[PATCH v2] tpm_tis_spi: Use DMA-safe memory for SPI transfers

[PATCH v2] tpm_tis_spi: Use DMA-safe memory for SPI transfers

[Alexander Steffen]

The buffers used as tx_buf/rx_buf in a SPI transfer need to be DMA-safe.
This cannot be guaranteed for the buffers passed to tpm_tis_spi_read_bytes
and tpm_tis_spi_write_bytes. Therefore, we need to use our own DMA-safe
buffer and copy the data to/from it.

A single buffer is sufficient for both tx and rx, since bytes that have
already been sent are not used anymore and can safely be overwritten with
the received bytes. The buffer needs to be allocated separately, to ensure
that it is cacheline-aligned and not shared with other data, so that DMA
can work correctly.

Fixes: 0edbfea537d1 ("tpm/tpm_tis_spi: Add support for spi phy")
Cc: stable@vger.kernel.org
Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
---
v2: Updated commit message with more explanations.

 drivers/char/tpm/tpm_tis_spi.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
index 88fe72a..5321245 100644
--- a/drivers/char/tpm/tpm_tis_spi.c
+++ b/drivers/char/tpm/tpm_tis_spi.c
@@ -46,9 +46,7 @@
 struct tpm_tis_spi_phy {
 	struct tpm_tis_data priv;
 	struct spi_device *spi_device;
-
-	u8 tx_buf[4];
-	u8 rx_buf[4];
+	u8 *iobuf;
 };
 
 static inline struct tpm_tis_spi_phy *to_tpm_tis_spi_phy(struct tpm_tis_data *data)
@@ -71,14 +69,14 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
 	while (len) {
 		transfer_len = min_t(u16, len, MAX_SPI_FRAMESIZE);
 
-		phy->tx_buf[0] = direction | (transfer_len - 1);
-		phy->tx_buf[1] = 0xd4;
-		phy->tx_buf[2] = addr >> 8;
-		phy->tx_buf[3] = addr;
+		phy->iobuf[0] = direction | (transfer_len - 1);
+		phy->iobuf[1] = 0xd4;
+		phy->iobuf[2] = addr >> 8;
+		phy->iobuf[3] = addr;
 
 		memset(&spi_xfer, 0, sizeof(spi_xfer));
-		spi_xfer.tx_buf = phy->tx_buf;
-		spi_xfer.rx_buf = phy->rx_buf;
+		spi_xfer.tx_buf = phy->iobuf;
+		spi_xfer.rx_buf = phy->iobuf;
 		spi_xfer.len = 4;
 		spi_xfer.cs_change = 1;
 
@@ -88,9 +86,9 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
 		if (ret < 0)
 			goto exit;
 
-		if ((phy->rx_buf[3] & 0x01) == 0) {
+		if ((phy->iobuf[3] & 0x01) == 0) {
 			// handle SPI wait states
-			phy->tx_buf[0] = 0;
+			phy->iobuf[0] = 0;
 
 			for (i = 0; i < TPM_RETRY; i++) {
 				spi_xfer.len = 1;
@@ -99,7 +97,7 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
 				ret = spi_sync_locked(phy->spi_device, &m);
 				if (ret < 0)
 					goto exit;
-				if (phy->rx_buf[0] & 0x01)
+				if (phy->iobuf[0] & 0x01)
 					break;
 			}
 
@@ -115,10 +113,9 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
 
 		if (direction) {
 			spi_xfer.tx_buf = NULL;
-			spi_xfer.rx_buf = buffer;
 		} else {
-			spi_xfer.tx_buf = buffer;
 			spi_xfer.rx_buf = NULL;
+			memcpy(phy->iobuf, buffer, transfer_len);
 		}
 
 		spi_message_init(&m);
@@ -127,6 +124,9 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
 		if (ret < 0)
 			goto exit;
 
+		if (direction)
+			memcpy(buffer, phy->iobuf, transfer_len);
+
 		len -= transfer_len;
 		buffer += transfer_len;
 	}
@@ -194,6 +194,10 @@ static int tpm_tis_spi_probe(struct spi_device *dev)
 
 	phy->spi_device = dev;
 
+	phy->iobuf = devm_kmalloc(&dev->dev, MAX_SPI_FRAMESIZE, GFP_KERNEL);
+	if (!phy->iobuf)
+		return -ENOMEM;
+
 	return tpm_tis_core_init(&dev->dev, &phy->priv, -1, &tpm_spi_phy_ops,
 				 NULL);
 }
-- 
2.7.4

Re: [PATCH v2] tpm_tis_spi: Use DMA-safe memory for SPI transfers

[Jarkko Sakkinen]

