On Tuesday 15 December 2009 06:23:15 pm Huang Ying wrote: > On Wed, 2009-12-16 at 01:47 +0800, Bjorn Helgaas wrote: > > On Monday 14 December 2009 06:04:13 pm Huang Ying wrote: > > > On Sat, 2009-12-12 at 01:36 +0800, Bjorn Helgaas wrote: > > > > I think your code would be simpler if acpi_pre_map_gar() returned a > > > > struct acpi_iomap pointer (from the caller's point of view, this would > > > > be an opaque cookie). Then you could just supply that cookie to > > > > acpi_atomic_write(), and you wouldn't have to look it up again. Maybe > > > > you could even get rid of the list and all the fancy RCU & kref stuff > > > > then, too. > > > > > > The interface chosen is based on usage model, which is: > > > > > > 1. In init function, all GARs needed are pre-mapped > > > 2. In atomic context, pre-mapped GARs are accessed > > > 3. In exit function, all GARs are post-unmapped > > > > > > In 3), if struct acpi_iomap* is used as parameter for post-unmap > > > function, we need to record that pointer in another list. In 2), we need > > > find mapped address from GAR. > > > > I understand that my proposal would require a slight change in your > > usage model. I am suggesting that you make it follow the same pattern > > as pci_iomap(), e.g.: > > > > void *pci_iomap(struct pci_dev *, int bar, unsigned long len); > > unsigned int ioread32(void *); > > void pci_iounmap(struct pci_dev *, void *); > > > > void *acpi_map_generic_address(struct acpi_generic_address *); > > u64 acpi_read_atomic(void *); > > void acpi_unmap_generic_address(void *); > > > > acpi_map_generic_address() would validate the GAR and do the ioremap(). > > If the validation or ioremap() failed, it would return a NULL pointer. > > > > This would require the caller of acpi_map_generic_address() to hang onto > > the pointer returned (just as callers of pci_iomap() must hang onto the > > pointer it returns). > > > > The pointer would be supplied to acpi_read_atomic(), so it would not > > need to do acpi_check_gar() because we know it was done successfully > > in acpi_map_generic_address(). It wouldn't need to look up the GAR > > in the list because the list entry was passed in. Since all the > > possible failure conditions were checked in acpi_map_generic_address(), > > acpi_read_atomic() doesn't need to return status and could simply > > return the u64 directly. > > The usage model is different. Please take a look at > __apei_exec_read_register(). We need to get virtual address from > physical address in GAR. And many small-size GARs in ERST or EINJ may > share same page, so some kind of virtual space optimization is > necessary. The sharing could be done with a reference count in the map/unmap path. I don't have time to fully understand your patch series, but I suspect the issue is that you're interpreting opcodes, and those contain or reference generic_address structures, and you think it's easier just pass around the GAR pointer than it is to remember a (GAR, mapped-GAR) association made by pre_map_gar() and use the mapped-GAR when executing the "read" opcode. Bjorn -- 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
