Changeset cbc3587 in mainline

Timestamp:

2018-09-21T21:01:00Z (6 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

631281d

Parents:

8591b31

Message:

Remove infinite loops from kernel ns16550 driver

Replace potential infinite loops by loops with large number of
iterations. This prevents the kernel from hanging when there is no
ns16550 device and the kernel is configured with ns16550 support.

File:

• kernel/genarch/src/drivers/ns16550/ns16550.c (modified) (2 diffs)

kernel/genarch/src/drivers/ns16550/ns16550.c

@@ -47 +47 @@
 #define LSR_TH_READY    0x20
 
+#define RETRY_CNT       100000
+
+#define NOTHING \
+        do { \
+        } while(0)
+
+#define WHILE_CNT_AND_COND_DO(cnt, expr, statement) \
+        do { \
+                for (volatile unsigned i = 0; i < (cnt); i++) \
+                        if ((expr)) \
+                                statement; \
+                        else \
+                                break; \
+        } while (0)
+
 static uint8_t ns16550_reg_read(ns16550_instance_t *inst, ns16550_reg_t reg)
 {
@@ -78 +93 @@
 }
 
-/**< Clear input buffer. */
+/** Clear input buffer. */
 static void ns16550_clear_buffer(ns16550_instance_t *instance)
 {
-        while (ns16550_reg_read(instance, NS16550_REG_LSR) & LSR_DATA_READY)
-                (void) ns16550_reg_read(instance, NS16550_REG_RBR);
+        WHILE_CNT_AND_COND_DO(RETRY_CNT,
+            ns16550_reg_read(instance, NS16550_REG_LSR) & LSR_DATA_READY,
+            (void) ns16550_reg_read(instance, NS16550_REG_RBR));
 }
 
 static void ns16550_sendb(ns16550_instance_t *instance, uint8_t byte)
 {
-        while (!(ns16550_reg_read(instance, NS16550_REG_LSR) & LSR_TH_READY))
-                ;
+        WHILE_CNT_AND_COND_DO(RETRY_CNT,
+            !(ns16550_reg_read(instance, NS16550_REG_LSR) & LSR_TH_READY),
+            NOTHING);
+
         ns16550_reg_write(instance, NS16550_REG_THR, byte);
 }