On Fri, Aug 18, 2017 at 02:14:57PM +0200, Alexander Steffen wrote:
> The buffers used as tx_buf/rx_buf in a SPI transfer need to be DMA-safe.
> This cannot be guaranteed for the buffers passed to tpm_tis_spi_read_bytes
> and tpm_tis_spi_write_bytes. Therefore, we need to use our own DMA-safe
> buffer and copy the data to/from it.
> 
> A single buffer is sufficient for both tx and rx, since bytes that have
> already been sent are not used anymore and can safely be overwritten with
> the received bytes. The buffer needs to be allocated separately, to ensure
> that it is cacheline-aligned and not shared with other data, so that DMA
> can work correctly.
> 
> Fixes: 0edbfea537d1 ("tpm/tpm_tis_spi: Add support for spi phy")
> Cc: stable@vger.kernel.org
> Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>

90% of this patch is about merging the buffers and 10% is the bug fix
that you even want to stable, right?

So please create a patch that does the fix without merging the buffers.
In this form this is pain to backport to stable.

/Jarkko

> ---
> v2: Updated commit message with more explanations.
> 
>  drivers/char/tpm/tpm_tis_spi.c | 32 ++++++++++++++++++--------------
>  1 file changed, 18 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
> index 88fe72a..5321245 100644
> --- a/drivers/char/tpm/tpm_tis_spi.c
> +++ b/drivers/char/tpm/tpm_tis_spi.c
> @@ -46,9 +46,7 @@
>  struct tpm_tis_spi_phy {
>  	struct tpm_tis_data priv;
>  	struct spi_device *spi_device;
> -
> -	u8 tx_buf[4];
> -	u8 rx_buf[4];
> +	u8 *iobuf;
>  };
>  
>  static inline struct tpm_tis_spi_phy *to_tpm_tis_spi_phy(struct tpm_tis_data *data)
> @@ -71,14 +69,14 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
>  	while (len) {
>  		transfer_len = min_t(u16, len, MAX_SPI_FRAMESIZE);
>  
> -		phy->tx_buf[0] = direction | (transfer_len - 1);
> -		phy->tx_buf[1] = 0xd4;
> -		phy->tx_buf[2] = addr >> 8;
> -		phy->tx_buf[3] = addr;
> +		phy->iobuf[0] = direction | (transfer_len - 1);
> +		phy->iobuf[1] = 0xd4;
> +		phy->iobuf[2] = addr >> 8;
> +		phy->iobuf[3] = addr;
>  
>  		memset(&spi_xfer, 0, sizeof(spi_xfer));
> -		spi_xfer.tx_buf = phy->tx_buf;
> -		spi_xfer.rx_buf = phy->rx_buf;
> +		spi_xfer.tx_buf = phy->iobuf;
> +		spi_xfer.rx_buf = phy->iobuf;
>  		spi_xfer.len = 4;
>  		spi_xfer.cs_change = 1;
>  
> @@ -88,9 +86,9 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
>  		if (ret < 0)
>  			goto exit;
>  
> -		if ((phy->rx_buf[3] & 0x01) == 0) {
> +		if ((phy->iobuf[3] & 0x01) == 0) {
>  			// handle SPI wait states
> -			phy->tx_buf[0] = 0;
> +			phy->iobuf[0] = 0;
>  
>  			for (i = 0; i < TPM_RETRY; i++) {
>  				spi_xfer.len = 1;
> @@ -99,7 +97,7 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
>  				ret = spi_sync_locked(phy->spi_device, &m);
>  				if (ret < 0)
>  					goto exit;
> -				if (phy->rx_buf[0] & 0x01)
> +				if (phy->iobuf[0] & 0x01)
>  					break;
>  			}
>  
> @@ -115,10 +113,9 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
>  
>  		if (direction) {
>  			spi_xfer.tx_buf = NULL;
> -			spi_xfer.rx_buf = buffer;
>  		} else {
> -			spi_xfer.tx_buf = buffer;
>  			spi_xfer.rx_buf = NULL;
> +			memcpy(phy->iobuf, buffer, transfer_len);
>  		}
>  
>  		spi_message_init(&m);
> @@ -127,6 +124,9 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
>  		if (ret < 0)
>  			goto exit;
>  
> +		if (direction)
> +			memcpy(buffer, phy->iobuf, transfer_len);
> +
>  		len -= transfer_len;
>  		buffer += transfer_len;
>  	}
> @@ -194,6 +194,10 @@ static int tpm_tis_spi_probe(struct spi_device *dev)
>  
>  	phy->spi_device = dev;
>  
> +	phy->iobuf = devm_kmalloc(&dev->dev, MAX_SPI_FRAMESIZE, GFP_KERNEL);
> +	if (!phy->iobuf)
> +		return -ENOMEM;
> +
>  	return tpm_tis_core_init(&dev->dev, &phy->priv, -1, &tpm_spi_phy_ops,
>  				 NULL);
>  }
> -- 
> 2.7.4
>