linux-kernel - Re: [PATCH] x86: OLPC: add support for calling into OpenFirmware (v4)

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Message-ID: <4C1A6AE9.2020307@zytor.com>
Date:	Thu, 17 Jun 2010 11:35:21 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andres Salomon <dilinger@...ued.net>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	x86@...nel.org, Mitch Bradley <wmb@...top.org>
Subject: Re: [PATCH] x86: OLPC: add support for calling into OpenFirmware
 (v4)

On 06/16/2010 07:32 PM, Andres Salomon wrote:
> 
> Add support for saving OFW's cif, and later calling into it to run OFW
> commands.  OFW remains resident in memory, living within virtual range
> 0xff800000 - 0xffc00000.  A single page directory entry points to the
> pgdir that OFW actually uses, so rather than saving the entire page
> table, we grab and install that one entry permanently in the kernel's
> page table.
> 
> This is currently only used by the OLPC XO.
> 

OK, down to the nitpick level...

> +
> +/* page dir entry containing OFW's pgdir table; filled in by head_32.S */
> +pgd_t *olpc_ofw_pgd __initdata;
> +

This is a physical address, not a pointer.  As such it should be
physaddr_t or u32.

> +static DEFINE_SPINLOCK(ofw_lock);
> +
> +#define MAXARGS 10
> +
> +void __init setup_olpc_ofw_pgd(void)
> +{
> +	pgd_t *base, *pde, *ofw_pde;
> +
> +	if (!olpc_ofw_cif)
> +		return;
> +
> +	/* fetch the kernel's current PDE */
> +	base = __va(read_cr3());
> +	pde = &base[OLPC_OFW_PDE_NR];
> +

Since you're touching this so early, you already know that you're
manipulating swapper_pg_dir.  If you *didn't* know that, the above code
would be wrong, since the change you're about to make wouldn't propagate
to other kernel tasks.

So just use swapper_pg_dir[OLPC_OFW_PDE_NR] directly.

	-hpa
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