i2c: mxs_i2c: Squash endless loop

The endless waiting for a bit to be set can cause a hang, add a timeout
so we prevent such situation. A testcase for such a hang is below. The
testcase assumes a device to be present at address 0x50 and a device to
NOT be present at address 0x42 . Also note that the "sleep 1" induced
delays are imperative for this bug to manifest .

i2c read 0x42 0x0.2 0x10 0x42000000 ; sleep 1 ; \
i2c read 0x50 0x0.2 0x10 0x42000000 ; sleep 1 ; \
i2c read 0x42 0x0.2 0x10 0x42000000

The expected result of the above command is:

Error reading the chip.
Error reading the chip.

While without this patch, we observe a hang in the last read from 0x42
precisely when waiting for this bit to be set.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Stefano Babic <sbabic@denx.de>

diff --git a/drivers/i2c/mxs_i2c.c b/drivers/i2c/mxs_i2c.c
index 46106b7712e6216c17822faa4cd8f5caa4dc8a52..a298c95e144ae3e35de1b0e2136929b793a282ad 100644 (file)
--- a/drivers/i2c/mxs_i2c.c
+++ b/drivers/i2c/mxs_i2c.c
@@ -150,6 +150,7 @@ int i2c_read(uchar chip, uint addr, int alen, uchar *buffer, int len)
 {
        struct mxs_i2c_regs *i2c_regs = (struct mxs_i2c_regs *)MXS_I2C0_BASE;
        uint32_t tmp = 0;
+       int timeout = MXS_I2C_MAX_TIMEOUT;
        int ret;
        int i;
 
@@ -169,9 +170,17 @@ int i2c_read(uchar chip, uint addr, int alen, uchar *buffer, int len)
 
        for (i = 0; i < len; i++) {
                if (!(i & 3)) {
-                       while (readl(&i2c_regs->hw_i2c_queuestat) &
-                               I2C_QUEUESTAT_RD_QUEUE_EMPTY)
-                               ;
+                       while (--timeout) {
+                               tmp = readl(&i2c_regs->hw_i2c_queuestat);
+                               if (!(tmp & I2C_QUEUESTAT_RD_QUEUE_EMPTY))
+                                       break;
+                       }
+
+                       if (!timeout) {
+                               debug("MXS I2C: Failed receiving data!\n");
+                               return -ETIMEDOUT;
+                       }
+
                        tmp = readl(&i2c_regs->hw_i2c_queuedata);
                }
                buffer[i] = tmp & 0xff;