[PATCH v2 2/4] mmc: dw_mmc: avoid race condition of cpu and IDMAC

[Shawn Lin]

We could see an obvious race condition by test that
the former write operation by IDMAC aiming to clear
OWN bit reach right after the later configuration of
the same desc, which makes the IDMAC be in SUSPEND
state as the OWN bit was cleared by the asynchronous
write operation of IDMAC. The bug can be very easy
reproduced on RK3288 or similar when we reduce the
running rate of system buses and keep the CPU running
faster. So as two separate masters, IDMAC and cpu
write the same descriptor stored on the same address,
and this should be protected by adding check of OWN
bit before preparing new descriptors.

Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>

---

Changes in v2:
- fallback to PIO mode if failing to wait for OWN bit
- cleanup polluted desc chain as the own bit error could
  occur on any place of the chain, so we need to clr the desc
  configured before that one. Use the exist function to reinit
  the desc chain. As this issue is really rare, so after applied,
  the fio/iozone stress test didn't show up performance regression.

 drivers/mmc/host/dw_mmc.c | 208 ++++++++++++++++++++++++++++------------------
 1 file changed, 129 insertions(+), 79 deletions(-)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index 782b303..daa1c52 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -467,12 +467,87 @@ static void dw_mci_dmac_complete_dma(void *arg)
 	}
 }
 
-static inline void dw_mci_prepare_desc64(struct dw_mci *host,
+static int dw_mci_idmac_init(struct dw_mci *host)
+{
+	int i;
+
+	if (host->dma_64bit_address == 1) {
+		struct idmac_desc_64addr *p;
+		/* Number of descriptors in the ring buffer */
+		host->ring_size = PAGE_SIZE / sizeof(struct idmac_desc_64addr);
+
+		/* Forward link the descriptor list */
+		for (i = 0, p = host->sg_cpu; i < host->ring_size - 1;
+								i++, p++) {
+			p->des6 = (host->sg_dma +
+					(sizeof(struct idmac_desc_64addr) *
+							(i + 1))) & 0xffffffff;
+
+			p->des7 = (u64)(host->sg_dma +
+					(sizeof(struct idmac_desc_64addr) *
+							(i + 1))) >> 32;
+			/* Initialize reserved and buffer size fields to "0" */
+			p->des1 = 0;
+			p->des2 = 0;
+			p->des3 = 0;
+		}
+
+		/* Set the last descriptor as the end-of-ring descriptor */
+		p->des6 = host->sg_dma & 0xffffffff;
+		p->des7 = (u64)host->sg_dma >> 32;
+		p->des0 = IDMAC_DES0_ER;
+
+	} else {
+		struct idmac_desc *p;
+		/* Number of descriptors in the ring buffer */
+		host->ring_size = PAGE_SIZE / sizeof(struct idmac_desc);
+
+		/* Forward link the descriptor list */
+		for (i = 0, p = host->sg_cpu;
+		     i < host->ring_size - 1;
+		     i++, p++) {
+			p->des3 = cpu_to_le32(host->sg_dma +
+					(sizeof(struct idmac_desc) * (i + 1)));
+			p->des1 = 0;
+		}
+
+		/* Set the last descriptor as the end-of-ring descriptor */
+		p->des3 = cpu_to_le32(host->sg_dma);
+		p->des0 = cpu_to_le32(IDMAC_DES0_ER);
+	}
+
+	dw_mci_idmac_reset(host);
+
+	if (host->dma_64bit_address == 1) {
+		/* Mask out interrupts - get Tx & Rx complete only */
+		mci_writel(host, IDSTS64, IDMAC_INT_CLR);
+		mci_writel(host, IDINTEN64, SDMMC_IDMAC_INT_NI |
+				SDMMC_IDMAC_INT_RI | SDMMC_IDMAC_INT_TI);
+
+		/* Set the descriptor base address */
+		mci_writel(host, DBADDRL, host->sg_dma & 0xffffffff);
+		mci_writel(host, DBADDRU, (u64)host->sg_dma >> 32);
+
+	} else {
+		/* Mask out interrupts - get Tx & Rx complete only */
+		mci_writel(host, IDSTS, IDMAC_INT_CLR);
+		mci_writel(host, IDINTEN, SDMMC_IDMAC_INT_NI |
+				SDMMC_IDMAC_INT_RI | SDMMC_IDMAC_INT_TI);
+
+		/* Set the descriptor base address */
+		mci_writel(host, DBADDR, host->sg_dma);
+	}
+
+	return 0;
+}
+
+static inline int dw_mci_prepare_desc64(struct dw_mci *host,
 					 struct mmc_data *data,
 					 unsigned int sg_len)
 {
 	unsigned int desc_len;
 	struct idmac_desc_64addr *desc_first, *desc_last, *desc;
+	unsigned long timeout;
 	int i;
 
