14.3.3. gem5 graphic mode internals
We cannot use mainline Linux because the gem5 arm Linux kernel patches are required at least to provide the CONFIG_DRM_VIRT_ENCODER option.
gem5 emulates the HDLCD ARM Holdings hardware for arm and aarch64.
The kernel uses HDLCD to implement the DRM interface, the required kernel config options are present at: linux_config/display.
TODO: minimize out the --custom-config-file. If we just remove it on arm: it does not work with a failing dmesg:
[ 0.066208] [drm] found ARM HDLCD version r0p0 [ 0.066241] hdlcd 2b000000.hdlcd: bound virt-encoder (ops drm_vencoder_ops) [ 0.066247] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013). [ 0.066252] [drm] No driver support for vblank timestamp query. [ 0.066276] hdlcd 2b000000.hdlcd: Cannot do DMA to address 0x0000000000000000 [ 0.066281] swiotlb: coherent allocation failed for device 2b000000.hdlcd size=8294400 [ 0.066288] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.15.0 #1 [ 0.066293] Hardware name: V2P-AARCH64 (DT) [ 0.066296] Call trace: [ 0.066301] dump_backtrace+0x0/0x1b0 [ 0.066306] show_stack+0x24/0x30 [ 0.066311] dump_stack+0xb8/0xf0 [ 0.066316] swiotlb_alloc_coherent+0x17c/0x190 [ 0.066321] __dma_alloc+0x68/0x160 [ 0.066325] drm_gem_cma_create+0x98/0x120 [ 0.066330] drm_fbdev_cma_create+0x74/0x2e0 [ 0.066335] __drm_fb_helper_initial_config_and_unlock+0x1d8/0x3a0 [ 0.066341] drm_fb_helper_initial_config+0x4c/0x58 [ 0.066347] drm_fbdev_cma_init_with_funcs+0x98/0x148 [ 0.066352] drm_fbdev_cma_init+0x40/0x50 [ 0.066357] hdlcd_drm_bind+0x220/0x428 [ 0.066362] try_to_bring_up_master+0x21c/0x2b8 [ 0.066367] component_master_add_with_match+0xa8/0xf0 [ 0.066372] hdlcd_probe+0x60/0x78 [ 0.066377] platform_drv_probe+0x60/0xc8 [ 0.066382] driver_probe_device+0x30c/0x478 [ 0.066388] __driver_attach+0x10c/0x128 [ 0.066393] bus_for_each_dev+0x70/0xb0 [ 0.066398] driver_attach+0x30/0x40 [ 0.066402] bus_add_driver+0x1d0/0x298 [ 0.066408] driver_register+0x68/0x100 [ 0.066413] __platform_driver_register+0x54/0x60 [ 0.066418] hdlcd_platform_driver_init+0x20/0x28 [ 0.066424] do_one_initcall+0x44/0x130 [ 0.066428] kernel_init_freeable+0x13c/0x1d8 [ 0.066433] kernel_init+0x18/0x108 [ 0.066438] ret_from_fork+0x10/0x1c [ 0.066444] hdlcd 2b000000.hdlcd: Failed to set initial hw configuration. [ 0.066470] hdlcd 2b000000.hdlcd: master bind failed: -12 [ 0.066477] hdlcd: probe of 2b000000.hdlcd failed with error -12
So what other options are missing from gem5_defconfig? It would be cool to minimize it out to better understand the options.