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

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Date:	Sun, 19 Oct 2008 20:52:47 +0200
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Jens Axboe <jens.axboe@...cle.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 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...

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

Thanks,
Bart
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