linux-kernel - [PATCH libata: add SSD detection hueristic; move SSD setup to ata_dev_configure (was Re: [GIT PULL] Ext3 latency fixes)

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Message-ID: <49DBAC42.4040003@garzik.org>
Date:	Tue, 07 Apr 2009 15:40:50 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Arjan van de Ven <arjan@...radead.org>, Mark Lord <lkml@....ca>,
	Theodore Tso <tytso@....edu>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Linux IDE mailing list <linux-ide@...r.kernel.org>
Subject: [PATCH libata: add SSD detection hueristic; move SSD setup to ata_dev_configure
 (was Re: [GIT PULL] Ext3 latency fixes)

Linus Torvalds wrote:
> 
> On Mon, 6 Apr 2009, Jeff Garzik wrote:
> 
>> Arjan van de Ven wrote:
>>> On Sun, 05 Apr 2009 16:57:21 -0400
>>> Jeff Garzik <jeff@...zik.org> wrote:
>>>> We set it in libata-scsi.c:ata_scsi_dev_config() based on
>>>> ata_id_is_ssd()
>>>>
>>>> That hueristic probably assumes Intel SSDs or something :/
>>> you mean the "rpm" set to '1' ?
>>> I was pretty sure that that was industry standard...
>> A -new- industry standard.  You can certainly create a compliant SSD while
>> only conforming to ATA-7, for example.  Some older IDE flash devices pretend
>> they are normal hard drives in almost every respect, too.
> 
> Something like this might be a good idea. 
> 
> I've seen several SSD's that do _not_ do that whole RPM == 1 thing, but 
> they have "SSD" in their names. 
> 
> I forget how the ID is stored (I have this memory of it being big-endian 
> 16-bit words or something crazy like that?), but aside from fixing up that 
> kind of crazyness, maybe something like this is worth it?
> 
> And making it non-inline, of course. And maybe it should use 'strstr()' 
> instead of checking whether the name ends in 'SSD'. You get the idea..

ata_id_string() or ata_id_c_string() is what you want.

But yeah, we see what you're trying to illustrate.

For internal reasons, it is better to detect and set up SSD details in 
ata_dev_configure(), where we detect and configure other ATA details.

I've attached an example patch, compiled-tested only.

If we wanted to get more fancy, we could extend the strn_pattern_cmp() 
function in libata to accept wildcard '*' prefixes, as well as suffixes. 
  That would make it easy to auto-configure future ATA devices based on 
the product id (such as "G.SKILL 128GB SSD").

	Jeff



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