mmc: mmci: Make busy complete state machine explicit

This refactors the ->busy_complete() callback currently
only used by Ux500 and STM32 to handle busy detection on
hardware where one and the same IRQ is fired whether we get
a start or an end signal on busy detect.

The code is currently using the cached status from the
command IRQ in ->busy_status as a state to select what to
do next: if this state is non-zero we are waiting for
IRQs and if it is zero we treat the state as the starting
point for a busy detect wait cycle.

Make this explicit by creating a state machine where the
->busy_complete callback moves between three states.

The Ux500 busy detect code currently assumes this order:
we enable the busy detect IRQ, get a busy start IRQ, then a
busy end IRQ, and then we clear and mask this IRQ and
proceed.

We insert debug prints for unexpected states.

This works as before on most cards, however on a
problematic card that is not working with busy detect, and
which I have been debugging, the following happens a lot:

[    3.380554] mmci-pl18x 80005000.mmc: no busy signalling in time
[    3.387420] mmci-pl18x 80005000.mmc: no busy signalling in time
[    3.394561] mmci-pl18x 80005000.mmc: lost busy status
     when waiting for busy start IRQ

This probably means that the busy detect start IRQ has
already occurred when we start executing the
->busy_complete() callbacks, and the busy detect end IRQ
is counted as the start IRQ, and this is what is causing
the card to not be detected properly.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230405-pl180-busydetect-fix-v7-5-69a7164f2a61@linaro.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: Linus Walleij

drivers/mmc/host/mmci.c

@@ -680,6 +680,7 @@ static bool ux500_busy_complete(struct mmci_host *host, u32 status, u32 err_msk)
 		writel(host->variant->busy_detect_mask, base + MMCICLEAR);
 		writel(readl(base + MMCIMASK0) &
 		       ~host->variant->busy_detect_mask, base + MMCIMASK0);
+		host->busy_state = MMCI_BUSY_DONE;
 		host->busy_status = 0;
 		return true;
 	}
@@ -697,14 +698,15 @@ static bool ux500_busy_complete(struct mmci_host *host, u32 status, u32 err_msk)
 	 * while, to allow it to be set, but tests indicates that it
 	 * isn't needed.
 	 */
-	if (!host->busy_status) {
+	if (host->busy_state == MMCI_BUSY_DONE) {
 		status = readl(base + MMCISTATUS);
 		if (status & host->variant->busy_detect_flag) {
 			writel(readl(base + MMCIMASK0) |
 			       host->variant->busy_detect_mask,
 			       base + MMCIMASK0);
 
 			host->busy_status = status & (MCI_CMDSENT | MCI_CMDRESPEND);
+			host->busy_state = MMCI_BUSY_WAITING_FOR_START_IRQ;
 			return false;
 		}
 	}
@@ -720,25 +722,34 @@ static bool ux500_busy_complete(struct mmci_host *host, u32 status, u32 err_msk)
 	 * both the start and the end interrupts needs to be cleared,
 	 * one after the other. So, clear the busy start IRQ here.
 	 */
-	if (host->busy_status &&
-	    (status & host->variant->busy_detect_flag)) {
-		host->busy_status |= status & (MCI_CMDSENT | MCI_CMDRESPEND);
-		writel(host->variant->busy_detect_mask, base + MMCICLEAR);
-		return false;
+	if (host->busy_state == MMCI_BUSY_WAITING_FOR_START_IRQ) {
+		if (status & host->variant->busy_detect_flag) {
+			host->busy_status |= status & (MCI_CMDSENT | MCI_CMDRESPEND);
+			writel(host->variant->busy_detect_mask, base + MMCICLEAR);
+			host->busy_state = MMCI_BUSY_WAITING_FOR_END_IRQ;
+			return false;
+		} else {
+			dev_dbg(mmc_dev(host->mmc),
+				"lost busy status when waiting for busy start IRQ\n");
+			writel(host->variant->busy_detect_mask, base + MMCICLEAR);
+			writel(readl(base + MMCIMASK0) &
+			       ~host->variant->busy_detect_mask, base + MMCIMASK0);
+			host->busy_state = MMCI_BUSY_DONE;
+			host->busy_status = 0;
+			return true;
+		}
 	}
 
-	/*
-	 * If there is a command in-progress that has been successfully
-	 * sent and the busy bit isn't set, it means we have received
-	 * the busy end IRQ. Clear and mask the IRQ, then continue to
-	 * process the command.
-	 */
-	if (host->busy_status) {
-		writel(host->variant->busy_detect_mask, base + MMCICLEAR);
-
-		writel(readl(base + MMCIMASK0) &
-		       ~host->variant->busy_detect_mask, base + MMCIMASK0);
-		host->busy_status = 0;
+	if (host->busy_state == MMCI_BUSY_WAITING_FOR_END_IRQ) {
+		if (!(status & host->variant->busy_detect_flag)) {
+			host->busy_status |= status & (MCI_CMDSENT | MCI_CMDRESPEND);
+			host->busy_state = MMCI_BUSY_DONE;
+			return true;
+		} else {
+			dev_dbg(mmc_dev(host->mmc),
+				"busy status still asserted when handling busy end IRQ - will keep waiting\n");
+			return false;
+		}
 	}
 
 	return true;
@@ -1268,6 +1279,8 @@ mmci_start_command(struct mmci_host *host, struct mmc_command *cmd, u32 c)
 	}
 
 	host->busy_status = 0;
+	host->busy_state = MMCI_BUSY_DONE;
+
 	if (host->variant->busy_timeout && cmd->flags & MMC_RSP_BUSY) {
 		if (!cmd->busy_timeout)
 			cmd->busy_timeout = 10 * MSEC_PER_SEC;

drivers/mmc/host/mmci.h

@@ -261,6 +261,19 @@ struct clk;
 struct dma_chan;
 struct mmci_host;
 
+/**
+ * enum mmci_busy_state - enumerate the busy detect wait states
+ *
+ * This is used for the state machine waiting for different busy detect
+ * interrupts on hardware that fire a single IRQ for start and end of
+ * the busy detect phase on DAT0.
+ */
+enum mmci_busy_state {
+	MMCI_BUSY_WAITING_FOR_START_IRQ,
+	MMCI_BUSY_WAITING_FOR_END_IRQ,
+	MMCI_BUSY_DONE,
+};
+
 /**
  * struct variant_data - MMCI variant-specific quirks
  * @clkreg: default value for MCICLOCK register
@@ -409,6 +422,7 @@ struct mmci_host {
 	u32			clk_reg;
 	u32			clk_reg_add;
 	u32			datactrl_reg;
+	enum mmci_busy_state	busy_state;
 	u32			busy_status;
 	u32			mask1_reg;
 	u8			vqmmc_enabled:1;