linux-kernel - Re: [RFC][Patch] IBM Real-Time "SMI Free" mode drive -v2

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Date:	Wed, 16 Dec 2009 00:02:58 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Keith Mannthey <kmannth@...ibm.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	John Stultz <johnstul@...ibm.com>
Subject: Re: [RFC][Patch] IBM Real-Time "SMI Free" mode drive -v2

> --- linux-2.6.32/drivers/misc/ibmrtl/ibm_rtl.c	1969-12-31 16:00:00.000000000 -0800
> +++ linux-2.6.32-rtl/drivers/misc/ibmrtl/ibm_rtl.c	2009-12-14 16:37:19.000000000 -0800

Probably belongs in drivers/firmware as its not a misc_* interface user.

> +	/* Get the address for the Extende Biso Data Area */
> +	ebda_addr = *(u16 *) phys_to_virt(EDBA_ADDR);
> +	ebda_addr <<= 4;
> +	edba_map = ioremap(ebda_addr, 4);
> +	if (!edba_map)
> +		return -ENOMEM;

This is wrong. I wish we had a single proper EBDA handling function
because this keeps coming up.

The rules for the EBDA on PC class hardware as that the EBDA address
provides a real segment offset for the EBDA *if one is present*. Lots of
machines including quite a few suprisingly modern boxes (eg AMD76x
systems without a PS/2 mouse plugged in) don't have an EBDA so you need
to check if the word you read is zero before doing an ioremap.

> +	for (table = (u32 *) edba_map ; \
> +			table < (u32 *) edba_map + ebda_size/4; table++)

You need to check the table is valid and has a correct signature. Not
doing so is completely unsafe.

The rest of the code looks pretty sane to me.

Alan
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