[PATCH v3 0/6] tpm_crb: Add command and response buffer chunking support

[PATCH v3 0/6] tpm_crb: Add command and response buffer chunking support

[Arun Menon]

The new version of TCG TPM v185 [1] supports sending data/commands in
chunks for the CRB (Command Response Buffer) interface. This is in line
with the initiative to support PQC algorithms.

This series implements the logic to send and receive larger TPM
cmd/rsp between the linux guest and the TPM backend in chunks.
Currently, the TPM CRB driver is limited by the physical size of the
MMIO window. When userspace attempts to send a payload that exceeds this
size, the driver rejects it.

This series introduces chunking support. The driver now checks the CRB
interface capability for CRB_INTF_CAP_CRB_CHUNK. If supported by the
backend, the driver will slice oversized commands into MMIO-sized
chunks, signalling the backend via CRB_START_NEXT_CHUNK, and finalizing
with CRB_START_INVOKE. Responses are also read back in a similar chunked
manner.

If the backend does not support chunking, the driver retains its legacy
behaviour and enforces the standard size limits.

This feature also requires the QEMU to interpret the data in chunks and
forward it to the TPM backend and subsequently dispatch the TPM response
in chunks back to the linux guest. This is implemented in [2]

This series depends on Jarkko's unmerged patch from the mailing list:
[PATCH v9 11/11] tpm-buf: Implement managed allocations.

Depends-on: <http://lore.kernel.org/20260125192526.782202-12-jarkko@kernel.org>

The whole series applied on top of for-next-tpm branch (with prerequisite)
can be found here:
https://github.com/armenon-rh/linux/tree/tpm-crb-linux

[1] https://trustedcomputinggroup.org/wp-content/uploads/PC-Client-Specific-Platform-TPM-Profile-for-TPM-2p0-v1p07_Pub.pdf
[2] https://lore.kernel.org/qemu-devel/20260506075813.120781-1-armenon@redhat.com/

v3
--
- Split patch 2, so that the code is cleaner.
- Re-order the buffer size adjustment patch.
- Rename crb_trigger_tpm to tpm_crb_start.
- Add dispatching logic in send and recv functions. Chunking is
  separated from no-chunking for clarity.
- Increase TPM_BUFSIZE in the common file include/linux/tpm.h following,
  [PATCH v9 11/11] tpm-buf: Implement managed allocations
  https://lore.kernel.org/linux-integrity/20260125192526.782202-12-jarkko@kernel.org/

v2
--
- Add size checks before copying memory.
- Update TPM_BUFSIZE to 8KB.
- Commit messages updated to indicate motivation and logic of the change.

Arun Menon (6):
  tpm_crb: Add register definitions of TPM CRB chunking fields
  tpm_crb: Split start method into a separate header
  tpm_crb: Add start_cmd parameter to tpm_crb_start wrapper
  tpm: tis_i2c: Use local 4KB buffer to limit memory usage
  tpm: Increase TPM_BUFSIZE to 8kB for chunking support
  tpm_crb: Implement command and response chunking logic

 drivers/char/tpm/tpm_crb.c     | 257 +++++++++++++++++++++++++--------
 drivers/char/tpm/tpm_tis_i2c.c |   6 +-
 include/linux/tpm.h            |   2 +-
 3 files changed, 204 insertions(+), 61 deletions(-)

-- 
2.54.0

[PATCH v3 1/6] tpm_crb: Add register definitions of TPM CRB chunking fields

[Arun Menon]

From: Arun Menon <armenon@redhat.com>

Post-quantum cryptographic (PQC) algorithms can require buffer sizes that
exceed the physical capacity of the TPM's Command/Response Buffer (CRB).
To support these larger payloads, the TPM 2.0 CRB specification [1]
allows for data chunking when the physical MMIO window is smaller than
the required buffer size.

To support this protocol, the TPM driver must be able to detect the
chunking capability, and signal the backend using specific start
method flags, also known as the control area start register bits.

