The virtual size must be at least the size of the physical display. One approach toward double-buffering is to make the virtual height twice the physical height. To "flip" the displays you simply change the start of the visible view port.
See these: https://lb.raspberrypi.org/forums/viewtopic.php?t=47329 https://www.raspberrypi.org/forums/viewtopic.php?f=67&t=19073&p=324866#p324866 -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1777672 Title: QEMU aarch64 virtual/physical frame buffer Status in QEMU: New Bug description: I fully recognize that the error here could be mine, but the code is pretty simple and straightforward; When emulating a Raspberry PI 3 using aarch64 and allocating a virtual framebuffer larger than the physical frambuffer (for double-buffering purposes), the QEMU window shows the full size of the *virtual* framebuffer rather than the size of the *physical* framebuffer. You can replicate this with code such as: #define FBWIDTH 1024 #define FBHEIGHT 768 void lfb_init() { uart_puts("Initializing Framebuffer\n"); mbox[0] = 35*4; mbox[1] = MBOX_REQUEST; mbox[2] = 0x48003; //set phy wh mbox[3] = 8; mbox[4] = 8; mbox[5] = FBWIDTH; //FrameBufferInfo.width mbox[6] = FBHEIGHT; //FrameBufferInfo.height mbox[7] = 0x48004; //set virt wh mbox[8] = 8; mbox[9] = 8; mbox[10] = FBWIDTH; //FrameBufferInfo.virtual_width mbox[11] = FBHEIGHT * 2; //FrameBufferInfo.virtual_height mbox[12] = 0x48009; //set virt offset mbox[13] = 8; mbox[14] = 8; mbox[15] = 0; //FrameBufferInfo.x_offset mbox[16] = 0; //FrameBufferInfo.y.offset mbox[17] = 0x48005; //set depth mbox[18] = 4; mbox[19] = 4; mbox[20] = 32; //FrameBufferInfo.depth mbox[21] = 0x48006; //set pixel order mbox[22] = 4; mbox[23] = 4; mbox[24] = 1; //RGB, not BGR preferably mbox[25] = 0x40001; //get framebuffer, gets alignment on request mbox[26] = 8; mbox[27] = 8; mbox[28] = 4096; //FrameBufferInfo.pointer mbox[29] = 0; //FrameBufferInfo.size mbox[30] = 0x40008; //get pitch mbox[31] = 4; mbox[32] = 4; mbox[33] = 0; //FrameBufferInfo.pitch mbox[34] = MBOX_TAG_LAST; if(mbox_call(MBOX_CH_PROP) && mbox[20]==32 && mbox[28]!=0) { mbox[28]&=0x3FFFFFFF; fbwidth=mbox[5]; fbheight=mbox[6]; pitch=mbox[33]; lfb=(void*)((unsigned long)mbox[28]); } } I will assume, for the sake of this posting, that the reader understands the mailbox architecture and the appropriate address definitions for them. The key point is that allocating a virtual buffer twice the height of the physical buffer results in QEMU improperly displaying a double-height window. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1777672/+subscriptions
