From mboxrd@z Thu Jan 1 00:00:00 1970 In-Reply-To: Date: Tue, 8 Feb 2000 15:56:37 +0100 To: Gabriel Paubert CC: linuxppc-dev@lists.linuxppc.org, linux-fbdev@vuser.vu.union.edu From: Benjamin Herrenschmidt Subject: Re: [linux-fbdev] Retrace Message-Id: <20000208155637.001939@mailhost.mipsys.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linuxppc-dev@lists.linuxppc.org List-Id: On Tue, Feb 8, 2000, Gabriel Paubert wrote: >On x86 you have /dev/port which is disabled on PPC. I once or twice >suggested (but was greeted with a deafening silence) that we could >resurrect it and add an mmap method so that privileged programs may access >I/O ports with: > > io_fd= open("/dev/port", O_RDWR); > iobase=mmap(0, device_size, PROT_READ|PROT_WRITE, MAP_SHARED, > io_fd, device_base); > > >> Unfortunately, with weird host bridges like Apple Uni-N (that has 3 >> busses with 3 different io bases but the same bus number), it's almost >> impossible to get it correct, or eventually by parsing /proc/device-tree. > >Not a problem if device_base is unique, you have to check that >device_base+device_size fits within one area. It must be unique at one >point to distinguish them from the processor perspective. device_base may not be unique. Actually, that depends what is device_base and how it's retreived. But for example, reading the BARs can give you identical io base for devices on different sub-bridges, the distinction beeing done by the iobase of the bridge itself. The fact is that macos don't care, since it's completely based on the device-tree, MacOS-drivers call in/out functions that use the base address of the parent bridge. I have in mind the possibility of defining fake bridges in the kernel to work around the Uni-N problem as a whole, but this leads to a bunch of other problems (like desynchro with the device-tree, which can be annoying for other things) and I'm not familiar enough with 2.3.x PCI layer yet. What's the usual method used by X-like apps to get the base of a device ? /proc/pci ? We could also have /proc/pci export "fixed" bases that already take into account the iobase of the bridge. We are in a realm where I lack experience with Linux to be able to tell which solution is better (and have more chances of beeing accepted ;) ** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/