If an EFI application frequently repeats SetTime and GetTime,
the I2C bus can be busy and failed to start. To fix this issue,
add waiting loop for the bus busy status. (Usually, it is
enough to read 3 times for checking, but for safety this
sets 10 for timeout.)

This also clean up the code path a bit so that it is easy to
understand what should do on each combinations of BSR.BB and
BCR.MSS.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
Reported-by: Kazuhiko Sakamoto <sakamoto.kazuhiko@socionext.com>
Contributed-under: TianoCore Contribution Agreement 1.1
---
 .../Drivers/SynQuacerI2cDxe/SynQuacerI2cDxe.c      |   38 ++++++++++++++------
 1 file changed, 26 insertions(+), 12 deletions(-)

diff --git a/Silicon/Socionext/SynQuacer/Drivers/SynQuacerI2cDxe/SynQuacerI2cDxe.c b/Silicon/Socionext/SynQuacer/Drivers/SynQuacerI2cDxe/SynQuacerI2cDxe.c
index 31f6e3072f..380eba8059 100644
--- a/Silicon/Socionext/SynQuacer/Drivers/SynQuacerI2cDxe/SynQuacerI2cDxe.c
+++ b/Silicon/Socionext/SynQuacer/Drivers/SynQuacerI2cDxe/SynQuacerI2cDxe.c
@@ -16,6 +16,8 @@
 //
 #define WAIT_FOR_INTERRUPT_TIMEOUT    50000
 
+#define WAIT_FOR_BUS_BUSY_TIMEOUT        10
+
 /**
   Set the frequency for the I2C clock line.
 
@@ -152,6 +154,7 @@ SynQuacerI2cMasterStart (
   IN  EFI_I2C_OPERATION           *Op
   )
 {
+  UINTN                   Timeout = WAIT_FOR_BUS_BUSY_TIMEOUT;
   UINT8                       Bsr;
   UINT8                       Bcr;
 
@@ -167,24 +170,35 @@ SynQuacerI2cMasterStart (
   Bsr = MmioRead8 (I2c->MmioBase + F_I2C_REG_BSR);
   Bcr = MmioRead8 (I2c->MmioBase + F_I2C_REG_BCR);
 
-  if ((Bsr & F_I2C_BSR_BB) && !(Bcr & F_I2C_BCR_MSS)) {
-    DEBUG ((DEBUG_INFO, "%a: bus is busy\n", __FUNCTION__));
-    return EFI_ALREADY_STARTED;
-  }
+  if (!(Bcr & F_I2C_BCR_MSS)) {
 
-  if (Bsr & F_I2C_BSR_BB) { // Bus is busy
-    DEBUG ((DEBUG_INFO, "%a: Continuous Start\n", __FUNCTION__));
-    MmioWrite8 (I2c->MmioBase + F_I2C_REG_BCR, Bcr | F_I2C_BCR_SCC);
-  } else {
-    if (Bcr & F_I2C_BCR_MSS) {
-      DEBUG ((DEBUG_WARN,
-        "%a: is not in master mode\n", __FUNCTION__));
-      return EFI_DEVICE_ERROR;
+    if (Bsr & F_I2C_BSR_BB) { // Bus is busy
+        do {
+          Bsr = MmioRead8 (I2c->MmioBase + F_I2C_REG_BSR);
+        } while (Timeout-- && (Bsr & F_I2C_BSR_BB));
+
+        if (Bsr & F_I2C_BSR_BB) {
+          DEBUG ((DEBUG_INFO, "%a: bus is busy\n", __FUNCTION__));
+          return EFI_ALREADY_STARTED;
+        }
     }
+
     DEBUG ((DEBUG_INFO, "%a: Start Condition\n", __FUNCTION__));
     MmioWrite8 (I2c->MmioBase + F_I2C_REG_BCR,
                 Bcr | F_I2C_BCR_MSS | F_I2C_BCR_INTE | F_I2C_BCR_BEIE);
+
+  } else { // F_I2C_BCR_MSS is set
+
+    if (!(Bsr & F_I2C_BSR_BB)) {
+      DEBUG ((DEBUG_WARN,
+        "%a: is not in master mode\n", __FUNCTION__));
+      return EFI_DEVICE_ERROR;
+    }
+
+    DEBUG ((DEBUG_INFO, "%a: Continuous Start\n", __FUNCTION__));
+    MmioWrite8 (I2c->MmioBase + F_I2C_REG_BCR, Bcr | F_I2C_BCR_SCC);
   }
+
   return EFI_SUCCESS;
 }
 



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