Date: Fri, 30 Jan 2015 17:21:50 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: John Baldwin <jhb@FreeBSD.org> Cc: Poul-Henning Kamp <phk@phk.freebsd.dk>, 'freebsd-arch' <freebsd-arch@freebsd.org> Subject: Re: Wrapper API for static bus_dma allocations Message-ID: <20150130152150.GX42409@kib.kiev.ua> In-Reply-To: <54CB9B9F.50905@FreeBSD.org> References: <2800970.jY4xzTy9Hz@ralph.baldwin.cx> <67604.1422568494@critter.freebsd.dk> <54CB9B9F.50905@FreeBSD.org>
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On Fri, Jan 30, 2015 at 09:56:31AM -0500, John Baldwin wrote: > On 1/29/15 4:54 PM, Poul-Henning Kamp wrote: > > -------- > > In message <2800970.jY4xzTy9Hz@ralph.baldwin.cx>, John Baldwin writes: > > > >> The bus_dma API to allocate a chunk of static DMA'able memory (e.g. for > >> descriptor rings) can be a bit obtuse [...] > > > > Isn't it time we take a good hard stare at all of the bus_dma API, > > and refactor it into something a lot more compact ? > > Given the amount of oddball hardware out there I don't think there is a > lot you can cut out. The filter function might be something we can lose > (and losing it would simplify the implementation), but all the other > weird constraints are actually used by something AFAIK. I do think we > can provide some simpler wrappers for some of the more common cases, but > there will be some hardware for which those wrappers do not work. > > One suggestion Scott has had is to at least make it easier to extend the > API by using getter/setter routines on the tag to work with tag > attributes instead of passing them all in bus_dma_tag_create(). BTW, filter function is useless. It can deny specific bus address from being used, but it does not provide the busdma implementation even a hint what other address should be (tried to) used. In dmar busdma, I simply ignored it. And there is no real users of filter in the tree.
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