linux-kernel - Re: [PATCH V5 1/3] platform/x86: Add Intel Software Defined Silicon driver

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Date:   Fri, 4 Feb 2022 07:57:02 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "David E. Box" <david.e.box@...ux.intel.com>
Cc:     hdegoede@...hat.com, andriy.shevchenko@...ux.intel.com,
        srinivas.pandruvada@...el.com, mgross@...ux.intel.com,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        Mark Gross <markgross@...nel.org>
Subject: Re: [PATCH V5 1/3] platform/x86: Add Intel Software Defined Silicon
 driver

On Thu, Feb 03, 2022 at 09:30:44PM -0800, David E. Box wrote:
> Intel Software Defined Silicon (SDSi) is a post manufacturing mechanism for
> activating additional silicon features. Features are enabled through a
> license activation process.  The SDSi driver provides a per socket, sysfs
> attribute interface for applications to perform 3 main provisioning
> functions:
> 
> 1. Provision an Authentication Key Certificate (AKC), a key written to
>    internal NVRAM that is used to authenticate a capability specific
>    activation payload.
> 
> 2. Provision a Capability Activation Payload (CAP), a token authenticated
>    using the AKC and applied to the CPU configuration to activate a new
>    feature.
> 
> 3. Read the SDSi State Certificate, containing the CPU configuration
>    state.
> 
> The operations perform function specific mailbox commands that forward the
> requests to SDSi hardware to perform authentication of the payloads and
> enable the silicon configuration (to be made available after power
> cycling).
> 
> The SDSi device itself is enumerated as an auxiliary device from the
> intel_vsec driver and as such has a build dependency on CONFIG_INTEL_VSEC.
> 
> Link: https://github.com/intel/intel-sdsi
> Signed-off-by: David E. Box <david.e.box@...ux.intel.com>
> Reviewed-by: Mark Gross <markgross@...nel.org>
> ---
> V5
>   - Update kernel version to 5.18 in API doc and copyrights to 2022.
>   - Remove unneeded prototypes.
>   - In binary attribute handlers where ret is only used for errors,
>     replace,
>               return (ret < 0) ? ret : size;
>     with,
>               return ret ?: size;

That's horrible, please no.

Will you remember what this does in 5 years when you have to look at it
again?  Spell it out, this saves nothing in runtime or code size:
	if (ret < 0)
		return ret;
	return size;

There, obvious, simple, and can be read by anyone.

thanks,

greg k-h