From: Arvind Sankar <nivedita@alum.mit.edu>
Date: Mon, 18 May 2020 15:06:55 -0400
Subject: efi/libstub: Buffer output of efi_puts
Patch-mainline: v5.8-rc1
Git-commit: fd0528a24958b7e8d55669cf50749776308d4c5a
References: jsc#SLE-16407

Use a buffer to convert the string to UTF-16. This will reduce the
number of firmware calls required to print the string from one per
character to one per string in most cases.

Cast the input char to unsigned char before converting to efi_char16_t
to avoid sign-extension in case there are any non-ASCII characters in
the input.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200518190716.751506-4-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Lee, Chun-Yi <jlee@suse.com>
---
 drivers/firmware/efi/libstub/efi-stub-helper.c |   19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -8,6 +8,7 @@
  */
 
 #include <linux/efi.h>
+#include <linux/kernel.h>
 #include <asm/efi.h>
 
 #include "efistub.h"
@@ -34,13 +35,19 @@ void efi_char16_puts(efi_char16_t *str)
 
 void efi_puts(const char *str)
 {
-	while (*str) {
-		efi_char16_t ch[] = { *str++, L'\0' };
+	efi_char16_t buf[128];
+	size_t pos = 0, lim = ARRAY_SIZE(buf);
 
-		if (ch[0] == L'\n')
-			efi_char16_puts(L"\r\n");
-		else
-			efi_char16_puts(ch);
+	while (*str) {
+		if (*str == '\n')
+			buf[pos++] = L'\r';
+		/* Cast to unsigned char to avoid sign-extension */
+		buf[pos++] = (unsigned char)(*str++);
+		if (*str == '\0' || pos >= lim - 2) {
+			buf[pos] = L'\0';
+			efi_char16_puts(buf);
+			pos = 0;
+		}
 	}
 }