Re: [PATCH v2 1/2] Documentation: tpm: add the IBM Virtual TPM device tree binding documentation

[Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Thu, Oct 06, 2016 at 01:44:32AM +0530, Nayna wrote:
> 
> 
> On 09/29/2016 04:34 PM, Jarkko Sakkinen wrote:
> >On Wed, Sep 28, 2016 at 04:30:40AM -0400, Nayna Jain wrote:
> >>Virtual TPM, which is being used on IBM POWER7+ and POWER8 systems running
> >>POWERVM, is currently supported by tpm device driver but lacks the
> >>documentation. This patch adds the missing documentation for the existing
> >>support.
> >>
> >>Suggested-by: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
> >>Signed-off-by: Nayna Jain <nayna-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
> >>---
> >>Changelog v2:
> >>
> >>- New Patch
> >>
> >>  .../devicetree/bindings/security/tpm/ibmvtpm.txt   | 41 ++++++++++++++++++++++
> >>  1 file changed, 41 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/security/tpm/ibmvtpm.txt
> >>
> >>diff --git a/Documentation/devicetree/bindings/security/tpm/ibmvtpm.txt b/Documentation/devicetree/bindings/security/tpm/ibmvtpm.txt
> >>new file mode 100644
> >>index 0000000..d89f999
> >>--- /dev/null
> >>+++ b/Documentation/devicetree/bindings/security/tpm/ibmvtpm.txt
> >>@@ -0,0 +1,41 @@
> >>+* Device Tree Bindings for IBM Virtual Trusted Platform Module(vtpm)
> >>+
> >>+Required properties:
> >>+
> >>+- compatible            : property name that conveys the platform architecture
> >>+                          identifiers, as 'IBM,vtpm'
> >>+- device_type           : specifies type of virtual device
> >
> >A generic device tree question. What is the difference between
> >these fields? Why the I2C one does have 'device_type'?
> 
> Please find the details as below:
> 
> compatible - Standard property name as per IEEE 1275, specifying the
> interface compatible with this device. This property is consumed by linux
> kernel for selection of device driver.
> 
> device_type - Standard property name as per IEEE 1275, specifying the device
> type. This property MAY be used by linux kernel for device driver selection.
> It is used in the case of IBM virtual TPM driver.

AIUI, this should be a standard value such as serial, pci, etc. I don't 
think your use here is correct, but I could be wrong. I'm not certain 
what you do with devices that don't have a standard type.

> 
> /**
>  * vio_register_device_node: - Register a new vio device.
>  * @of_node:    The OF node for this device.
>  *
>  * Creates and initializes a vio_dev structure from the data in
>  * of_node and adds it to the list of virtual devices.
>  * Returns a pointer to the created vio_dev or NULL if node has
>  * NULL device_type or compatible fields.
>  */
> struct vio_dev *vio_register_device_node(struct device_node *of_node)
> 
> and vtpm device table being defined as below:
> 
> static struct vio_device_id tpm_ibmvtpm_device_table[] = {
>         { "IBM,vtpm", "IBM,vtpm"}, ----------------------------------->
> type,compat
>         { "", "" }
> };
> 
> So, vio (virtual) devices uses both device_type and compatible property for
> device registration and driver selection.
> In case of physical TPM, it is only compatible property being used for
> device driver selection
> 
> Also, please note that device_type property is now deprecated in latest
> Device Tree specs.

Deprecated for Flattened DT only. OpenFirmware implementations 
can/should still use this.

Rob

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