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Subject: 48-bit Drives Incorrectly reporting 255 Heads?
Date: Wed, 20 Aug 2003 13:31:08 -0600
Message-ID: <88A7BC80FA2797498AF6D865CAD3EA43180E95@iceman.altiris.com>
Thread-Topic: 48-bit Drives Incorrectly reporting 255 Heads?
Thread-Index: AcNnUZHIlzrV20pMQz2H5RAqp7PARg==
From: "John Riggs" <jriggs@altiris.com>
To: <linux-kernel@vger.kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1187
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  With the 2.4.20 kernel, I have a 40GB disk with 240 heads, with 48-bit
mode enabled. The Linux ide driver automatically declares that anything
with 48-bit mode enabled has 255 heads. This is a problem, as I am
writing a utility to fix up a Windows PBR, and the PBR relies on the
head count as counted by the BIOS.
  The Linux code in question is in ide-disk.c:

  if (id->cfs_enable_2 & 0x0400) {
    .
    drive->head = drive->bios_head = 255;
    .
  }

  What I would like to do is change the above to:

  if (id->cfs_enable_2 & 0x0400) {
    .
    drive->head = 255;
    .
  }

  Thereby not changing the bios head count. My initial tests seem to
have worked okay, with the correct geometry getting reported. Can
anybody point out to me why this will break something else?
  Two more specific questions are:
    1) Will this break drives > 137 GB?
    2) Why would the head count be set to 255 in the first place?

Thank you,
John Riggs
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