On Tue, Jul 9, 2013 at 2:18 PM, James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: > On Tue, 2013-07-09 at 14:39 -0600, Myron Stowe wrote: >> Is the "megaraid" driver still actively used and maintained? I originally >> posted this series on 06.07.2013 and after receiving no comments, pinged >> the list again on 06.17.2013 and still received no comments/feedback. >> >> Trying again as I believe there is a real issue here, which I'd like >> confirmation on, and we really should remove the local copy/usage of >> 'struct pci_dev' that this driver currently maintains. >> >> >> While the megaraid device itself may be 64-bit DMA capable, 32-bit address >> restricted DMA buffers are apparently required for "internal commands" as >> is denoted by a couple of comments - "For all internal commands, the >> buffer must be allocated in <4GB address range" - within the driver. >> >> If the device is 64-bit DMA capable then, once it is setup, any subsequent >> DMA allocations for "internal commands" would not be properly restricted >> due to megaraid_probe_one() having called pci_set_dma_mask() on pdev with >> DMA_BIT_MASK(64). The driver attempts to solve this by using >> make_local_pdev() to dynamically create local pci_dev structures which are >> then set and used for allocating 32-bit address space restricted DMA >> buffers[1] but I don't believe that the implementation works as intended. >> >> >> Assume that the megaraid device is 64-bit DMA capable. While probing the >> device and attaching the megaraid driver, pci_set_dma_mask() is called >> with the "originating pdev" and a DMA_BIT_MASK of 64. As a result, any >> subsequent dynamic DMA related allocations associated with the >> "originating pdev" will acquire 64-bit based buffers, which do not meet >> the addressing restrictions for internal commands. >> >> megaraid_probe_one(struct pci_dev *pdev, ...) >> ... >> pci_set_dma_mask(pdev, DMA_BIT_MASK(64)); >> >> As mentioned, the driver attempts to solve this by using make_local_pdev() >> to dynamically create local pci_dev structures - "local pdev's" - which >> are set with a DMA_BIT_MASK of 32. >> >> make_local_pdev >> alloc_pci_dev >> memcpy >> pci_set_dma_mask >> dma_set_mask >> *dev->dma_mask = mask; >> >> The "local pdev" is then used in allocating a DMA buffer in an attempt to >> meet the < 4 GB restriction. >> >> For a 64-bit DMA capable device, the "originating pdev" will have its >> 'dma_mask' set to 0xffffffffffffffff after the driver attaches. >> Subsequently, when an internal command is initiated, make_local_pdev() is >> called. make_local_pdev() uses the PCI's core to allocate a "local pdev" >> and then copies the "originating pdev" content into the newly allocated >> "local pdev". As a result of copying the "originating pdev" content into >> the "local pdev", pdev->dev.dma_mask will be pointing back to the >> "originating pdev's" 'dma_mask' member, not the "local pdev's" as >> intended. Thus, when make_local_pdev() calls pci_set_dma_mask() in an >> attempt to set the "local pdev's" DMA mask to 32 it will instead overwrite >> the "originating pdev's" DMA mask. Thus, after any user initiated >> commands are issued, all subsequent DMA allocations will be 32-bit >> restricted from that point onward regardless of whether they are internal >> commands or otherwise. >> >> >> This patch fixes the issue by removing the setup of DMA_BIT_MASK to 64 in >> megaraid_probe_one(), leaving the driver with default 32-bit DMA >> capabilities, as it currently ends up in such a state anyway after any >> internal commands are initiated. >> >> >> [1] It seems strange that both mega_buffer/buf_dma_handle and >> make_local_pdev() both exist for internal commands but this has been >> the case for a long time - at least since 2.6.12-rc2. Perhaps there >> is some coalescing that could be done. >> --- >> Myron Stowe (3): >> [SCSI] megaraid: Remove 64-bit DMA related dead code >> [SCSI] megaraid: Remove local pdev's >> [SCSI] megaraid: Remove 64-bit DMA_BIT_MASK capability > > Adam, you do drive by coding on this for LSI ... ack or reject, please. > > James > > James, I have just now located my box of MegaRAID Parallel SCSI controllers. I will review and test the patch series from Myron and respond by next Monday. -Adam -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
