On Fri, 01 Sep 2006 12:53:47 -0700 Roland Dreier <[EMAIL PROTECTED]> wrote:
> Roland> My understanding is that __raw_writeq() is like writeq() > Roland> except not strongly ordered and without the byte-swap on > Roland> big-endian architectures. The __raw_writeX() variants are > Roland> convenient to avoid having to write inefficient code like > Roland> writel(swab32(foo), ...) when talking to a PCI device that > Roland> wants big-endian data. Without the raw variant, you end > Roland> up with a double swap on big-endian architectures. > > Oh, I left one other thing out: writeq() and __raw_writeq() shold be > atomic in the sense that no other transactions should be able to get > onto the IO bus in the middle -- so implementing writeq() as two > writel()s in a row is not allowed > > Andrew> OK. Can we please stop hacking around this in drivers and > > Andrew> a) work out what it's supposed to do > > Andrew> b) document that (Documentation/DocBook/deviceiobook.tmpl > Andrew> or code comment or whatever) > > Andrew> c) tell arch maintainers? > > Yes, I agree that's a good plan, especially the documentation part. > However I would argue that what's in > drivers/infiniband/hw/mthca/mthca_doorbell.h > is legitimate: the driver uses __raw_writeq() when it exists and uses > two __raw_writel()s properly serialized with a device-specific lock to > get exactly the atomicity it needs on 32-bit archs. No, driver-specific workarounds are not legitimate, sorry. The driver should simply fail to compile on architectures which do not implement __raw_writeq(). We can speed up the process by sending helpful emails to architecture maintainers, but they'll notice either way. Let's fix it once, and in the correct place. > It's an open question what drivers that don't actually need atomicity > but just want a convenient way to write 64 bits at time should do. Well yeah. We should sort out the design issues before implementing things ;) _______________________________________________ openib-general mailing list [email protected] http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
