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Date: Wed, 23 May 2012 12:04:03 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] ahci: SATA FIS is 20 bytes, not 0x20
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To: Alexander Graf <agraf@suse.de>
Cc: "Stefan Weil (commit_signer:2/19=11%)" <sw@weilnetz.de>, "Anthony Liguori (commit_signer:6/19=32%)" <aliguori@us.ibm.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, =?ISO-8859-1?Q?=22Andreas_F=E4rber_=28commit=5Fsigner=3A2/19=3D11=25?= =?ISO-8859-1?Q?=29=22?= <afaerber@suse.de>, Daniel Verkamp <daniel@drv.nu>

Am 23.05.2012 11:53, schrieb Alexander Graf:
> 
> 
> Am 23.05.2012 um 11:13 schrieb Kevin Wolf <kwolf@redhat.com>:
> 
>> Am 23.05.2012 01:26, schrieb Daniel Verkamp:
>>> As in the SATA and AHCI specifications, a FIS is 5 Dwords of 4 bytes
>>> each, which comes to 20 bytes (decimal), not 0x20.
> 
> Not sure I understand. FISs can have different sizes depending on the payload they are. The one you are looking at here is the d2h init FIS.
> 
> From the SATA 1.0a spec:
> 
> FIS Type - Set to a value of 34h. Defines the rest of the FIS fields. Defines the length of the
> FIS as five Dwords.
> 
> So yes, you are right. The register FIS is 20 bytes, not 0x20 bytes long.
> 
> Does this fix some actual breakage for you?

In theory the SDBFIS could be overwritten with zeros. No idea what this
means or if it matters in practice.

Kevin