
> for the security protocol defined by "PCIe 6.2 section 11 TEE Device
> Interface Security Protocol (TDISP)". That protocol coordinates device
> security setup between a platform TSM (TEE Security Manager) and a
> device DSM (Device Security Manager). While the platform TSM can
> allocate resources like Stream ID and manage keys, it still requires
> system software to manage the IDE capability register block.
> 
> Add register definitions and basic enumeration in preparation for
> Selective IDE Stream establishment. A follow on change selects the new
> CONFIG_PCI_IDE symbol. Note that while the IDE specification defines
> both a point-to-point "Link Stream" and a Root Port to endpoint
> "Selective Stream", only "Selective Stream" is considered for Linux as
> that is the predominant mode expected by Trusted Execution Environment
> Security Managers (TSMs), and it is the security model that limits the
> number of PCI components within the TCB in a PCIe topology with
> switches.
> 
> Cc: Yilun Xu <yilun.xu@intel.com>
> Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
> Co-developed-by: Alexey Kardashevskiy <aik@amd.com>
> Signed-off-by: Alexey Kardashevskiy <aik@amd.com>
> Co-developed-by: Yilun Xu <yilun.xu@intel.com>
> Signed-off-by: Yilun Xu <yilun.xu@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> +++ b/drivers/pci/Kconfig
> @@ -122,6 +122,20 @@ config XEN_PCIDEV_FRONTEND
>  config PCI_ATS
>  	bool
>  
> +config PCI_IDE
> +	bool
> +
> +config PCI_IDE_STREAM_MAX
> +	int "Maximum number of Selective IDE Streams supported per host bridge" if EXPERT
> +	depends on PCI_IDE
> +	range 1 256
> +	default 64
> +	help
> +	  Set a kernel max for the number of IDE streams the PCI core supports
> +	  per device. While the PCI specification max is 256, the hardware
> +	  platform capability for the foreseeable future is 4 to 8 streams. Bump
> +	  this value up if you have an expert testing need.

Maybe worth expanding IDE once as we did for DOE:

> +
>  config PCI_DOE
>  	bool "Enable PCI Data Object Exchange (DOE) support"