> Hi Yakui,
>
> On Tue, Jun 24, 2008 at 10:39 PM, Zhao Yakui <yakui.zhao@intel.com> wrote:
> > On Tue, 2008-06-24 at 21:17 -0700, Alok kataria wrote:
> >> On Tue, Jun 24, 2008 at 7:49 PM, Zhao Yakui <yakui.zhao@intel.com> wrote:
> >> > On Tue, 2008-06-24 at 11:48 -0700, Alok Kataria wrote:
> >> >> Evaluates the _CRS object under PCI0 looking for producer resources.
> >> >> Then searches the e820 memory space for a gap within these producer resources.
> >> >>
> >> >> Allows us to find a gap for the unclaimed pci resources or MMIO resources
> >> >> for hotplug devices within the BIOS allowed pci regions.
> >> >>
> >> > It seems reasonable.
> >> > But if the resource obtained from the PCI0 _CRS method is incorrect, we
> >> > will get the incorrect pci_mem_start.
> >>
> >> Hi Yakui,
> >>
> >> What do you mean by the PCI0 _CRS being incorrect ? Why would the BIOS
> >> give a incorrect _CRS object ?
> >> Also we don't just take the value given from the _CRS method, we still
> >> read the e820_map to search for an unallocated resource. So even if
> >> (by chance) the _CRS method returns incorrect value we would still
> >> figure out if there is a collision with an already allocated resource.
> > In the patch the address obtained from the _CRS object will be passed
> > into the function of e820_search_gap. In such case maybe we will get the
> > pci_mem_start different with the e820_setup_gap.
>
> True..the whole idea behind doing this patch was to get a correct
> (different) value for pci_mem_start.
> We read the _CRS object over here to make sure that we assign the
> pci_mem_start from the address range which is reserved by the BIOS for
> PCI devices.
>
> Also this reading of _CRS object would be done before we start
> initializing the pci devices, i.e. before we start using the value of
> pci_mem_start, so the original value assigned by pci_setup_gap is just
> overwritten by this function. So that should be fine IMHO.
> Also we would still want the call for e820_setup_gap because there can
> be systems with no acpi support or acpi disabled
>
>
> >
> >> >
> >> > At the same time after the patch is applied, pci_mem_start will be
> >> > parsed in two different ways.
> >>
> >> Yes pci_mem_start would be initialized in 2 different ways but we
> >> still have to parse the e820_map the old way because there could be
> >> systems without ACPI.
> >>
> >> > If the result is different, maybe the
> >> > incorrect pci_mem_start will be used.
> >>
> >> Yeah, The result is different in my case. Though my BIOS reserves
> >> hotpluggable memory region, kernel doesn't respect that right now and
> >> just parses the e820_map to calculate the gap and pci_mem_start value.
> >> I have explained the problem in this mail.
> >>
> >>
http://marc.info/?l=linux-acpi&m=121391675711763&w=2
> >>
> >> Maybe nobody has seen this problem yet, because there are no systems
> >> out there with less than 4GB memory to start with and which allow
> >> memory hotplug.
> >>
> >> But still i don't understand what do you mean by, we can get incorrect
> >> pci_mem_start, in which case ?
> >
> > In the function of setup_arch the pci_mem_start will be parsed by
> > searching the e820 table. After the patch is applied, we will parse the
> > pci_mem_start again in the function of pci_acpi_scan_init and it will
> > override the value parsed in the function of setup_arch. If the
> > pci_mem_start is incorrect in the second case, maybe it will have side
> > effect.
>
> Yes it will override. But how can the value be incorrect in the second
> case. As explained in my previous mail we still parse the e820_map to
> check if we have unclaimed resources between start_address (that read
> from _CRS) to 2^32. So even if this start_address is wrong we would
> catch that during parsing e820_map. But again why would the _CRS
> return incorrect values, are you talking about errors in BIOS ?
