Date: Sat, 25 Apr 2015 21:18:46 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Jason Harmening <jason.harmening@gmail.com> Cc: Svatopluk Kraus <onwahe@gmail.com>, FreeBSD Arch <freebsd-arch@freebsd.org> Subject: Re: bus_dmamap_sync() for bounced client buffers from user address space Message-ID: <20150425181846.GN2390@kib.kiev.ua> In-Reply-To: <553BD501.4010109@gmail.com> References: <CAFHCsPXMjge84AR2cR8KXMXWP4kH2YvuV_uqtPKUvn5C3ygknw@mail.gmail.com> <CAM=8qan-4SbKJaddrfkv=HG3n%2BHaOPDL5MEPS9DoaTvnhrJPZQ@mail.gmail.com> <20150425094152.GE2390@kib.kiev.ua> <553B9E64.8030907@gmail.com> <20150425163444.GL2390@kib.kiev.ua> <553BC9D1.1070502@gmail.com> <20150425172833.GM2390@kib.kiev.ua> <553BD501.4010109@gmail.com>
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On Sat, Apr 25, 2015 at 12:55:13PM -0500, Jason Harmening wrote: > Ah, that looks much better. A few things though: > 1) _bus_dmamap_load_ma (note the underscore) is still part of the MI/MD > interface, which we tell drivers not to use. It looks like it's > implemented for every arch though. Should there be a public and > documented bus_dmamap_load_ma ? Might be yes. But at least one consumer of the KPI must appear before the facility is introduced. > 2) There is a bus_dmamap_load_ma_triv that's part of the MI interface, > but it's not documented, and it seems like it would be suboptimal in > certain cases, such as when dmar is enabled. When DMAR is enabled, bus_dmamap_load_triv() should not be used. It should not be used directly even when not. Drivers should use bus_dmamap_load_ma(), and implementation redirects to _triv() if needed. The _triv() is the helper to allow bus_dmamap_load_ma() to exists on architectures which cannot implement, on not yet implemented, proper page array load op. > 3) Using bus_dmamap_load_ma would mean always using physcopy for bounce > buffers...seems like the sfbufs would slow things down ? For amd64, sfbufs are nop, due to the direct map. But, I doubt that we can combine bounce buffers and performance in the single sentence.
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