Messages in this thread | | | Date | Thu, 15 Jul 2010 18:46:58 +0200 (CEST) | From | Unai Uribarri <> | Subject | Re: Workaround hardware bug addressing physical memory |
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----- "Marin Mitov" <mitov@issp.bas.bg> wrote:
| On 15.7.2010, Unai Uribarri wrote: | > Thanks. | > ----- "Marin Mitov" <mitov@issp.bas.bg> wrote: | > | > | On Wednesday, July 14, 2010 08:06:49 pm you wrote: | > | > ----- "Marin Mitov" <mitov@issp.bas.bg> wrote: | > | > | > | > | Hi, | > | > | | > | > | This is pci driver. You can set dma mask: | > | > | | > | > | dma_set_coheren_mask(pdev, DMA_BIT_MASK(31)) | > | > | | > | > | All further alloc_coherent() should be from the region 0-2GB. | > | > | | > | > | > | > But I'm using a 64 bit operating system with 32GB of RAM. It's | a | > | > pity to be unable to use 4GB-32GB range because the 2-4GB range | is | > | > unusable. So I've written this code to skip invalid areas. Do | you | > | > think this code could be useful for other drivers? | > | | > | Let me summarize if I have correctly understood what you do. | > | | > | First, your hardware has problems when the physical (bus) address | > | is out of the 0-2GB region, so you cannot use buffers that are out | | > | of this range in any case. And the defect is in the peripheral, | not in | > | the bridge between it and the memory. | > | > The hardware works correctly for physical address in the ranges 0 to | 2GB | > AND 4GB to 32GB. Physical address in the 2-4GB range are read | correctly | > by the device. But when the device tries to write to them it issues | | > invalid PCIe transaction headers: it tries to access such addresses | using | > a 64-bit transactions when the PCI Express standard mandates to use | 32-bit | > transactions for memory addresses below 4GB. Some bridges accept | such | > invalid transactions, but Intel 5500 chipset rejects them. | > | > I'm allocating 256MB of RAM for I/O buffers; I'm fear that | restricting all | > the allocations to the first 2GB of memory will put too much | pressure in | > that zone of memory. But restricting it to 4GB and above will be | okay. | > | > Is there any way to restrict to memory address above 4GB? | | Would this work for you? | From: Documentation/kernel-parameters.txt: | | memmap=nn[KMG]$ss[KMG] | [KNL,ACPI] Mark specific memory as reserved. | Region of memory to be used, from ss to ss+nn. | Example: Exclude memory from 0x18690000-0x1869ffff | memmap=64K$0x18690000 | or | memmap=0x10000$0x18690000
I think that linking in a list the unusable memory and freeing it after completing all the allocations is a better solution.
Thanks.
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