Date: Mon, 8 Nov 2004 15:53:38 -0800 From: "Vinod Kashyap" <vkashyap@amcc.com> To: "James R. Van Artsalen" <james@jrv.org> Cc: freebsd-amd64@freebsd.org Subject: RE: How to debug >2GB memory issues (and 3ware) Message-ID: <I6VX1N00.LM8@hadar.amcc.com>
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> -----Original Message----- > From: James R. Van Artsalen [mailto:james@jrv.org] > Sent: Monday, November 08, 2004 3:42 PM > To: Vinod Kashyap > Cc: Michael R. Wayne; freebsd-amd64@freebsd.org > Subject: Re: How to debug >2GB memory issues (and 3ware) > > > Vinod Kashyap wrote: > > >The 3ware driver (twe) for 7xxx/8xxx controllers can handle upto > >4 GB memory on FreeBSD 4.x, and beyond 4 GB on FreeBSD 5.x. The > >driver (twa) for 9xxx controllers can handle memory beyond 4 GB > >on both 4.x and 5.x. > > > > > > The twe driver in MAIN seems to be limited to direct access > to the lower > 4GB. Am I misinterpreting the significance of this code in > twe_freebsd.c? > > /* > * Allocate the parent bus DMA tag appropriate for PCI. > */ > if (bus_dma_tag_create(NULL, > /* parent */ > 1, 0, > /* alignment, boundary */ > BUS_SPACE_MAXADDR_32BIT, > /* lowaddr */ > BUS_SPACE_MAXADDR, > /* highaddr */ > NULL, NULL, > /* filter, filterarg */ > MAXBSIZE, TWE_MAX_SGL_LENGTH, > /* maxsize, nsegments */ > BUS_SPACE_MAXSIZE_32BIT, > /* maxsegsize */ > BUS_DMA_ALLOCNOW, > /* flags */ > NULL, > /* lockfunc */ > NULL, > /* lockarg */ > > What this piece of code does is, it lets busdma know that the driver cannot be passed addresses beyond 4 GB. So, busdma maps any addresses beyond 4 GB to the range (< 4 GB) requested by the driver, and so, the driver is effectively able to "handle" more than 4 GB memory. All this because the underlying controller cannot access > 4 GB addresses. The 9xxx controllers, however, can access > 4 GB addresses, and so, the driver does not request for a smaller range of addresses.home | help
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