[U-Boot] [PATCH 1/1] efi_loader: re-enable GRUB workaround on 32bit ARM

[Heinrich Schuchardt]

GRUB on ARM 32bit prior to version 2.04 lacks proper handling of caches.
In U-Boot v2019.04 a workaround for this was inadvertently removed.

The workaround is currently also needed for booting on systems with caches
that cannot be managed via CP15 (e.g. with an i.MX6 CPU).

Re-enable the workaround and make it customizable.

Fixes: f69d63fae281 ("efi_loader: use efi_start_image() for bootefi")
Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
---
 lib/efi_loader/Kconfig        |  8 ++++++++
 lib/efi_loader/efi_boottime.c | 28 +++++++++++++---------------
 2 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
index a7f2c68fa9..c7027a9676 100644
--- a/lib/efi_loader/Kconfig
+++ b/lib/efi_loader/Kconfig
@@ -107,4 +107,12 @@ config EFI_HAVE_RUNTIME_RESET
 	default y
 	depends on ARCH_BCM283X || FSL_LAYERSCAPE || PSCI_RESET || SYSRESET_X86

+config EFI_GRUB_ARM32_WORKAROUND
+	bool "Workaround for GRUB on 32bit ARM"
+	default y
+	depends on ARM && !ARM64
+	help
+	  GRUB prior to version 2.04 requires U-Boot to disable caches. This
+	  workaround currently is also needed on systems with caches that
+	  cannot be managed via CP15.
 endif
diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
index 4f6e8d1679..f75ca1a67c 100644
--- a/lib/efi_loader/efi_boottime.c
+++ b/lib/efi_loader/efi_boottime.c
@@ -39,14 +39,6 @@ LIST_HEAD(efi_register_notify_events);
 /* Handle of the currently executing image */
 static efi_handle_t current_image;

-/*
- * If we're running on nasty systems (32bit ARM booting into non-EFI Linux)
- * we need to do trickery with caches. Since we don't want to break the EFI
- * aware boot path, only apply hacks when loading exiting directly (breaking
- * direct Linux EFI booting along the way - oh well).
- */
-static bool efi_is_direct_boot = true;
-
 #ifdef CONFIG_ARM
 /*
  * The "gd" pointer lives in a register on ARM and AArch64 that we declare
@@ -1911,13 +1903,21 @@ error:
  */
 static void efi_exit_caches(void)
 {
-#if defined(CONFIG_ARM) && !defined(CONFIG_ARM64)
+#if defined(CONFIG_EFI_GRUB_ARM32_WORKAROUND)
 	/*
-	 * Grub on 32bit ARM needs to have caches disabled before jumping into
-	 * a zImage, but does not know of all cache layers. Give it a hand.
+	 * Boooting Linux via GRUB prior to version 2.04 fails on 32bit ARM if
+	 * caches are enabled.
+	 *
+	 * TODO:
+	 * According to the UEFI spec caches that can be managed via CP15
+	 * operations should be enabled. Caches requiring platform information
+	 * to manage should be disabled. This should not happen in
+	 * ExitBootServices() but before invoking any UEFI binary is invoked.
+	 *
+	 * We want to keep the current workaround while GRUB prior to version
+	 * 2.04 is still in use.
 	 */
-	if (efi_is_direct_boot)
-		cleanup_before_linux();
+	cleanup_before_linux();
 #endif
 }

@@ -2893,8 +2893,6 @@ efi_status_t EFIAPI efi_start_image(efi_handle_t image_handle,
 	if (ret != EFI_SUCCESS)
 		return EFI_EXIT(EFI_INVALID_PARAMETER);

-	efi_is_direct_boot = false;
-
 	image_obj->exit_data_size = exit_data_size;
 	image_obj->exit_data = exit_data;

--
2.20.1