linux-kernel - Re: [PATCH v14 2/5] x86/boot: Introduce efi_get_rsdp

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Message-ID: <20181217173605.GA14613@gmail.com>
Date:   Mon, 17 Dec 2018 18:36:05 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, bp@...en8.de,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        keescook@...omium.org, bhe@...hat.com, msys.mizuma@...il.com,
        indou.takao@...fujitsu.com, caoj.fnst@...fujitsu.com
Subject: Re: [PATCH v14 2/5] x86/boot: Introduce efi_get_rsdp_addr() to find
 RSDP from EFI table

* Ingo Molnar <mingo@...nel.org> wrote:

> > +		if (!(efi_guidcmp(guid, ACPI_TABLE_GUID)))
> > +			rsdp_addr = (acpi_physical_address)table;
> > +		else if (!(efi_guidcmp(guid, ACPI_20_TABLE_GUID)))
> > +			return (acpi_physical_address)table;
> 
> 'return' is not a function.

Disregard this - I got confused by the type cast.

The type cast is ugly nevertheless. 'table' is an 'unsigned long'.

So 'acpi_physical_address' is basically an u64/u32, depending on 
ACPI_MACHINE_WIDTH, right?

Since this is x86, can ACPI_MACHINE_WIDTH ever get out of sync with the 
native 'unsigned long' size?

If not then why not make the return type 'unsigned long', instead of 
'acpi_physical_address' that you have to wade through a couple of headers 
to figure out its true size. Does that cause complications elsewhere?

I.e. the excessive type casts are ugly and make the code somewhat 
fragile.

Thanks,

	Ingo