 	desc_first = desc_last = desc = host->sg_cpu;
@@ -489,6 +564,19 @@ static inline void dw_mci_prepare_desc64(struct dw_mci *host,
 			length -= desc_len;
 
 			/*
+			 * Wait for the former clear OWN bit operation
+			 * of IDMAC to make sure that this descriptor
+			 * isn't still owned by IDMAC as IDMAC's write
+			 * ops and CPU's read ops are asynchronous.
+			 */
+			timeout = jiffies + msecs_to_jiffies(100);
+			while (readl(&desc->des0) & IDMAC_DES0_OWN) {
+				if (time_after(jiffies, timeout))
+					goto err_own_bit;
+				udelay(10);
+			}
+
+			/*
 			 * Set the OWN bit and disable interrupts
 			 * for this descriptor
 			 */
@@ -516,15 +604,24 @@ static inline void dw_mci_prepare_desc64(struct dw_mci *host,
 	/* Set last descriptor */
 	desc_last->des0 &= ~(IDMAC_DES0_CH | IDMAC_DES0_DIC);
 	desc_last->des0 |= IDMAC_DES0_LD;
+
+	return 0;
+err_own_bit:
+	/* restore the descriptor chain as it's polluted */
+	dev_dbg(host->dev, "desciptor is still owned by IDMAC.\n");
+	memset(host->sg_cpu, 0, PAGE_SIZE);
+	dw_mci_idmac_init(host);
+	return -EINVAL;
 }
 
 
-static inline void dw_mci_prepare_desc32(struct dw_mci *host,
+static inline int dw_mci_prepare_desc32(struct dw_mci *host,
 					 struct mmc_data *data,
 					 unsigned int sg_len)
 {
 	unsigned int desc_len;
 	struct idmac_desc *desc_first, *desc_last, *desc;
+	unsigned long timeout;
 	int i;
 
 	desc_first = desc_last = desc = host->sg_cpu;
@@ -541,6 +638,20 @@ static inline void dw_mci_prepare_desc32(struct dw_mci *host,
 			length -= desc_len;
 
 			/*
+			 * Wait for the former clear OWN bit operation
+			 * of IDMAC to make sure that this descriptor
+			 * isn't still owned by IDMAC as IDMAC's write
+			 * ops and CPU's read ops are asynchronous.
+			 */
+			timeout = jiffies + msecs_to_jiffies(100);
+			while (readl(&desc->des0) &
+			       cpu_to_le32(IDMAC_DES0_OWN)) {
+				if (time_after(jiffies, timeout))
+					goto err_own_bit;
+				udelay(10);
+			}
+
+			/*
 			 * Set the OWN bit and disable interrupts
 			 * for this descriptor
 			 */
@@ -569,16 +680,28 @@ static inline void dw_mci_prepare_desc32(struct dw_mci *host,
 	desc_last->des0 &= cpu_to_le32(~(IDMAC_DES0_CH |
 				       IDMAC_DES0_DIC));
 	desc_last->des0 |= cpu_to_le32(IDMAC_DES0_LD);
+
+	return 0;
+err_own_bit:
+	/* restore the descriptor chain as it's polluted */
+	dev_dbg(host->dev, "desciptor is still owned by IDMAC.\n");
+	memset(host->sg_cpu, 0, PAGE_SIZE);
+	dw_mci_idmac_init(host);
+	return -EINVAL;
 }
 
 static int dw_mci_idmac_start_dma(struct dw_mci *host, unsigned int sg_len)
 {
 	u32 temp;
+	int ret;
 
 	if (host->dma_64bit_address == 1)
-		dw_mci_prepare_desc64(host, host->data, sg_len);
+		ret = dw_mci_prepare_desc64(host, host->data, sg_len);
 	else
-		dw_mci_prepare_desc32(host, host->data, sg_len);
+		ret = dw_mci_prepare_desc32(host, host->data, sg_len);
+
+	if (ret)
+		goto out;
 
