GRUB EFI Serial Read workaround for 3A5000

grub-serial.patch

diff --git a/grub-core/term/efi/serial.c b/grub-core/term/efi/serial.c
index 4c94723..0caa724 100644
--- a/grub-core/term/efi/serial.c
+++ b/grub-core/term/efi/serial.c
@@ -65,20 +65,52 @@ do_real_config (struct grub_serial_port *port)
   port->configured = 1;
 }
 
+#define SERIAL_BASE 0x800000001fe001e0ul
+
+#define SERIAL_DAT 0
+#define SERIAL_DLL 0
+#define SERIAL_DLM 1
+#define SERIAL_IER 1
+#define SERIAL_IIR 2
+#define SERIAL_FCR 2
+#define SERIAL_LCR 3
+#define SERIAL_MCR 4
+#define SERIAL_LSR 5
+
+#define SERIAL_LCR_DLAB 0x80
+#define SERIAL_LSR_TE   0x20
+
+#define PORT(base, offset) (volatile unsigned char *)(base + offset)
+
+static inline unsigned int
+serial_in (int offset)
+{
+    return *(PORT(SERIAL_BASE, offset));
+}
+
+static int
+serial_read (void *buf, int len)
+{
+    unsigned char *data = buf;
+    int i;
+
+    for (i=0; i<len; i++) {
+        while ((serial_in (SERIAL_LSR) & 1) == 0) {
+            grub_efi_stall(10);
+        }
+        data[i] = serial_in (SERIAL_DAT);
+    }
+
+    return len;
+}
+
 /* Fetch a key.  */
 static int
 serial_hw_fetch (struct grub_serial_port *port)
 {
-  grub_efi_uintn_t bufsize = 1;
   char c;
-  grub_efi_status_t status = GRUB_EFI_SUCCESS;
-  do_real_config (port);
-  if (port->broken)
-    return -1;
 
-  status = efi_call_3 (port->interface->read, port->interface, &bufsize, &c);
-  if (status != GRUB_EFI_SUCCESS || bufsize == 0)
-    return -1;
+  serial_read (&c, sizeof (c));
 
   return c;
 }