From owner-freebsd-arch@FreeBSD.ORG Fri Jan 30 20:31:45 2015 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id AC15F461 for ; Fri, 30 Jan 2015 20:31:45 +0000 (UTC) Received: from bigwig.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 845E933F for ; Fri, 30 Jan 2015 20:31:45 +0000 (UTC) Received: from ralph.baldwin.cx (pool-173-54-116-245.nwrknj.fios.verizon.net [173.54.116.245]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id A0E5CB913; Fri, 30 Jan 2015 15:31:44 -0500 (EST) From: John Baldwin To: Konstantin Belousov Subject: Re: Wrapper API for static bus_dma allocations Date: Fri, 30 Jan 2015 15:31:23 -0500 Message-ID: <1440008.gcoNUU8dV6@ralph.baldwin.cx> User-Agent: KMail/4.14.2 (FreeBSD/10.1-STABLE; KDE/4.14.2; amd64; ; ) In-Reply-To: <20150130152150.GX42409@kib.kiev.ua> References: <2800970.jY4xzTy9Hz@ralph.baldwin.cx> <54CB9B9F.50905@FreeBSD.org> <20150130152150.GX42409@kib.kiev.ua> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Fri, 30 Jan 2015 15:31:44 -0500 (EST) Cc: Poul-Henning Kamp , 'freebsd-arch' X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 30 Jan 2015 20:31:45 -0000 On Friday, January 30, 2015 05:21:50 PM Konstantin Belousov wrote: > 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. Yes, it is very annoying. I think some old ISA SCSI HBA driver might have used it to skip over some low-memory hole (i.e. there were two valid DMA ranges and this was the kludge instead of having two sets of lowaddr/highaddr exclusions). (That is one part of the API we could rototill is to just remove the highaddr arg just use a single arg which is effectively lowaddr. I think all drivers always set highaddr to BUS_SPACE_MAXADDR.) -- John Baldwin