Date: Sat, 20 Mar 2004 12:04:37 -0800 From: Marcel Moolenaar <marcel@xcllnt.net> To: "M. Warner Losh" <imp@bsdimp.com> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/conf files src/sys/dev/uart uart_cpu.h uart_cpu_alpha.c uart_cpu_amd64.c uart_cpu_i386.c uart_cpu_ia64.c uart_cpu_pc98.c uart_cpu_sparc64.c uart_subr.c Message-ID: <20040320200437.GB84959@dhcp01.pn.xcllnt.net> In-Reply-To: <20040320.104521.08405415.imp@bsdimp.com> References: <200403200214.i2K2E3ps052217@repoman.freebsd.org> <20040320080027.GC567@funkthat.com> <20040320085431.GA74398@dhcp01.pn.xcllnt.net> <20040320.104521.08405415.imp@bsdimp.com>
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On Sat, Mar 20, 2004 at 10:45:21AM -0800, M. Warner Losh wrote: > In message: <20040320085431.GA74398@dhcp01.pn.xcllnt.net> > Marcel Moolenaar <marcel@xcllnt.net> writes: > : Probe order is irrelevant if you specify the device by its I/O port > : or memory mapped I/O address. > > Only for devices that have fixed addresses. This wouldn't be true for > devices on the PCI bus, where probe order could affect the resources > assigned to a given device. The only real way for self-enumearting > busses are a bus-specific address. Devices that don't have a fixed address cannot be used as low-level console as there's no way we can know where the device is. Unless of course the device is pinned somewhere in advance. But this obviously must happen before we enter the kernel, which for all practical purposes and our point of view means that the device has a fixed address. Hence, we don't have to deal with devices that don't have a fixed address. Alternatively, if the platform has some form of indirection (like sparc64 and powerpc that can look up device names in the OpenFirmware device tree) you don't want to use addresses, you want to use the indirection. Nonetheless, the indirection (e.g. name or alias) has to be fixed and known up front so that we have something fixed to do the lookup with. The lookup may yield a different result across reboots. Lastly, if the platform provides the information in some form (like the HCDP table on DIG64 compliant machines), we use that and not the environment variables. This is related to the indirect lookup mentioned above. -- Marcel Moolenaar USPA: A-39004 marcel@xcllnt.net
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