mmc: sunxi: Lock fix

1) Adding a comment in order to clarify the choice of the locks within
sunxi_mmc_handle_manual_stop

2) As <lixiang@allwinnertech.com> has pointed out the wait_dma variable
was not accessed within the spin lock block in sunxi_mmc_request and so
(even if it should never happend) it would have theoretically been
possible that some other function would access the variable at the same
time as the function. This has been changed now and the function is
using local variables outside the lock and copys the value over during
the lock phase.

Signed-off-by: David Lanzendörfer <david.lanzendoerfer@o2s.ch>
Reported-by: <lixiang@allwinnertech.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sunxi-mmc.c

@@ -572,6 +572,15 @@ static irqreturn_t sunxi_mmc_handle_manual_stop(int irq, void *dev_id)
 	}
 
 	dev_err(mmc_dev(host->mmc), "data error, sending stop command\n");
+
+	/*
+	 * We will never have more than one outstanding request,
+	 * and we do not complete the request until after
+	 * we've cleared host->manual_stop_mrq so we do not need to
+	 * spin lock this function.
+	 * Additionally we have wait states within this function
+	 * so having it in a lock is a very bad idea.
+	 */
 	sunxi_mmc_send_manual_stop(host, mrq);
 
 	spin_lock_irqsave(&host->lock, iflags);
@@ -768,6 +777,7 @@ static void sunxi_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
 	unsigned long iflags;
 	u32 imask = SDXC_INTERRUPT_ERROR_BIT;
 	u32 cmd_val = SDXC_START | (cmd->opcode & 0x3f);
+	bool wait_dma = host->wait_dma;
 	int ret;
 
 	/* Check for set_ios errors (should never happen) */
@@ -818,7 +828,7 @@ static void sunxi_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
 			if (cmd->data->flags & MMC_DATA_WRITE)
 				cmd_val |= SDXC_WRITE;
 			else
-				host->wait_dma = true;
+				wait_dma = true;
 		} else {
 			imask |= SDXC_COMMAND_DONE;
 		}
@@ -852,6 +862,7 @@ static void sunxi_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
 	}
 
 	host->mrq = mrq;
+	host->wait_dma = wait_dma;
 	mmc_writel(host, REG_IMASK, host->sdio_imask | imask);
 	mmc_writel(host, REG_CARG, cmd->arg);
 	mmc_writel(host, REG_CMDR, cmd_val);