efi_loader: clear screen should move cursor to home

On a VT100 terminal <ESC>[2J should be enough to both clear the whole
screen and set the cursor to position (1, 1). But the Linux console does
not behave like this. So send an extra <ESC>[H. For reference see the
console_codes(4) man page.

Add a function description.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

diff --git a/lib/efi_loader/efi_console.c b/lib/efi_loader/efi_console.c
index 218f7ca..8494044 100644 (file)
--- a/lib/efi_loader/efi_console.c
+++ b/lib/efi_loader/efi_console.c
@@ -360,12 +360,26 @@ static efi_status_t EFIAPI efi_cout_set_attribute(
        return EFI_EXIT(EFI_SUCCESS);
 }
 
+/**
+ * efi_cout_clear_screen() - clear screen
+ *
+ * This function implements the ClearScreen service of the
+ * EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL. See the Unified Extensible Firmware
+ * Interface (UEFI) specification for details.
+ *
+ * @this:      pointer to the protocol instance
+ * Return:     status code
+ */
 static efi_status_t EFIAPI efi_cout_clear_screen(
                        struct efi_simple_text_output_protocol *this)
 {
        EFI_ENTRY("%p", this);
 
-       printf(ESC"[2J");
+       /*
+        * The Linux console wants both a clear and a home command. The video
+        * uclass does not support <ESC>[H without coordinates, yet.
+        */
+       printf(ESC "[2J" ESC "[1;1H");
        efi_con_mode.cursor_column = 0;
        efi_con_mode.cursor_row = 0;