Subject: Re: Work-around for certain buggy S-ATA PHYs
To: None <firstname.lastname@example.org>
From: Christos Zoulas <email@example.com>
Date: 03/21/2003 17:15:09
In article <555D6BF8-5BBF-11D7-A7AD-000A957650EC@wasabisystems.com>,
Jason Thorpe <firstname.lastname@example.org> wrote:
i would move the nbp out of the loop and do:
struct *nbp = NULL;
and then at the end do:
if (__predict_false(nbp != NULL))
if (__predict_false((bp->b_flags & B_CALL) != 0 &&
bp->b_iodone == wd_split_mod15_write))
because I am not sure if the above test is adequate, since it does not
match the exact condition of the first if statement (and anyway it is cheaper).
>The following patch fixes some broken behavior I observed with a
>Seagate Serial ATA disk.
>Apparently, the PHY used on some models of Seagate S-ATA drives makes
>an assumption about the way the data is packetized on the wire, and
>some controllers break that assumption when the amount of payload
>*just* fills a S-ATA frame (the controllers are not violating the spec).
>The problem only occurs for writes to the disk.
>The simplest fix is to just split the transfer in two when that
>condition arises. You can detect the condition like so:
> sector_count > 1 && sector_count % 15 == 1
>Obviously, the most common case is that of a 16 sector (8K byte), but I
>have seen 76 sector transfers as well.
>This patch basically does 3 things:
> * Adds quirk support to the wd(4) driver.
> * Detects the condition.
> * Splits the transfer when the condition is detected.
> -- Jason R. Thorpe <email@example.com>
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