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

[Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>]

On Saturday 11 August 2007, Sergei Shtylyov wrote:
> 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()...

> > 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. :)

Bart