Hi Am 09.04.19 um 09:12 schrieb kra...@redhat.com: > Hi, > >> If not for TTM, what would be the alternative? One VMA manager per >> memory region per device? > > Depends pretty much on the device. > > The cirrus is a display device with only 4 MB of vram. You can't fit > much in there. A single 1024x768 @ 24bpp framebuffer needs more 50% > of the video memory already. Which is why the cirrus driver (before the > rewrite) had to migrate buffers from/to vram on every page flip[1]. Which > is one[2] of the reasons why cirrus (after rewrite) doesn't ttm-manage the > vram any more. gem objects are managed with the shmem helpers instead > and the active framebuffer is blitted to vram. > > The qemu stdvga (bochs driver) has 16 MB vram by default and can be > configured to have up to 256 MB. Plenty of room even for multiple 4k > framebuffers if needed. So for the bochs driver all the ttm bo > migration logic is not needed, it could just store everything in vram. > > A set of drm_gem_vram_* helpers would do the job for bochs.
Thanks for clarifying. drm_gem_vram_* (and drm_vram_mm for Simple TTM) is probably a better name for the data structures. > I'd expect the same applies to the vbox driver. > > Dunno about the other drm drivers and the fbdev drivers you plan to > migrate over. The AST HW can support up to 512 MiB, but 32-64 MiB seems more realistic for a server. It's similar with mgag200 HW. The old fbdev-supported device are all somewhere in the range between cirrus and bochs. Some drivers would probably benefit from the cirrus approach, some could use VRAM directly. Best regards Thomas > > cheers, > Gerd > > [1] Note: The page-flip migration logic is present in some of the other > drivers too, not sure whenever they actually need that due to being low > on vram too or whenever they just copied the old cirrus code ... > > [2] The other reason is that this allow to convert formats at blit time, > which helps to deal with some cirrus hardware limitations. > -- Thomas Zimmermann Graphics Driver Developer SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany GF: Felix Imendörffer, Mary Higgins, Sri Rasiah HRB 21284 (AG Nürnberg)
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