linux-kernel - Re: [PATCH 1/4] Introduce ata_id_has

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Date:	Sat, 30 Aug 2008 22:01:35 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Elias Oltmanns <eo@...ensachen.de>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Jeff Garzik <jeff@...zik.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Tejun Heo <htejun@...il.com>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] Introduce ata_id_has_unload()

Elias Oltmanns wrote:

>>>diff --git a/include/linux/ata.h b/include/linux/ata.h
>>>index 80364b6..d9a94bd 100644
>>>--- a/include/linux/ata.h
>>>+++ b/include/linux/ata.h
>>>@@ -707,6 +707,23 @@ static inline int ata_id_has_dword_io(const u16 *id)
>>> 	return 0;
>>> }
>>> +static inline int ata_id_has_unload(const u16 *id)
>>>+{
>>>+	/*
>>>+	 * ATA-7 specifies two places to indicate unload feature
>>>+	 * support. Since I don't really understand the difference,
>>>+	 * I'll just check both and only return zero if none of them
>>>+	 * indicates otherwise.

>>  If you read the comments to the words 82:84 and 85:87, they say that
>>the former indicate the supported features, and the latter indicate
>>the enabed features AND in case a feature can't be disabled, the
>>latter words will have the corresponding bit set. So it should be
>>sufficient to check only one word.

> Yes, I tend to agree with you and, in fact, I have been leaning in this
> direction myself. However, there is something that really bothers me.
> Both entries describing bit 13 of word 87 and 84 are worded alike. In
> particular, it says *supported* in both places, whereas in the case of the
> other features it would say enabled in one and supported in the other
> place.

    I think it says "supported" where the feature can't be disabled and 
"enabled" where it can. Otherwise, this would make a little sense indeed.
Hm, I even found a quote in ATA/PI-7 rev. 4b backing this claim (should've 
pasted it into previous mail):

6.17.43 Words (87:85): Features/command sets enabled

Words (87:85) shall indicate features/command sets enabled. If a defined bit 
is cleared to zero, the indicated features/command set is not enabled. If a 
supported features/command set is supported and cannot be disabled, it is 
defined as supported and the bit shall be set to one.

>>>+	 */
>>>+	if (ata_id_major_version(id) >= 7
>>>+	    && (((id[ATA_ID_CFSSE] & 0xC000) == 0x4000
>>>+		 && id[ATA_ID_CFSSE] & (1 << 13))
>>>+		|| ((id[ATA_ID_CSF_DEFAULT] & 0xC000) == 0x4000
>>>+		    && (id[ATA_ID_CSF_DEFAULT] & (1 << 13)))))
>>>  

>>  I think that it's preferrable to leave the operator on the same line
>>with the first operand...

> Not having too strong an opinion about it, I just thought that an
> operator at the beginning of the line was another indication (apart from
> indentation) that this still belongs to the condition. Still, I can

   Do we need *another* indication? :-)

> change it for the next series round.

> Regards,

> Elias

MBR, Sergei
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