linux-kernel - Re: [PATCH 4/5] platform/x86/intel/ifs: Implement Array BIST test

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Date:   Wed, 1 Feb 2023 11:45:44 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jithu Joseph <jithu.joseph@...el.com>, hdegoede@...hat.com,
        markgross@...nel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        gregkh@...uxfoundation.org, rostedt@...dmis.org,
        ashok.raj@...el.com, tony.luck@...el.com,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        patches@...ts.linux.dev, ravi.v.shankar@...el.com,
        thiago.macieira@...el.com, athenas.jimenez.gonzalez@...el.com,
        sohil.mehta@...el.com
Subject: Re: [PATCH 4/5] platform/x86/intel/ifs: Implement Array BIST test

On 1/31/23 15:43, Jithu Joseph wrote:
> +static void ifs_array_test_core(int cpu, struct device *dev)
> +{
> +	union ifs_array activate, status;
> +	bool timed_out = false;
> +	struct ifs_data *ifsd;
> +	unsigned long timeout;
> +	u64 msrvals[2];
> +
> +	ifsd = ifs_get_data(dev);
> +
> +	activate.data = 0;
> +	activate.array_bitmask = ~0U;
> +	activate.ctrl_result = 0;

I think this whole 'ifs_array' as a union thing is bogus.  It's actually
obfuscating and *COMPLICATING* the code more than anything.  Look what
you have:

	union ifs_array activate; // declare it on the stack, unzeroed

	activate.data = 0; // zero the structure;
	activate.array_bitmask = ~0U; // set one field
	activate.ctrl_result = 0; // set the field to zero again???

Can we make it less obfuscated?  How about:

	struct ifs_array activate = {}; // zero it
	...
	activate.array_bitmask = ~0U; // set the only nonzero field

Voila!  Less code, less obfuscation, less duplicated effort.  Or, worst
case:

	struct ifs_array activate;
	...
	memset(&activate, 0, sizeof(activate));
	activate.array_bitmask = ~0U;

That's sane and everyone knows what it does and doesn't have to know
what unions are involved or how they are used.  It's correct code no
matter *WHAT* craziness lies within 'activate'.