On Thu, Oct 06, 2016 at 01:44:32AM +0530, Nayna wrote:

On 09/29/2016 04:34 PM, Jarkko Sakkinen wrote:

quoted

On Wed, Sep 28, 2016 at 04:30:40AM -0400, Nayna Jain wrote:

quoted

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 <redacted>
---
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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