As per sections 6.4.2.2 and 6.5.3.9 of the specification document [1]
Add 2 new bit flags to the existing enum crb_start and add the
capability bit.
- CRB_INTF_CAP_CRB_CHUNK: A capability bit used to detect if the backend
  supports chunking.
- CRB_START_NEXT_CHUNK: A control bit to signal the TPM to consume the
  current command buffer, or to get the next chunk from the response
  buffer.
- CRB_START_RESP_RETRY: A control bit to signal retransmission of a
  response buffer.

[1] https://trustedcomputinggroup.org/wp-content/uploads/PC-Client-Specific-Platform-TPM-Profile-for-TPM-2p0-v1p07_rc1_121225.pdf

Signed-off-by: Arun Menon <armenon@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
---
 drivers/char/tpm/tpm_crb.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
index ceb4100ba400..d76f9e30f036 100644
--- a/drivers/char/tpm/tpm_crb.c
+++ b/drivers/char/tpm/tpm_crb.c
@@ -57,12 +57,18 @@ enum crb_ctrl_sts {
 
 enum crb_start {
 	CRB_START_INVOKE	= BIT(0),
+	CRB_START_RESP_RETRY = BIT(1),
+	CRB_START_NEXT_CHUNK = BIT(2),
 };
 
 enum crb_cancel {
 	CRB_CANCEL_INVOKE	= BIT(0),
 };
 
+enum crb_intf {
+	CRB_INTF_CAP_CRB_CHUNK = BIT(10),
+};
+
 struct crb_regs_head {
 	u32 loc_state;
 	u32 reserved1;
-- 
2.54.0

[PATCH v3 2/6] tpm_crb: Split start method into a separate header

[Arun Menon]

From: Arun Menon <armenon@redhat.com>

The current implementation handles different platform start methods
(ACPI, ARM SMC, and ARM FFA) directly within crb_send().
Move this logic into a new helper function, tpm_crb_start(). This is a
pure refactor with no functional changes intended.

Signed-off-by: Arun Menon <armenon@redhat.com>
---
 drivers/char/tpm/tpm_crb.c | 50 ++++++++++++++++++++------------------
 1 file changed, 27 insertions(+), 23 deletions(-)

diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
index d76f9e30f036..9a2f512b4ae3 100644
--- a/drivers/char/tpm/tpm_crb.c
+++ b/drivers/char/tpm/tpm_crb.c
@@ -446,6 +446,32 @@ static int tpm_crb_smc_start(struct device *dev, unsigned long func_id)
 }
 #endif
 
+static int tpm_crb_start(struct tpm_chip *chip)
+{
+	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
+	int rc = 0;
+	/* The reason for the extra quirk is that the PTT in 4th Gen Core CPUs
+	 * report only ACPI start but in practice seems to require both
+	 * CRB start, hence invoking CRB start method if hid == MSFT0101.
+	 */
+	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER ||
+	    priv->sm == ACPI_TPM2_MEMORY_MAPPED ||
+	    !strcmp(priv->hid, "MSFT0101"))
+		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
+	if (priv->sm == ACPI_TPM2_START_METHOD ||
+	    priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_START_METHOD)
+		rc = crb_do_acpi_start(chip);
+	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_ARM_SMC) {
+		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
+		rc = tpm_crb_smc_start(&chip->dev, priv->smc_func_id);
+	}
+	if (priv->sm == ACPI_TPM2_CRB_WITH_ARM_FFA) {
+		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
+		rc = tpm_crb_ffa_start(CRB_FFA_START_TYPE_COMMAND, chip->locality);
+	}
+	return rc;
+}
+
 static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
 {
 	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
@@ -471,29 +497,7 @@ static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
 	/* Make sure that cmd is populated before issuing start. */
 	wmb();
 
