Date: Tue, 18 Jun 2013 13:30:34 +0200 From: Niclas Zeising <zeising@freebsd.org> To: Marius Strobl <marius@alchemy.franken.de> Cc: arch@freebsd.org Subject: Re: Bus space routines Message-ID: <51C044DA.8030406@freebsd.org> In-Reply-To: <20130618111351.GA43938@alchemy.franken.de> References: <51C0345E.4000309@freebsd.org> <20130618111351.GA43938@alchemy.franken.de>
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On 2013-06-18 13:13, Marius Strobl wrote: > On Tue, Jun 18, 2013 at 12:20:14PM +0200, Niclas Zeising wrote: >> This has been discussed before [1], but there seem to still be a lack of >> consensus, so I'll ask again. >> >> Should in*/out* macros or bus_space* functions be used in userland code? >> The background is that the port devel/libpciaccess uses these routines >> on FreeBSD. In a first incarnation it used the bus_space* routines, see >> this patch: >> >> http://trillian.chruetertee.ch/ports/browser/trunk/devel/libpciaccess/files/patch-src-freebsd_pci.c?rev=591 >> >> This was later changed to use the in*/out* macros directly, with the >> motivation that the bus_space* functions is a KPI that shouldn't be used >> in userland. See following for an updated patch: >> >> http://trillian.chruetertee.ch/ports/browser/trunk/devel/libpciaccess/files/patch-src-freebsd_pci.c?rev=815 >> >> The problem is that the in*/out* macros differ between FreeBSD and >> Debian/kFreeBSD, and Debian/kFreeBSD want to switch back to use >> bus_space* again. >> >> My question is simply, which one is correct, or should libpciaccess be >> reworked in a completely different way? > > The latter; in*/out*() are somewhat okay if you want to restrict this > to work on x86 without PCI domains only. The above approach to using > bus_space(9) is one big hack, though. The right way for employing that > API is to allocate the corresponding bus resource of a particular device > and then to obtain bus tag and handle via rman_get_bus{tag,handle}(9) - > which won't work from userland, however. The shortcut to just stick in > {AMD64,I386}_BUS_SPACE_IO instead is totally unportable as generally > a bus tag isn't a mere constant and also may depend on which PCI bus > and domain a particular device is located on/in. > What we really need is a proper interface allowing userland to access > PCI I/O and memory registers, f. e. via /dev/pci, and for libpciaccess > to build upon that, i. e. essentially the same as things work on/with > Linux and /sys/bus/pci/device. As a side-effect this then also permits > to properly sanity check PCI accesses from userland within the kernel. > > Marius > That is true, however, it won't build itself today, and we need to have this working in the meantime, so what do you suggest we use for now? Also, as a side note, how hard would it be to implement this API, do you think? Is it something a junior hacker (that is, me) can do? Regards! -- Niclas
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