On Tue, Sep 29, 2020 at 1:29 PM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > > On Tue, Sep 29, 2020 at 8:44 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > > On Tue, Sep 29, 2020 at 7:49 PM Peter Collingbourne <pcc@xxxxxxxxxx> wrote: > > > But aside from all this, why is this blocking the migration from fbdev > > to drm? With fbdev you don't have buffer allocations, nor dma-buf > > support, and somehow android can boot. > > I do not know how Android does things these days but back in the > days it would request a virtual framebuffer twice the height of the > physical framebuffer and then pan that up/down between composing > frames, thus achieving a type of double-buffering from userspace. > > Given the type of bugs Peter is seeing this seems to still be the > case, Peter can you confirm? This is what the userspace fbdev driver does (or at least tries to do). If this operation fails (as it does with the old fbdev CLCD driver) the driver falls back to using a single buffer. The DRM driver doesn't do anything like that, it allocates multiple buffers. IIRC that fails on stock kernels but with an increase to the amount of video RAM declared in the DTS (e.g. [1]) that operation turns out to succeed. Peter [1] https://www.spinics.net/lists/arm-kernel/msg800628.html _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
