linux-hardening - Re: [PATCH v1 2/8] dt-bindings: tpm: Add schema for TIS I2C devices

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Date: Thu, 14 Dec 2023 09:37:20 -0600
From: Ninad Palsule <ninad@...ux.ibm.com>
To: Guenter Roeck <linux@...ck-us.net>, Conor Dooley <conor@...nel.org>
Cc: robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        joel@....id.au, andrew@...econstruct.com.au, peterhuewe@....de,
        jarkko@...nel.org, jgg@...pe.ca, keescook@...omium.org,
        tony.luck@...el.com, gpiccoli@...lia.com,
        johannes.holland@...ineon.com, broonie@...nel.org,
        patrick.rudolph@...ements.com, vincent@...emblay.dev,
        peteryin.openbmc@...il.com, lakshmiy@...ibm.com, bhelgaas@...gle.com,
        naresh.solanki@...ements.com, alexander.stein@...tq-group.com,
        festevam@...x.de, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-aspeed@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-hardening@...r.kernel.org, geissonator@...oo.com
Subject: Re: [PATCH v1 2/8] dt-bindings: tpm: Add schema for TIS I2C devices

Hello Guenter,

On 12/12/23 12:20, Guenter Roeck wrote:
> On Tue, Dec 12, 2023 at 05:14:26PM +0000, Conor Dooley wrote:
>> Hey,
>>
>> On Tue, Dec 12, 2023 at 10:39:58AM -0600, Ninad Palsule wrote:
>>> From: Johannes Holland <johannes.holland@...ineon.com>
>>>
>>> Add a dt schema to support device tree bindings
>> "Add bindings for..."
>>
>>> for the generic I2C
>>> physical layer. Refer to the TCG PC Client Platform TPM Profile (PTP)
>>> Specification for TPM 2.0 v1.04 Revision 14.
>>>
>>> This includes descriptions for the Nuvoton and Infineon devices.
>>>
>>> OpenBMC-Staging-Count: 3
>> I have no idea what this is, but it needs to be removed from the patch.
>>
>>> Signed-off-by: Johannes Holland <johannes.holland@...ineon.com>
>>> Signed-off-by: Joel Stanley <joel@....id.au>
>>> Signed-off-by: Ninad Palsule <ninad@...ux.ibm.com>
>>> ---
>>>   .../bindings/security/tpm/tpm-tis-i2c.yaml    | 50 +++++++++++++++++++
>>>   1 file changed, 50 insertions(+)
>>>   create mode 100644 Documentation/devicetree/bindings/security/tpm/tpm-tis-i2c.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/security/tpm/tpm-tis-i2c.yaml b/Documentation/devicetree/bindings/security/tpm/tpm-tis-i2c.yaml
>>> new file mode 100644
>>> index 000000000000..de1e34065748
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/security/tpm/tpm-tis-i2c.yaml
>>> @@ -0,0 +1,50 @@
>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/security/tpm/tpm-tis-i2c.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: I2C PTP based TPM Devices
>>> +
>>> +maintainers:
>>> +  - Johannes Holland <johannes.holland@...ineon.com>
>>> +
>>> +description:
>>> +  Device Tree Bindings for I2C based Trusted Platform Module (TPM).
>> s/Device Tree Bindings for //. Doesn't dt_binding_check now complain if
>> you have this in a title or description?
>>
>>> +properties:
>>> +  $nodename:
>>> +    pattern: "^tpm(@[0-9a-f]+)?$"
>>> +
>>> +  compatible:
>>> +    oneOf:
>>> +      - description: Infineon's Trusted Platform Module (TPM) (SLB9673).
>>> +        items:
>>> +          - const: infineon,slb9673
>>> +          - const: tcg,tpm-tis-i2c
>>> +      - description: Nuvoton's Trusted Platform Module (TPM) (NPCT75x).
>>> +        items:
>>> +          - const: nuvoton,npct75x
>>> +          - const: tcg,tpm-tis-i2c
>>> +      - const: tcg,tpm-tis-i2c
>> IMO this should be removed and this fallback should only be used in
>> combination with device specific compatibles, like you have here for the
>> infineon and nuvoton devices.
> As mentioned in my response to the other patch, "only" isn't sufficient
> since the tacoma devicetree file only references the generic entry.
> It would also make support for chips from other vendors unnecessarily
> complex.
>
> Question should in my opinion be if the non-fallback entries are really
> needed.

Thanks for the response. I think generic option is in-case we have a 
chip whose specific driver is not available.

Regards,

Ninad

>
> Thanks,
> Guenter