-	/* The reason for the extra quirk is that the PTT in 4th Gen Core CPUs
-	 * report only ACPI start but in practice seems to require both
-	 * CRB start, hence invoking CRB start method if hid == MSFT0101.
-	 */
-	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER ||
-	    priv->sm == ACPI_TPM2_MEMORY_MAPPED ||
-	    !strcmp(priv->hid, "MSFT0101"))
-		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
-
-	if (priv->sm == ACPI_TPM2_START_METHOD ||
-	    priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_START_METHOD)
-		rc = crb_do_acpi_start(chip);
-
-	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_ARM_SMC) {
-		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
-		rc = tpm_crb_smc_start(&chip->dev, priv->smc_func_id);
-	}
-
-	if (priv->sm == ACPI_TPM2_CRB_WITH_ARM_FFA) {
-		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
-		rc = tpm_crb_ffa_start(CRB_FFA_START_TYPE_COMMAND, chip->locality);
-	}
-
+	rc = tpm_crb_start(chip);
 	if (rc)
 		return rc;
 
-- 
2.54.0

[PATCH v3 3/6] tpm_crb: Add start_cmd parameter to tpm_crb_start wrapper

[Arun Menon]

From: Arun Menon <armenon@redhat.com>

The current implementation of tpm_crb_start() is limited to triggering
the CRB_START_INVOKE bit. To support command and response chunking, the
driver must be able to send other control bits, like
CRB_START_NEXT_CHUNK, using the same platform-specific paths.

This commit adds the start_cmd parameter to tpm_crb_start() so the
caller can specify which command to send.

Signed-off-by: Arun Menon <armenon@redhat.com>
---
 drivers/char/tpm/tpm_crb.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
index 9a2f512b4ae3..31f530744e90 100644
--- a/drivers/char/tpm/tpm_crb.c
+++ b/drivers/char/tpm/tpm_crb.c
@@ -446,7 +446,7 @@ static int tpm_crb_smc_start(struct device *dev, unsigned long func_id)
 }
 #endif
 
-static int tpm_crb_start(struct tpm_chip *chip)
+static int tpm_crb_start(struct tpm_chip *chip, u32 start_cmd)
 {
 	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
 	int rc = 0;
@@ -457,16 +457,16 @@ static int tpm_crb_start(struct tpm_chip *chip)
 	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER ||
 	    priv->sm == ACPI_TPM2_MEMORY_MAPPED ||
 	    !strcmp(priv->hid, "MSFT0101"))
-		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
+		iowrite32(start_cmd, &priv->regs_t->ctrl_start);
 	if (priv->sm == ACPI_TPM2_START_METHOD ||
 	    priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_START_METHOD)
 		rc = crb_do_acpi_start(chip);
 	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_ARM_SMC) {
-		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
+		iowrite32(start_cmd, &priv->regs_t->ctrl_start);
 		rc = tpm_crb_smc_start(&chip->dev, priv->smc_func_id);
 	}
 	if (priv->sm == ACPI_TPM2_CRB_WITH_ARM_FFA) {
-		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
+		iowrite32(start_cmd, &priv->regs_t->ctrl_start);
 		rc = tpm_crb_ffa_start(CRB_FFA_START_TYPE_COMMAND, chip->locality);
 	}
 	return rc;
@@ -497,7 +497,7 @@ static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
 	/* Make sure that cmd is populated before issuing start. */
 	wmb();
 
-	rc = tpm_crb_start(chip);
+	rc = tpm_crb_start(chip, CRB_START_INVOKE);
 	if (rc)
 		return rc;
 
-- 
2.54.0

[PATCH v3 4/6] tpm: tis_i2c: Use local 4KB buffer to limit memory usage

[Arun Menon]

From: Arun Menon <armenon@redhat.com>

The global increase of TPM_BUFSIZE to 8KB is necessary to support
Post-Quantum Cryptography (PQC) payloads. However, applying this increase
to the tpm_tis_i2c driver is unnecessary and wasteful due to physical
transport limitations as pointed out in [1]

This commit introduces a local buffer limit that is used in the i2c
driver.

