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Date: Wed, 25 Jun 2008 13:39:25 +0800 From: Zhao Yakui <yakui.zhao@...el.com> To: Alok kataria <alokkataria1@...il.com> Cc: akataria@...are.com, lenb@...nel.org, Ingo Molnar <mingo@...e.hu>, linux-acpi <linux-acpi@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 2/2] acpi based pci gap caluculation v2 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@...el.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. > > > > 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. Thanks. Yakui. > Thanks, > Alok > > > > Best regards. > > Yakui > >> > >> > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux-acpi" in > >> the body of a message to majordomo@...r.kernel.org > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > the body of a message to majordomo@...r.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > Please read the FAQ at http://www.tux.org/lkml/ > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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