On May 7, 2012, at 9:27 AM, John Baldwin wrote: > On Friday, May 04, 2012 5:25:32 pm Warner Losh wrote: >> >> On May 4, 2012, at 1:41 PM, Hans Petter Selasky wrote: >> >>> On Friday 04 May 2012 19:18:56 Warner Losh wrote: >>>> On May 4, 2012, at 10:26 AM, Hans Petter Selasky wrote: >>>>> On Friday 04 May 2012 18:14:16 John Baldwin wrote: >>>>>> On Friday, May 04, 2012 11:38:47 am Hans Petter Selasky wrote: >>>>>>> Author: hselasky >>>>>>> Date: Fri May 4 15:38:47 2012 >>>>>>> New Revision: 235007 >>>>>>> URL: http://svn.freebsd.org/changeset/base/235007 >>>>>>> >>>>>>> Log: >>>>>>> MFC r233662, r233677 and r233678: >>>>>>> >>>>>>> Writing zero to BAR actually does not disable it and >>>>>>> it is even harmful as hselasky found out. Historically, >>>>>>> this code was originated from (OLDCARD) CardBus driver and later >>>>>>> leaked into PCI driver when CardBus was newbus'ified and refactored >>>>>>> with PCI driver. However, it is not really necessary even for >>>>>>> CardBus. >>>>>> >>>>>> FYI, I've got one bug report on HEAD where these changes broke a >>>>>> machine's ATA controller. >>>>> >>>>> Have you considered adding code to disable the I/O or memory range >>>>> instead of writing 0 to the bar in this case? >>>> >>>> I tried that once upon a time, but was problematical with some bridges > that >>>> had BARs at non-standard locations that needed the I/O or MEM bit set in >>>> order to work... >>>> >>>> Warner >>> >>> If the size of the bar is a few megabytes, then moving it to location 0 is >>> definitely wrong. Else it might work! >> >> Only if the bridge passes the transactions for that memory to the PCI bus > for decoding. The reason it worked for as long as it did was that we had > bridges that passed the memory cycles to DRAM for addresses near 0 and they > didn't make it onto the PCI bus. Except in embedded systems, I fail to see > how that could have changed in the interim. The physical layout of x86 has > actual memory at location 0 and it would be a big performance hit to push > those transactions onto the pci bus, so nobody in their right mind would do > that. > > Not true. During NEW_PCIB testing I at one point fat-fingered something such > that I had an memory window on a PCI-PCI bridge claim address 0 and the boot > promptly hung as soon as that register was written.
I'll grant that for bridges... The code in question just does devices though... Still, something we should avoid... Warner _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
