On Thu, Nov 16, 2023 at 3:36 AM Javier Martinez Canillas <javierm@xxxxxxxxxx> wrote: > > Rob Herring <robh@xxxxxxxxxx> writes: > > Hello Rob, > > > On Mon, Nov 13, 2023 at 2:53 AM Javier Martinez Canillas > > <javierm@xxxxxxxxxx> wrote: > >> > >> Some DT platforms use EFI to boot and in this case the EFI Boot Services > >> may register a EFI_GRAPHICS_OUTPUT_PROTOCOL handle, that will later be > >> queried by the Linux EFI stub to fill the global struct screen_info data. > >> > >> The data is used by the Generic System Framebuffers (sysfb) framework to > >> add a platform device with platform data about the system framebuffer. > >> > >> But if there is a "simple-framebuffer" node in the DT, the OF core will > >> also do the same and add another device for the system framebuffer. > >> > >> This could lead for example, to two platform devices ("simple-framebuffer" > >> and "efi-framebuffer") to be added and matched with their corresponding > >> drivers. So both efifb and simpledrm will be probed, leading to following: > >> > >> [ 0.055752] efifb: framebuffer at 0xbd58dc000, using 16000k, total 16000k > >> [ 0.055755] efifb: mode is 2560x1600x32, linelength=10240, pages=1 > >> [ 0.055758] efifb: scrolling: redraw > >> [ 0.055759] efifb: Truecolor: size=2:10:10:10, shift=30:20:10:0 > >> ... > >> [ 3.295896] simple-framebuffer bd58dc000.framebuffer: [drm] *ERROR* > >> could not acquire memory range [??? 0xffff79f30a29ee40-0x2a5000001a7 > >> flags 0x0]: -16 > >> [ 3.298018] simple-framebuffer: probe of bd58dc000.framebuffer > >> failed with error -16 > >> > >> To prevent the issue, make the OF core to disable sysfb if there is a node > >> with a "simple-framebuffer" compatible. That way only this device will be > >> registered and sysfb would not attempt to register another one using the > >> screen_info data even if this has been filled. > >> > >> This seems the correct thing to do in this case because: > >> > >> a) On a DT platform, the DTB is the single source of truth since is what > >> describes the hardware topology. Even if EFI Boot Services are used to > >> boot the machine. > > > > This is the opposite of what we do for memory and memory reservations. > > EFI is the source of truth for those. > > > > This could also lead to an interesting scenario. As simple-framebuffer > > can define its memory in a /reserved-memory node, but that is ignored > > in EFI boot. Probably would work, but only because EFI probably > > generates its memory map table from the /reserved-memory nodes. > > > > I see. So what would be the solution then? Ignoring creating a platform > device for "simple-framebuffer" if booted using EFI and have an EFI-GOP? Shrug. I don't really know anything more about EFI FB, but I would guess it can't support handling resources like clocks, power domains, regulators, etc. that simple-fb can. So if a platform needs those, do we say they should not setup EFI-GOP? Or is there a use case for having both? Clients that don't muck with resources can use EFI-GOP and those that do use simple-fb. For example, does/can grub use EFI-GOP, but not simple-fb? Rob