On Tue, 2008-06-24 at 23:04 -0700, Alok kataria wrote: > Hi Yakui, > > On Tue, Jun 24, 2008 at 10:39 PM, Zhao Yakui <yakui.zhao@xxxxxxxxx> 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@xxxxxxxxx> 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 ? The pci_mem_start is still gotten by parsing the E820 table.But the input parameter start_addr will be used in the function of e820_search_gap. If the following is the resource start address returned by the PCI0 _CRS object , maybe the different pci_mem_start will be gotten. 0xE0000000 0xE4000000 At the same time if several start address is returned by the _CRS object, the e820 table will be parsed several times. Thanks. Yakui > Thanks, > Alok -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
