libata/ipr/powerpc: regression between 2.6.39-rc4 and 2.6.39-rc5

Nishanth Aravamudan
2011-06-15T19:18:22Z

Hi Jeff,

It appears that commit 7b3a24c57d2eeda8dba9c205342b12689c4679f9 broke
CD-ROMs on the IPR SATA bus on powerpc machines:

ata_port_alloc: ENTER
ata_port_probe: ata1: bus probe begin
ata1.00: ata_dev_read_id: ENTER
ata1.00: failed to IDENTIFY (I/O error, err_mask=0x40)
ata1.00: ata_dev_read_id: ENTER
ata1.00: failed to IDENTIFY (I/O error, err_mask=0x40)
ata1.00: limiting speed to UDMA7:PIO5
ata1.00: ata_dev_read_id: ENTER
ata1.00: failed to IDENTIFY (I/O error, err_mask=0x40)
ata1.00: disabled
ata_port_probe: ata1: bus probe end
scsi_alloc_sdev: Allocation failure during SCSI scanning, some SCSI devices might not be configured

The commit in question is tagged as AHCI, but does touch the libata
core. I'm not well-versed with this code, but here's what I think I know
:)

>From __scsi_add_device, we first allocate the target:

scsi_alloc_target ->
shost->hostt->target_alloc ->
ipr_target_alloc ->
ata_port_alloc ->
sets FROZEN

We error out when we allocate the sdev:

scsi_alloc_sdev ->
shost->hostt->slave_alloc ->
ipr_slave_alloc ->
ipr_ata_slave_alloc ->
ata_sas_port_init ->
ata_port_probe

>From what I can tell, the only place that explicitly clears the FROZEN
flag is the error-handling code via ata_eh_thaw_port().

So I thought either we're not invoking the error-handler at probe time
correctly to kick the port or perhaps the SAS code is not clearing the
flag?

I tried the following patch:

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index d51f979..abd0e0b 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -3797,6 +3797,7 @@ EXPORT_SYMBOL_GPL(ata_sas_port_alloc);
*/
int ata_sas_port_start(struct ata_port *ap)
{
+ ap->pflags &= ~ATA_PFLAG_FROZEN;
return 0;
}
EXPORT_SYMBOL_GPL(ata_sas_port_start);

and the CD-ROM drive works, but I have no idea if it's the right thing
to do. I chose this particular change, FWIW, because we call
ata_sas_port_start before we probe in ata_sas_port_init and it seems
like we need to mark the port as not frozen before we init it? Perhaps
that should really be a call to a thaw function, not sure. Let's just
say the ATA/SAS/SCSI interactions are a bit hard to follow at first :)

Any insight you can provide would be great!

Thanks,
Nish

--
Nishanth Aravamudan <nacc@us.ibm.com>