mmc/bcm2835-sdhost: 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/linux#2728

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
Signed-off-by: ahmedradaideh <ahmed.radaideh@gmail.com>

drivers/mmc/host/bcm2835-sdhost.c

@@ -1244,6 +1244,8 @@ static void bcm2835_sdhost_finish_command(struct bcm2835_host *host,
 				pr_info("%s: ignoring CRC7 error for CMD1\n",
 					mmc_hostname(host->mmc));
 		} else {
+			u32 edm, fsm;
+
 			if (sdhsts & SDHSTS_CMD_TIME_OUT) {
 				if (host->debug)
 					pr_warn("%s: command %d timeout\n",
@@ -1256,6 +1258,13 @@ static void bcm2835_sdhost_finish_command(struct bcm2835_host *host,
 				       host->cmd->opcode);
 				host->cmd->error = -EILSEQ;
 			}
+
+			edm = readl(host->ioaddr + SDEDM);
+			fsm = edm & SDEDM_FSM_MASK;
+			if (fsm == SDEDM_FSM_READWAIT ||
+			    fsm == SDEDM_FSM_WRITESTART1)
+				writel(edm | SDEDM_FORCE_DATA_MODE,
+				       host->ioaddr + SDEDM);
 			tasklet_schedule(&host->finish_tasklet);
 			return;
 		}