On Tue, Jun 07, 2016 at 09:03:18AM +0200, Andrew Jones wrote:
> On Tue, Jun 07, 2016 at 08:38:55AM +0200, Alexander Gordeev wrote:
> > On Mon, Jun 06, 2016 at 04:12:03PM +0200, Andrew Jones wrote:
> > > > +phys_addr_t pci_bar_size(pcidevaddr_t dev, int bar_num)
> > > > {
> > > > uint32_t bar = pci_config_readl(dev, PCI_BASE_ADDRESS_0 + bar_num * 4);
> > > > + phys_addr_t size = (int32_t)pci_bar_size32(dev, bar_num);
> > > > + phys_addr_t mask = (int32_t)pci_bar_mask(bar);
> > > >
> > > > - if (bar & PCI_BASE_ADDRESS_SPACE_IO)
> > > > - return bar & PCI_BASE_ADDRESS_IO_MASK;
> > > > - else
> > > > - return bar & PCI_BASE_ADDRESS_MEM_MASK;
> > > > + if (pci_bar_is64(dev, bar_num)) {
> > > > + uint32_t size_high = pci_bar_size32(dev, bar_num + 1);
> > > > + size = ((phys_addr_t)size_high << 32) | (uint32_t)size;
> > > > + }
> > > > +
> > > > + return (~(size & mask)) + 1;
> > >
> > > All this casting of size and mask is pointless. Please rework it
> > > similar to what I did above.
> >
> > This is the most compact and straight variant I was able to come up with:
> >
> > uint32_t bar = pci_bar_get(dev, bar_num);
> > phys_addr_t size = (int32_t)pci_bar_size32(dev, bar_num);
>
> But this is wrong. If your 32-bit size was 0x80000000, then you now
> say it's 0xffffffff80000000.
Hmm.. I am either terribly missing the point or we are on different
pages.
So if pci_bar_size32() returned 0x80000000 the size sign-extension
gives 0xffffffff80000000 and the mask sign extension gives (i.e.
mmio) 0xfffffffffffffff0. The AND gives 0xffffffff80000000 and the
NOT gives 0x7fffffff. Finally, 0x7fffffff + 1 gives 0x80000000.
If we do not sign-extend (or explicitly OR with 0xffffffff00000000)
size and/or mask then the return(~(size & mask)) + 1 gives a wrong
0xffffffff80000000.
> > phys_addr_t mask = (int32_t)pci_bar_mask(bar);
>
> It might be OK to do that here, on a mask, but even if it is, then I
> don't like it, because it's too subtle (like I said for the casting
> in pci_bar_addr in my last reply). I don't like that it requires us to
> know that masking bit 31 in a 32-bit mask means we also want to mask
> 63..32. That should at least be in a comment somewhere.
Yes, but it is not an arbitrary mask, it is an alignment mask.
We unconditionally want to mask 63..32, 31th and even lower.
> > if (pci_bar_is64(dev, bar_num))
> > size |= (phys_addr_t)pci_bar_size32(dev, bar_num + 1) << 32;
> >
> > return (~(size & mask)) + 1;
> >
> > The casting is needed to avoid putting explicitly all 1s into higher
> > bits of size and/or mask. Otherwise (~(size & mask)) + 1 expression would
> > not bring correct results. I really struggle to make something better
> > readable.
>
> It's not just about readability, it's about correctness. You shouldn't
> use 32-bit sizes/masks with 64-bit data this way. Like I said in the
> last reply, you should rework it like I showed you, operate on the
> 32-bit data with the 32-bit mask/size, and then eventually construct
> 64-bit data.
It is all about those last +1 and shifting bits from lower to upper
word of 64-bit value. My hope was to off-load it to the compiler :)
> Thanks,
> drew
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