mmc/bcm2835: Recover from MMC_SEND_EXT_CSD

If the user issues an "mmc extcsd read", the SD controller receives
what it thinks is a SEND_IF_COND command with an unexpected data block.
The resulting operations leave the FSM stuck in READWAIT, a state which
persists until the MMC framework resets the controller, by which point
the root filesystem is likely to have been unmounted.

A less heavyweight solution is to detect the condition and nudge the
FSM by asserting the (self-clearing) FORCE_DATA_MODE bit.

N.B. This workaround was essentially discovered by accident and without
a full understanding the inner workings of the controller, so it is
fortunate that the "fix" only modifies error paths.

See: raspberrypi#2728

Signed-off-by: Phil Elwell <phil@raspberrypi.org>

drivers/mmc/host/bcm2835.c

@@ -772,6 +772,8 @@ static void bcm2835_finish_command(struct bcm2835_host *host)
 
 		if (!(sdhsts & SDHSTS_CRC7_ERROR) ||
 		    (host->cmd->opcode != MMC_SEND_OP_COND)) {
+			u32 edm, fsm;
+
 			if (sdhsts & SDHSTS_CMD_TIME_OUT) {
 				host->cmd->error = -ETIMEDOUT;
 			} else {
@@ -780,6 +782,13 @@ static void bcm2835_finish_command(struct bcm2835_host *host)
 				bcm2835_dumpregs(host);
 				host->cmd->error = -EILSEQ;
 			}
+			edm = readl(host->ioaddr + SDEDM);
+			fsm = edm & SDEDM_FSM_MASK;
+			if (fsm == SDEDM_FSM_READWAIT ||
+			    fsm == SDEDM_FSM_WRITESTART1)
+				/* Kick the FSM out of its wait */
+				writel(edm | SDEDM_FORCE_DATA_MODE,
+				       host->ioaddr + SDEDM);
 			bcm2835_finish_request(host);
 			return;
 		}