Messages in this thread | | | Date | Thu, 28 Apr 2005 17:38:28 -0600 | From | Grant Grundler <> | Subject | Re: pci-sysfs resource mmap broken (and PATCH) |
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On Fri, Apr 29, 2005 at 08:47:27AM +1000, Benjamin Herrenschmidt wrote: > > Well, if it's a device driver decision, I guess that's ok. > > And the primary device driver happens to live in user space in X.org case. > > Agreed, but 1) Do you have an idea on how to expose this capability with > the sysfs interface ? Adding ioctl's to it would suck big time :) and
I don't know enough about VM/TLB stuff to know the right answer.
I suspect the MAP_* attribute/hint needs to be passed in together with the mmap call if any arch (ia64?) would return a different virtual address depending the attribute (e.g cached vs uncached).
And write combining might be done in a "layer" below the CPU in the HW hierarchy. e.g. PCI Host bus controller might combine writes for some MMIO regions. I don't know if arch specific mmap support can figure out which HW is the right one to enable write combining in for a particular MMIO region or PCI device.
I generally don't work with graphics devices and only recently started poking at infiniband support (128-512MB BAR depending on card option) to understand really well how BAR is accessed/used.
> 2) It's still nice to have a "workaround" for existing X since the > performance benefit is significant, but then, it's in arch code, so > that's fine (and I could indeed limit it to VGA class devices as David > suggests).
Yup.
thanks, grant
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