Date: Mon, 27 Aug 2012 07:38:06 -0600 From: Warner Losh <imp@bsdimp.com> To: Hans Petter Selasky <hans.petter.selasky@bitfrost.no> Cc: freebsd-arm@freebsd.org, freebsd-mips@freebsd.org, freebsd-arch@freebsd.org Subject: Re: Partial cacheline flush problems on ARM and MIPS Message-ID: <A749E691-BF25-4B72-B929-56ABEB10F3E9@bsdimp.com> In-Reply-To: <zarafa.503b0e81.5c36.1a2f71091ebf9bd2@eric2.bitfrost> References: <6D83AF9D-577B-4C83-84B7-C4E3B32695FC@bsdimp.com> <zarafa.503b0e81.5c36.1a2f71091ebf9bd2@eric2.bitfrost>
next in thread | previous in thread | raw e-mail | index | archive | help
On Aug 27, 2012, at 12:06 AM, Hans Petter Selasky wrote: > Hi, > Correct. >=20 > > We also need some rules about working with buffers obtained from > > bus_dmamem_alloc() and external buffers passed to bus_dmamap_load(). = I > > think the rule should be that a buffer obtained from = bus_dmamem_alloc(), > > or more formally any region of memory mapped by a bus_dmamap_load(), = is > > a single logical object which can only be accessed by one entity at = a > > time. That means that there cannot be two concurrent DMA operations > > happening in different regions of the same buffer, nor can DMA and = CPU > > access be happening concurrently even if in different parts of the > > buffer. =20 >=20 > Is this something which we can fix using a simple = __align(USB_DMA_ALIGN) on elements in C-structures which are allowed to = be DMA loaded. No. I don't think so. the reason is that you can't define USB_DMA_ALGIN = to be a constant on MIPS, at least, or I think ARM because that's = determined at run time. > Also: Why is busdma not complaining when loading a non-valid buffer = pointer? Speed and code simplicity. Warner
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?A749E691-BF25-4B72-B929-56ABEB10F3E9>