linux-kernel - Re: [patch 1/7] libata: check for AN support

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Date:	Tue, 24 Apr 2007 20:05:52 +0200
From:	Olivier Galibert <galibert@...ox.com>
To:	Kristen Carlson Accardi <kristen.c.accardi@...el.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, jeff@...zik.org,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-ide@...r.kernel.org, htejun@...il.com
Subject: Re: [patch 1/7] libata: check for AN support

On Tue, Apr 24, 2007 at 08:49:04AM -0700, Kristen Carlson Accardi wrote:
> On Tue, 24 Apr 2007 12:23:04 +0200
> Olivier Galibert <galibert@...ox.com> wrote:
> 
> > Sorry for replying to Alan's reply, I missed the original mail.
> > 
> > > > +#define ata_id_has_AN(id)	\
> > > > +	((id[76] && (~id[76])) & ((id)[78] & (1 << 5)))
> > 
> > (a && ~a) & (b & 32)
> > 
> > I don't think that does what you think it does, because at that point
> > it's a funny way to write 0 ((0 or 1) binary-and (0 or 32)).
> > 
> > I'm not even sure what it is you want.  If for the first part you
> > wanted (id[76] != 0x00 && id[76] != 0xff), please write just that,
> > thanks :-)
> > 
> >   OG.
> > 
> 
> >From the serial ata spec, we have:
> 
> 13.2.1.18        Word 78: Serial ATA features supported
> If Word 76 is not 0000h or FFFFh, Word 78 reports the optional features 
> supported by the device.  Support for this word is optional and if not 
> supported the word shall be zero indicating the device has no support for new 
> Serial ATA capabilities.
> 
> so, basically yes, I'm really testing to make sure that word 76 isn't 0 or all
> one then using that value & with value of bit in work 78 to determine AN
> support - if you think this is really obfuscated, I've got no problem changing 
> it - there's obviously many ways to mess around with bits.

& is not &&, so right now it's really incorrect.  1 & 32 is 0.

((id)[76] != 0x0000 && (id)[76] != 0xffff && ((id)[78] & (1 << 5)))

The implicit typing of id looks dangerous to me, but you're not the
one who has started it.

  OG.
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