Date: Thu, 19 Mar 2015 13:56:43 -0600 From: Ian Lepore <ian@freebsd.org> To: Warner Losh <imp@bsdimp.com> Cc: freebsd-arm@freebsd.org, =?ISO-8859-1?Q?Mat=EDas?= Perret Cantoni <perretcantonim@gmail.com> Subject: Re: Zynq-7020 SoC on-chip-memory Message-ID: <1426795003.87786.3.camel@freebsd.org> In-Reply-To: <91283C43-66EA-4CE7-B080-D5F4223A725B@bsdimp.com> References: <CADLKG01oSQ=caZFOnZQM14=pAVPvLz45EznMes9mVfG2kD6TEQ@mail.gmail.com> <D2F57338-AC51-4A2D-982B-F024A5E422E4@sbcglobal.net> <91283C43-66EA-4CE7-B080-D5F4223A725B@bsdimp.com>
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On Thu, 2015-03-19 at 13:38 -0600, Warner Losh wrote: > > On Mar 19, 2015, at 1:19 PM, Thomas Skibo <ThomasSkibo@sbcglobal.net>= wrote: > >> Any advice on how to add this memory to my system? > >=20 > > I think it might be more trouble than it=92s worth. >=20 > I do too. I tried back in the day to map Atmel=92s small cache of RAM i= nto the OS > as well. It didn=92t go well. >=20 > You likely don=92t want to use this 256kB for general purpose memory an= yway. You=92ll > likely want to use it for something special. For Atmel, I was looking a= t running interrupt > handlers and/or ethernet packets through that memory=85 There were issu= es with doing > either one of these that I can no longer recall... >=20 > Warner >=20 My vague plan for a long time has been to try to get L1 page descriptor tables into this sort of ram. Often the on-chip ram can be accessed at the same speed as L1 cache so it would be a big win. Sometimes when a SoC has on-chip crypto accellerator hardware, this on-chip ram (or some portion of it) needs to be dedicated to it. If it's described in the memory region data in FDT it'll just get handed over to the vm subsystem as available memory, and get allocated for who-knows-what. -- Ian
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