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?

> 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.

> Thanks,
> Bart

MBR, Sergei