Re: [PATCH v2 1/2] tpm: devicetree: document properties for cr50

Rob Herring
2016-07-20T19:03:08Z

On Tue, Jul 19, 2016 at 08:41:24PM -0700, Andrey Pronin wrote:
> Add TPM2.0 PTP FIFO compatible SPI interface for chips with Cr50
> firmware. Several timing-related properties that may differ from
> one firmware version to another are added to devicetree.
> Document these properties.
>
> Signed-off-by: Andrey Pronin <apronin@chromium.org>
> ---
> .../devicetree/bindings/security/tpm/cr50_spi.txt | 32 ++++++++++++++++++++++
> 1 file changed, 32 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/security/tpm/cr50_spi.txt
>
> diff --git a/Documentation/devicetree/bindings/security/tpm/cr50_spi.txt b/Documentation/devicetree/bindings/security/tpm/cr50_spi.txt
> new file mode 100644
> index 0000000..f212b6b
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/security/tpm/cr50_spi.txt
> @@ -0,0 +1,32 @@
> +* H1 Secure Microcontroller with Cr50 Firmware on SPI Bus.
> +
> +H1 Secure Microcontroller running Cr50 firmware provides several
> +functions, including TPM-like functionality. It communicates over
> +SPI using the FIFO protocol described in the PTP Spec, section 6.
> +
> +Required properties:
> +- compatible: Should be "google,cr50".
> +- spi-max-frequency: Maximum SPI frequency.
> +
> +Optional properties:
> +- access-delay-ms: Required delay between subsequent transactions on SPI.

As I mentioned, there may be common properties. It doesn't seem you
looked, so I did:

- spi-rx-delay-us - (optional) Microsecond delay after a read transfer.
- spi-tx-delay-us - (optional) Microsecond delay after a write transfer.

Seems to me setting one or both of these should work for you.

> +- sleep-delay-ms: Time after the last SPI activity, after which the chip
> + may go to sleep.
> +- wake-start-delay-ms: Time after initiating wake up before the chip is
> + ready to accept commands over SPI.

I also asked why these 2 can't be hard-coded in the driver?

> +
> +Example:
> +
> +&spi0 {
> + status = "okay";
> +
> + cr50@0 {
> + compatible = "google,cr50";
> + reg = <0>;
> + spi-max-frequency = <800000>;
> +
> + access-delay-ms = <2>;
> + sleep-delay-ms = <1000>;
> + wake-start-delay-ms = <60>;
> + };
> +};
> --
> 2.6.6
>