[PATCH] ESP driver

[PATCH] ESP driver

[BERTRAND Joël]

	Hello,

	I think I have found a bug in esp_scsi.c. Without this patch, my 
SS20/SMP was not able to rebuild its internal raid1 volume due to esp0 
DMA errors. With the following patch, same workstation is building a 
kernel, doing a rsync (between two local directories) and rebuilding a 
26 GB raid1 volume without any trouble.

Signed-off-by: BERTRAND Joel <joel.bertrand@systella.fr>

Index: linux/drivers/scsi/esp_scsi.c
=================================--- linux/drivers/scsi/esp_scsi.c.orig 2008-02-18 16:50:14.000000000 +0100
+++ linux/drivers/scsi/esp_scsi.c      2008-02-18 16:52:17.000000000 +0100
@@ -961,6 +961,7 @@
         switch (esp->rev) {
         case ESP100:
         case ESP100A:
+       case FAS100A:
               /* The interrupt pending bit of the status register cannot
                * be trusted on these revisions.
                */


	Regards,

	JKB

Re: [PATCH] ESP driver

[David Miller]

From: BERTRAND_Joël <joel.bertrand@systella.fr>
Date: Mon, 18 Feb 2008 22:34:25 +0100

> 	I think I have found a bug in esp_scsi.c. Without this patch, my 
> SS20/SMP was not able to rebuild its internal raid1 volume due to esp0 
> DMA errors. With the following patch, same workstation is building a 
> kernel, doing a rsync (between two local directories) and rebuilding a 
> 26 GB raid1 volume without any trouble.
> 
> Signed-off-by: BERTRAND Joel <joel.bertrand@systella.fr>

It may correct your problem for some reason, but this change
is not correct (and your email client or your editor used
spaces instead of tab characters in your change).  The FAS100A
implements the ESP_STAT_INTR bit correctly.

If the FAS100A needed this change, you would get spurious IRQs or
other state machine errors, not DMA errors.

I think your change merely changes timings, making the DMA problem
harder to trigger.

I'm sorry I don't have more desirable feedback for your patch, but
it's the best I can do :-)

Re: [PATCH] ESP driver

[BERTRAND Joël]

David Miller wrote:
> From: BERTRAND_Joël <joel.bertrand@systella.fr>
> Date: Mon, 18 Feb 2008 22:34:25 +0100
> 
>> 	I think I have found a bug in esp_scsi.c. Without this patch, my 
>> SS20/SMP was not able to rebuild its internal raid1 volume due to esp0 
>> DMA errors. With the following patch, same workstation is building a 
>> kernel, doing a rsync (between two local directories) and rebuilding a 
>> 26 GB raid1 volume without any trouble.
>>
>> Signed-off-by: BERTRAND Joel <joel.bertrand@systella.fr>
> 
> It may correct your problem for some reason, but this change
> is not correct (and your email client or your editor used
> spaces instead of tab characters in your change).  The FAS100A
> implements the ESP_STAT_INTR bit correctly.
> 
> If the FAS100A needed this change, you would get spurious IRQs or
> other state machine errors, not DMA errors.
> 
> I think your change merely changes timings, making the DMA problem
> harder to trigger.
> 
> I'm sorry I don't have more desirable feedback for your patch, but
> it's the best I can do :-)

	David,

	Only one question. For you, where can I find this bug ? In arch/sparc, 
in shared code or in ESP driver itself ?

	I have seen that DMA errors were allways followed by some ESP resets (I 
think because I can see an AUTOSENSE command on console) but this ESP 
reset command aborts or does not avoid ESP_STAT_INTR flag in esp->sreg. 
Why not reset command does not clear this flag ? I'm not sure that it's 
a mistake, but I don't understand why this flag remains set.

	You said that my patch makes problem harder to trigger. Maybe, but I'm 
pretty sure than this bug is close from this ESP_STAT_INTR flag that is 
not cleared for some reasons on SS20. I have tested my quick and dirty 
patch all night with 6 disks (two internal, four external and a CDROM 
reader). Configuration :

/dev/sda1 + /dev/sdb1 => /boot
/dev/sda2 + /dev/sdb2 => swap
/dev/sda4 + /dev/sdb4 => /
/dev/sda8 + /dev/sdb8 => /opt
/dev/sdc1 + /dev/sdd1 + /dev/sde1 + /dev/sdf1 => /export/home (raid5)

and I have stressed ESP chip without any trouble.

	Regards,

	JKB

Re: [PATCH] ESP driver

[David Miller]

From: BERTRAND_Joël <joel.bertrand@systella.fr>
Date: Tue, 19 Feb 2008 10:20:10 +0100

> 	Only one question. For you, where can I find this bug ? In
> arch/sparc, in shared code or in ESP driver itself ?

I have to be terse and frank with you, I do not have the
time necessary to sit down and teach someone how to debug
these problems.

Besides, you will learn much more about the system if you try to
explore it yourself.