Commit eb5381fd authored by Phil Elwell's avatar Phil Elwell Committed by Phil Elwell
Browse files

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: https://github.com/raspberrypi/linux/issues/2728



Signed-off-by: default avatarPhil Elwell <phil@raspberrypi.org>
parent 961aa235

drivers/mmc/host/bcm2835-sdhost.c

+9 −0
Original line number Diff line number Diff line
@@ -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;

		}