Re: totally random "VFS: Cannot open root device"

["Jean-François Stenuit" <jfs@keytradebank.com>]

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Hi Tejun,

Thanks for taking the time to check.

Output of your trace with ata_piix.override_PCS=0
  1st boot : success : combined=0 orig_mask=0x11
  2nd boot : success : combined=0 orig_mask=0x11
  3rd boot : failure : combined=0 orig_mask=0x0
  4th boot : failure : combined=0 orig_mask=0x0
  5th boot : failure : combined=0 orig_mask=0x0
  6th boot : failure : combined=0 orig_mask=0x0
  7th boot : success : combined=0 orig_mask=0x11
Output of your trace with ata_piix.override_PCS=1
  1st boot : success : combined=0 orig_mask=0x0
  2nd boot : success : combined=0 orig_mask=0x0
  3rd boot : success : combined=0 orig_mask=0x0
  4th boot : success : combined=0 orig_mask=0x0
  5th boot : success : combined=0 orig_mask=0x0
  6th boot : success : combined=0 orig_mask=0x0
  7th boot : success : combined=0 orig_mask=0x0
  8th boot : success : combined=0 orig_mask=0x0

Looks like you have found a fix/workaround for this bug (but it still 
does not give the reason why it's failing).

Tejun Heo wrote:

>On Thu, Dec 01, 2005 at 10:40:18AM +0100, Jean-Fran?ois Stenuit wrote:
>  
>
>>Hi Keith,
>>
>>I have been able to reproduce the bug (randomly - needing a few reboots 
>>to make it happen) on a 2.6.15-rc3 kernel.
>>
>>System is an HP DL140G2 with following SATA controller (from lspci -vv) :
>>
>>0000:00:1f.2 IDE interface: Intel Corp. 82801EB (ICH5) Serial ATA 150 
>>Storage Controller (rev 02) (prog-if 8a [Master SecP PriP])
>>       Subsystem: Hewlett-Packard Company: Unknown device 3208
>>       Control: I/O+ Mem- BusMaster+ SpecCycle- MemWINV- VGASnoop- 
>>ParErr- Stepping- SERR- FastB2B-
>>       Status: Cap- 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- 
>><TAbort- <MAbort- >SERR- <PERR-
>>       Latency: 0
>>       Interrupt: pin A routed to IRQ 17
>>       Region 0: I/O ports at <unassigned>
>>       Region 1: I/O ports at <unassigned>
>>       Region 2: I/O ports at <unassigned>
>>       Region 3: I/O ports at <unassigned>
>>       Region 4: I/O ports at 1470 [size=16]
>>    
>>
>
>Hi,
>
>Can you try the following patch?  It adds a module parameter
>override_PCS.  If your piix module is built into the kernel, adding
>the following to the kernel paramter shoudl work.
>
>ata_piix.override_PCS=n
>
>Where, n is one of
>
>0: normal behavior
>1: ignore PCS and always try to probe ports
>2: overwrite PCS such that all ENABLED bits are 1
>
>First, try with override_PCS=0 and make not of the printed combined
>and orig_mask values on success and failure cases.  Then, try with
>override_PCS=1, if it also fails, try with override_PCS=2.
>
>You can tell if an override option works or not by comparing the
>combined and orig_mask value to the failure case.  If the machine
>boots successfully with the same combined/orig_mask values as the
>failure case, it means that the override option works.
>
>BTW, all these are based on the previous message in which you said
>that when boot failed the kernel printed the following log message.
>
>"ata1: SATA port has no device."
>
>Right?
>
>
>diff --git a/drivers/scsi/ata_piix.c b/drivers/scsi/ata_piix.c
>index 887b2b9..639da80 100644
>--- a/drivers/scsi/ata_piix.c
>+++ b/drivers/scsi/ata_piix.c
>@@ -340,6 +340,9 @@ static void piix_pata_phy_reset(struct a
> 	ata_bus_reset(ap);
> }
> 
>+static int override_PCS;
>+module_param(override_PCS, int, 0700);
>+
> /**
>  *	piix_sata_probe - Probe PCI device for present SATA devices
>  *	@ap: Port associated with the PCI device we wish to probe
>@@ -367,6 +370,17 @@ static int piix_sata_probe (struct ata_p
> 
> 	pci_read_config_byte(pdev, ICH5_PCS, &pcs);
> 	orig_mask = (int) pcs & 0xff;
>+	printk("ata%u: combined=%d orig_mask=0x%x\n", ap->id, combined, orig_mask);
>+
>+	switch (override_PCS) {
>+	case 1:
>+		printk("ata%u: ignoring PCS\n", ap->id);
>+		return 1;
>+	case 2:
>+		printk("ata%u: turning on PCS ENABLED bits\n", ap->id);
>+		pci_write_config_byte(pdev, ICH5_PCS, 0x0f);
>+		return 1;
>+	}
> 
> 	/* TODO: this is vaguely wrong for ICH6 combined mode,
> 	 * where only two of the four SATA ports are mapped
>
>  
>


-- 
Jean-François "Jef" Stenuit
Network & Security manager
Keytrade Bank SA


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