[1] https://sashiko.dev/#/patchset/20260324071803.324774-1-armenon%40redhat.com?patch=8319

Signed-off-by: Arun Menon <armenon@redhat.com>
---
 drivers/char/tpm/tpm_tis_i2c.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
index 6cd07dd34507..db19d459ea1e 100644
--- a/drivers/char/tpm/tpm_tis_i2c.c
+++ b/drivers/char/tpm/tpm_tis_i2c.c
@@ -54,6 +54,8 @@
 #define TPM_INTF_CAPABILITY_ZERO 0x0FFFF000
 #define TPM_I2C_INTERFACE_CAPABILITY_ZERO 0x80000000
 
+#define TPM_I2C_BUFSIZE 4096
+
 struct tpm_tis_i2c_phy {
 	struct tpm_tis_data priv;
 	struct i2c_client *i2c_client;
@@ -232,7 +234,7 @@ static int tpm_tis_i2c_write_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
 	int ret;
 	u16 wrote = 0;
 
-	if (len > TPM_BUFSIZE - 1)
+	if (len > TPM_I2C_BUFSIZE - 1)
 		return -EIO;
 
 	phy->io_buf[0] = reg;
@@ -339,7 +341,7 @@ static int tpm_tis_i2c_probe(struct i2c_client *dev)
 	if (!phy)
 		return -ENOMEM;
 
-	phy->io_buf = devm_kzalloc(&dev->dev, TPM_BUFSIZE, GFP_KERNEL);
+	phy->io_buf = devm_kzalloc(&dev->dev, TPM_I2C_BUFSIZE, GFP_KERNEL);
 	if (!phy->io_buf)
 		return -ENOMEM;
 
-- 
2.54.0

[PATCH v3 5/6] tpm: Increase TPM_BUFSIZE to 8kB for chunking support

[Arun Menon]

From: Arun Menon <armenon@redhat.com>

The size of the command is checked against TPM_BUFSIZE early on before
even sending it to the backend. We therefore need to increase the
TPM_BUFSIZE to allow support for larger commands.

For now, 8KB seems sufficient for ML-KEM and ML-DSA algorithms and it is
also order-1 safe.

Signed-off-by: Arun Menon <armenon@redhat.com>
---
 include/linux/tpm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 01216156a1ec..af2bfac45fe0 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -26,7 +26,7 @@
 #include <crypto/aes.h>
 
 #define TPM_DIGEST_SIZE		20	/* Max TPM v1.2 PCR size */
-#define TPM_BUFSIZE		4096
+#define TPM_BUFSIZE		8192
 
 /*
  * SHA-512 is, as of today, the largest digest in the TCG algorithm repository.
-- 
2.54.0

[PATCH v3 6/6] tpm_crb: Implement command and response chunking logic

[Arun Menon]

From: Arun Menon <armenon@redhat.com>

With the introduction of support for Post Quantum Cryptography
algorithms in TPM, the commands and responses will grow in size.
Some TPMs have a physical hardware memory window (MMIO) that is
smaller than the commands we need to send. Therefore this commit
implements the core logic of sending/receiving data in chunks.

Instead of sending the whole command at once, the driver now sends it in
small chunks. After each chunk, it signals the TPM using a nextChunk
signal, and waits for the TPM to consume the data. Once the final piece
is delivered, the driver signals the TPM to begin execution by toggling
the start invoke bit. We use the same logic in reverse to read large
responses from the TPM.

This allows the driver to handle large payloads even when the hardware
interface has limited memory. This kernel-side support corresponds to
the backend implementation in QEMU [1]. QEMU reassembles the chunks
before passing them to the TPM emulator.

[1] https://lore.kernel.org/qemu-devel/20260506075813.120781-1-armenon@redhat.com/

Signed-off-by: Arun Menon <armenon@redhat.com>
---
 drivers/char/tpm/tpm_crb.c | 215 +++++++++++++++++++++++++++++--------
 1 file changed, 173 insertions(+), 42 deletions(-)

diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
index 31f530744e90..8b2aaa109fc4 100644
--- a/drivers/char/tpm/tpm_crb.c
+++ b/drivers/char/tpm/tpm_crb.c
@@ -105,11 +105,13 @@ struct crb_priv {
 	u8 __iomem *cmd;
 	u8 __iomem *rsp;
 	u32 cmd_size;
+	u32 rsp_size;
 	u32 smc_func_id;
 	u32 __iomem *pluton_start_addr;
 	u32 __iomem *pluton_reply_addr;
 	u8 ffa_flags;
 	u8 ffa_attributes;
+	u32 intf_id;
 };
 
 struct tpm2_crb_smc {
@@ -369,38 +371,6 @@ static u8 crb_status(struct tpm_chip *chip)
 	return sts;
 }
 
