* Alan Cox wrote: > On Wed, 11 Apr 2012 14:10:26 +0200 > Thierry Reding <thierry.reding@xxxxxxxxxxxxxxxxx> wrote: > > > This series adds a basic DRM driver for NVIDIA Tegra 2 processors. It > > currently only supports the RGB output and I've successfully tested it > > against the fbcon kernel module and the xf86-video-modesetting driver. > > The code uses the Tegra's IOMMU/GART to remap non-contiguous memory. > > This means that currently video memory is limited to 32 MB, the size of > > the GART aperture. > > You should only need continguous memory with GEM for the framebuffer / > console bits via /dev/fb. In theory the fb layer can be taught to hanndle > non linear framebuffers but nobody has yet done so. (Now there's a GSOC > project ... ;)) > > What we do on GMA500 is to allocate the kernel framebuffer from linearly > mapped memory but the normal GEM objects from anywhere as the GEM mapping > into userspace will deal with presenting it to user space as a virtually > linear buffer. That's actually what the driver does as well. It uses the shmfs-backed memory provided by GEM and only maps it through the GART to provide a linear view for the display controller which cannot do scatter-gather I/O. Neither the kernel nor the user-space mapping go through the GART. You are right that for anything but the framebuffer objects it probably doesn't matter. It's a little hard to tell because I don't have any documentation for either the 2D nor 3D engines. Eventually a better option might be to use stolen memory instead of remapping it through the GART. Thierry
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