bootsplash: Add ImageMagick voodoo

The JPEG decoder, that was added many years ago to display a boot-
splash in coreboot, has a few quirks. People used to do some voodoo
with GIMP to convert images to the right format, but we can also
achieve the same with ImageMagick's `convert`. The currently known
constraints are:
* The framebuffer's color format is ignored,
* only YCC 4:2:0 color sampling is supported, and
* width and height have to be a multiple of 16 pixels.

Beside that, we can only display the bootsplash if it completely
fits into the framebuffer. As the latter's size is often decided
at runtime, we can't do much more than offering an option to set
a specific size.

Change-Id: I564e0d89fb46503ff4c11e095726616700009968
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76564
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

1 files changed, 56 insertions, 1 deletions

diff --git a/src/Kconfig b/src/Kconfig
index f5ba4fc784..ea6f341f78 100644
--- a/src/Kconfig
+++ b/src/Kconfig
@@ -447,7 +447,54 @@ config BOOTSPLASH_FILE
 	# Default value set at the end of the file
 	help
 	  The path and filename of the file to use as graphical bootsplash
-	  screen. The file format has to be jpg.
+	  screen. The file format has to be JPEG with YCC 4:2:0 color sampling
+	  unless converted with "Pre-process bootsplash file with ImageMagick".
+
+	  The image can only be displayed by coreboot if it's smaller or has
+	  the same size as the framebuffer resolution. Width and height have
+	  to be a multiple of 16 pixels.
+
+	  Setting these constraints allows a leaner implementation in coreboot.
+	  The minimum necessary ImageMagick command line seems to be:
+	  $ convert input.img -colorspace YCC -sampling-factor 4:2:0 bootsplash.jpg
+
+config BOOTSPLASH_CONVERT
+	bool "Pre-process bootsplash file with ImageMagick"
+	depends on BOOTSPLASH_IMAGE
+	help
+	  Use ImageMagick (`convert` program) to convert a bootsplash image
+	  to the supported JPEG format.
+
+config BOOTSPLASH_CONVERT_QUALITY
+	int "Bootsplash JPEG target quality (%)"
+	depends on BOOTSPLASH_CONVERT
+	range 1 100
+	# Default value set at the end of the file
+
+config BOOTSPLASH_CONVERT_RESIZE
+	bool "Resize bootsplash image"
+	depends on BOOTSPLASH_CONVERT
+	help
+	  Resize the image to the given resolution. Aspect ratio will be kept,
+	  adding black bars as necessary.
+
+config BOOTSPLASH_CONVERT_RESOLUTION
+	string "Bootsplash image target size"
+	depends on BOOTSPLASH_CONVERT_RESIZE
+	# Default value set at the end of the file
+	help
+	  Target image resolution given as <width>x<height>, e.g. 1024x768.
+	  Values not divisible by 16 will be rounded down.
+
+	  When using coreboot to display the bootsplash image (CONFIG_BOOTSPLASH),
+	  set this lower or equal to the minimum resolution you expect.
+
+config BOOTSPLASH_CONVERT_COLORSWAP
+	bool "Swap red and blue color channels"
+	depends on BOOTSPLASH_CONVERT
+	help
+	  The JPEG decoder currently ignores the framebuffer color order.
+	  If your colors seem all wrong, try this option.
 
 config FW_CONFIG
 	bool "Firmware Configuration Probing"
@@ -1444,6 +1491,14 @@ config BOOTSPLASH_FILE
 	depends on BOOTSPLASH_IMAGE
 	default "bootsplash.jpg"
 
+config BOOTSPLASH_CONVERT_QUALITY
+	depends on BOOTSPLASH_CONVERT
+	default 80
+
+config BOOTSPLASH_CONVERT_RESOLUTION
+	depends on BOOTSPLASH_CONVERT_RESIZE
+	default "1024x768"
+
 config CBFS_SIZE
 	default ROM_SIZE