linux-kernel - Re: [PATCH] ata: ata_id_is

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Message-ID: <20081019191202.GW19428@kernel.dk>
Date:	Sun, 19 Oct 2008 21:12:02 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	Jeff Garzik <jgarzik@...ox.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] ata: ata_id_is_ssd() bugfix

On Sun, Oct 19 2008, Bartlomiej Zolnierkiewicz wrote:
> On Sunday 19 October 2008, Jens Axboe wrote:
> > On Sat, Oct 18 2008, Bartlomiej Zolnierkiewicz wrote:
> > > We need to explicitly check for major and minor version
> > > of supported ATA spec as earlier revisions used word 217
> > > for different purposes.
> > 
> > What did they use to put in that word? Just curious if it does any harm,
> > 
> > because as it stands, this patch will prevent ANY ssd from being
> > correctly flagged as such. So I'm inclined to file this as too much spec
> > fiddling, it'll do more harm than good.
> 
> IIRC it was marked as Reserved for < ATA8 (however I didn't go through
> all previous specs) and some ATA8 minor versions (i.e. 3f) put "NV Cache
> Read Transfer Speed in MB/s" there.
> 
> Well, we may also drop minor versions checking assuming that no NV Cache
> actually will have 1MB/s speed and major version checking assuming that
> no vendor put anything special there but this would need an ACK from Alan
> and maybe a comment on why we do it...

OK, so it's just NV cache. I'd consider that a non-issue.

> > > [ The issue was originally spotted by Alan Cox. ]
> > > 
> > > This patch fixes regression introduced by:
> > > commit 8bff7c6b0f63c7ee9c5e3a076338d74125b8debb
> > > ("libata: set queue SSD flag for SSD devices").
> > > 
> > > Cc: Jeff Garzik <jgarzik@...ox.com>
> > > Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
> > > Cc: Jens Axboe <jens.axboe@...cle.com>
> > > Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
> > > ---
> > > somebody owe me one for going through all these spec drafts... ;)
> > > 
> > >  include/linux/ata.h |    8 +++++++-
> > >  1 file changed, 7 insertions(+), 1 deletion(-)
> > > 
> > > Index: b/include/linux/ata.h
> > > ===================================================================
> > > --- a/include/linux/ata.h
> > > +++ b/include/linux/ata.h
> > > @@ -75,6 +75,7 @@ enum {
> > >  	ATA_ID_EIDE_PIO_IORDY	= 68,
> > >  	ATA_ID_QUEUE_DEPTH	= 75,
> > >  	ATA_ID_MAJOR_VER	= 80,
> > > +	ATA_ID_MINOR_VER	= 81,
> > >  	ATA_ID_COMMAND_SET_1	= 82,
> > >  	ATA_ID_COMMAND_SET_2	= 83,
> > >  	ATA_ID_CFSSE		= 84,
> > > @@ -743,7 +744,12 @@ static inline int ata_id_is_cfa(const u1
> > >  
> > >  static inline int ata_id_is_ssd(const u16 *id)
> > >  {
> > > -	return id[ATA_ID_ROT_SPEED] == 0x01;
> > > +	/* ATA8-ACS version 4c or higher (=> 4c or 6 at the moment) */
> > > +	if (ata_id_major_version(id) >= 8 &&
> > > +	    (id[ATA_ID_MINOR_VER] == 0x39 || id[ATA_ID_MINOR_VER] == 0x28) &&
> > > +	    id[ATA_ID_ROT_SPEED] == 0x01)
> > > +		return 1;
> > > +	return 0;
> > 
> > Is the check even correct? It'll match version 8 AND the currently
> > listed minor version, not newer.
> 
> Checking minor versions is a non-trivial bussiness and improvements
> are welcomed (though ATA8-ACS version 6 is the newest revision ATM).
> 
> It could also be that the we should be checking something else than
> the ATA_ID_ROT_SPEED to detect SSDs reliably but I don't know and don't
> have time currently to look into it.  In the future please post ATA

Rotation speed == 1 is THE way to check for an SSD. The problem is just
that lots of drives are out there and don't claim ATA8 compliance, since
it was finalized until last month. Most of them SHOULD use word 217
though, the ones I looked at sure do.

> patches to linux-ide@ so issues can be spotted and discussed early...

As I already mentioned, it was not even intended to go upstream. It was
committed for testing and I left it in by mistake.

-- 
Jens Axboe

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