On 18 June 2018 at 10:30, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > Hi, > > On 18-06-18 09:36, Ard Biesheuvel wrote: >> >> Hallo Hans, >> >> On 17 June 2018 at 17:32, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: >>> >>> On systems where fbcon is configured for deferred console takeover, the >>> intend is for the framebuffer to show the boot graphics (e.g a vendor >>> logo) until some message (e.g. an error) is printed or a graphical >>> session takes over. >>> >>> Some firmware however relies on the OS to show the boot graphics >>> (indicated by bgrt_tab.status being 0) and the boot graphics may have >>> been destroyed by e.g. the grub boot menu. >>> >>> This patch adds support to efifb to show the boot graphics and >>> automatically enables this when fbcon is configured for deferred >>> console takeover. >>> >>> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx> >> >> >> I have tested this code on ARM QEMU/mach-virt, and with a little tweak >> (which I will post separately), the code works as expected, i.e., it >> redraws the boot logo based on the contents of the BGRT table. > > > That is great. > >> However, what it doesn't do is clear the screen, which means the logo >> is drawn on top of whatever the boot environment left behind, and I >> end up with something like this. >> >> http://people.linaro.org/~ard.biesheuvel/mach-virt-bgrt-logo-redrawn.png > > > Hmm, less great. I'm not sure how to deal with this, on x86 it is more > or less guaranteed that the screen is already cleared when we load and > clearing a 4k screen means writing about 32MB, which I guess with modern > RAM speeds is not that bad actually. > > I see that you got this picture by manual booting from the EFI shell, > in what state does the firmware / bootloader normally leave the > framebuffer? UEFI does not usually clear the screen when it boots the default entry, so it is entirely dependent on the boot loader that runs next. I guess GRUB usually clears the screen unconditionally? In any case, I think it is reasonable to clear the screen if you redraw the logo, but I do wonder if it is safe to assume that the background color is black. Instead, we may decide to clear the screen before ExitBootServices() [using EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL.ClearScreen()]. > I'm asking because if normally it is either cleared > to black, or already showing the logo I wonder if we should take the > (small) penalty of clearing ? > > Given that we are talking about only 32 MB I could do a v2 which just > memsets the rest of the screen to 0. > > So we get: > > for (y= 0; y < height; y++) { > if (line_part_of_bgrt) { > memset(left-of-bgrt); > draw_bgrt_line(y); > memset(right-of-bgrt); > } else { > memset(line); > } > } > > Note I've deliberately done the if on a per line > base to keep the actual blit part of the loop > efficient and without any extra conditionals in > there. I also don't simply first memset the entire > fb to 0 to avoid a flash / tearing if the bgrt > image is already in place (which happens often on > x86). > > Implementing this is easy and as said the extra execution time should > be quite small, still I wonder what others think about this? > > I'm leaning towards doing the clearing / memsets since I've seen > some firmwares leave some artifacts from not completely clearing > things like a "Press F2 to enter setup" message, missing a few > pixels and leaving those on screen. > I think the overhead of doing the clearing is not going to be the bottleneck. But redrawing a logo on black background that was designed to be displayed over another color is going to look really ugly ... -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
