Re: [PATCH 1/2] hpt366: fix PCI clock detection for HPT374

[Sergei Shtylyov <sshtylyov@ru.mvista.com>]

Bartlomiej Zolnierkiewicz wrote:

>>>>>>>>>>+		if (chip_type == HPT374 && (PCI_FUNC(dev->devfn) & 1)) {
>>>>>>>>>>+			struct pci_dev	*dev1 = pci_get_slot(dev->bus,
>>>>>>>>>>+							     dev->devfn - 1);

>>>>>>>>>Can be NULL

>>>>>>>> Not really. This may not be called if it's NULL -- see hpt374_init_setup().
>>>>>>>>Maybe worth a comment though...

>>>>>>>>>>+			unsigned long io_base = pci_resource_start(dev1, 4);

>>>>>>>>>Kaboom

>>>>>>>> That was a dud bomb. ;-)

>>>>>>>What stops a hot unplug of a 374 from causing that to occur. I don't see

>>>>>>  Pinned as in pci_get_device()? If so, see setup-ide.c:ide_scan_pcibus().
>>>>>>The IDE core does that for me.

>>>>>ide_scan_pcibus() is used iff IDE is built-in.

>>>>>Moreover pci_get_device() holds reference _only_ to the current PCI device
>>>>>(the reference count to @from PCI device is _always_ decremented).

>>>>   Indeed... doesn't it look like a buglet in the IDE core?

>>>It is OK, when ide_scan_pcibus() is not used

>>    But whan it is used?

> Then it keeps the reference to PCI device itself by using pci_get_device()...

    Well, that I know. What I was asking is where the reference is kept after 
the driver init time -- we're still working with the PCI device, so unplagging 
it would be wrong thing to do. Actually, we should never call pci_dev_put() 
since IDE drivers are not unloadable, right?

>>>probing is done by PCI layer
>>>and it keeps the reference to the PCI device in pci_device_probe().

>>>>>>>where you have the other pci_dev pinned on a hotplug on a box set to scan
>>>>>>>the devices in reverse order

>>>>>>  Function 1 will always be skipped, regardless of the scan order.

>>>>>Yes, but init_chipset_hpt366() will still try to access Function 1

>>>>   No!  Re-read the code please: init_chipset_hpt366() won't be called for 
>>>>function 1 if that one is not detected, and only in this case it does function 
>>>>0 access to read the saved f_CNT value.

>>>Argh, thinko on my side.

>>    Alas, it's your thinko, *again*. ;-)

>>>Unfortunately patch needs fixing anyway since the new comment is incorrect
>>>because the reference is kept by hpt366 driver itself - pci_get_slot() in
>>>init_setup_hpt374() - not the IDE core...

>>    Actually, init_setup_hpt374() grabs function 1 to register pair of devices 
>>(in hopes that the callers have already "pinned" function 0), and 
>>init_chipset_hpt366() "pins" function 0 to read the saved f_CNT.

> Yep, this would make a nice code comment instead the current one. :)

   Ugh, will try to reword it... :-|

> Bart

MBR, Sergei