 	/* drain writebuffer */
 	wmb();
@@ -603,81 +726,8 @@ static int dw_mci_idmac_start_dma(struct dw_mci *host, unsigned int sg_len)
 	/* Start it running */
 	mci_writel(host, PLDMND, 1);
 
-	return 0;
-}
-
-static int dw_mci_idmac_init(struct dw_mci *host)
-{
-	int i;
-
-	if (host->dma_64bit_address == 1) {
-		struct idmac_desc_64addr *p;
-		/* Number of descriptors in the ring buffer */
-		host->ring_size = PAGE_SIZE / sizeof(struct idmac_desc_64addr);
-
-		/* Forward link the descriptor list */
-		for (i = 0, p = host->sg_cpu; i < host->ring_size - 1;
-								i++, p++) {
-			p->des6 = (host->sg_dma +
-					(sizeof(struct idmac_desc_64addr) *
-							(i + 1))) & 0xffffffff;
-
-			p->des7 = (u64)(host->sg_dma +
-					(sizeof(struct idmac_desc_64addr) *
-							(i + 1))) >> 32;
-			/* Initialize reserved and buffer size fields to "0" */
-			p->des1 = 0;
-			p->des2 = 0;
-			p->des3 = 0;
-		}
-
-		/* Set the last descriptor as the end-of-ring descriptor */
-		p->des6 = host->sg_dma & 0xffffffff;
-		p->des7 = (u64)host->sg_dma >> 32;
-		p->des0 = IDMAC_DES0_ER;
-
-	} else {
-		struct idmac_desc *p;
-		/* Number of descriptors in the ring buffer */
-		host->ring_size = PAGE_SIZE / sizeof(struct idmac_desc);
-
-		/* Forward link the descriptor list */
-		for (i = 0, p = host->sg_cpu;
-		     i < host->ring_size - 1;
-		     i++, p++) {
-			p->des3 = cpu_to_le32(host->sg_dma +
-					(sizeof(struct idmac_desc) * (i + 1)));
-			p->des1 = 0;
-		}
-
-		/* Set the last descriptor as the end-of-ring descriptor */
-		p->des3 = cpu_to_le32(host->sg_dma);
-		p->des0 = cpu_to_le32(IDMAC_DES0_ER);
-	}
-
-	dw_mci_idmac_reset(host);
-
-	if (host->dma_64bit_address == 1) {
-		/* Mask out interrupts - get Tx & Rx complete only */
-		mci_writel(host, IDSTS64, IDMAC_INT_CLR);
-		mci_writel(host, IDINTEN64, SDMMC_IDMAC_INT_NI |
-				SDMMC_IDMAC_INT_RI | SDMMC_IDMAC_INT_TI);
-
-		/* Set the descriptor base address */
-		mci_writel(host, DBADDRL, host->sg_dma & 0xffffffff);
-		mci_writel(host, DBADDRU, (u64)host->sg_dma >> 32);
-
-	} else {
-		/* Mask out interrupts - get Tx & Rx complete only */
-		mci_writel(host, IDSTS, IDMAC_INT_CLR);
-		mci_writel(host, IDINTEN, SDMMC_IDMAC_INT_NI |
-				SDMMC_IDMAC_INT_RI | SDMMC_IDMAC_INT_TI);
-
-		/* Set the descriptor base address */
-		mci_writel(host, DBADDR, host->sg_dma);
-	}
-
-	return 0;
+out:
+	return ret;
 }
 
 static const struct dw_mci_dma_ops dw_mci_idmac_ops = {
-- 
2.3.7