-static int crb_recv(struct tpm_chip *chip, u8 *buf, size_t count)
-{
-	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
-	unsigned int expected;
-
-	/* A sanity check that the upper layer wants to get at least the header
-	 * as that is the minimum size for any TPM response.
-	 */
-	if (count < TPM_HEADER_SIZE)
-		return -EIO;
-
-	/* If this bit is set, according to the spec, the TPM is in
-	 * unrecoverable condition.
-	 */
-	if (ioread32(&priv->regs_t->ctrl_sts) & CRB_CTRL_STS_ERROR)
-		return -EIO;
-
-	/* Read the first 8 bytes in order to get the length of the response.
-	 * We read exactly a quad word in order to make sure that the remaining
-	 * reads will be aligned.
-	 */
-	memcpy_fromio(buf, priv->rsp, 8);
-
-	expected = be32_to_cpup((__be32 *)&buf[2]);
-	if (expected > count || expected < TPM_HEADER_SIZE)
-		return -EIO;
-
-	memcpy_fromio(&buf[8], &priv->rsp[8], expected - 8);
-
-	return expected;
-}
-
 static int crb_do_acpi_start(struct tpm_chip *chip)
 {
 	union acpi_object *obj;
@@ -472,17 +442,71 @@ static int tpm_crb_start(struct tpm_chip *chip, u32 start_cmd)
 	return rc;
 }
 
+static int tpm_crb_send_no_chunks(struct tpm_chip *chip, u8 *buf, size_t len)
+{
+	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
+	int rc;
+
+	memcpy_toio(priv->cmd, buf, len);
+
+	/* Make sure that cmd is populated before issuing start. */
+	wmb();
+
+	rc = tpm_crb_start(chip, CRB_START_INVOKE);
+	if (rc)
+		return rc;
+
+	return crb_try_pluton_doorbell(priv, false);
+}
+
+static int tpm_crb_send_chunks(struct tpm_chip *chip, u8 *buf, size_t len)
+{
+	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
+	size_t offset = 0;
+	size_t chunk_size;
+	int rc;
+
+	while (offset < len) {
+		chunk_size = min_t(size_t, len - offset, priv->cmd_size);
+
+		if (chunk_size == 0)
+			break;
+
+		memcpy_toio(priv->cmd, buf + offset, chunk_size);
+		offset += chunk_size;
+
+		/* Make sure that cmd is populated before issuing start. */
+		wmb();
+		if (offset < len) {
+			rc = tpm_crb_start(chip, CRB_START_NEXT_CHUNK);
+			if (rc)
+				return rc;
+			if (!crb_wait_for_reg_32(&priv->regs_t->ctrl_start,
+									 CRB_START_NEXT_CHUNK, 0,
+									 TPM2_TIMEOUT_C)) {
+				dev_err(&chip->dev,
+						"Timeout waiting for backend to consume chunk\n");
+				return -ETIME;
+			}
+		} else {
+			rc = tpm_crb_start(chip, CRB_START_INVOKE);
+			if (rc)
+				return rc;
+		}
+	}
+
+	return crb_try_pluton_doorbell(priv, false);
+}
 static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
 {
 	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
-	int rc = 0;
 
 	/* Zero the cancel register so that the next command will not get
 	 * canceled.
 	 */
 	iowrite32(0, &priv->regs_t->ctrl_cancel);
 
-	if (len > priv->cmd_size) {
+	if (len > priv->cmd_size && !(priv->intf_id & CRB_INTF_CAP_CRB_CHUNK)) {
 		dev_err(&chip->dev, "invalid command count value %zd %d\n",
 			len, priv->cmd_size);
 		return -E2BIG;
@@ -492,16 +516,115 @@ static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
 	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_PLUTON)
 		__crb_cmd_ready(&chip->dev, priv, chip->locality);
 
-	memcpy_toio(priv->cmd, buf, len);
+	if (len <= priv->cmd_size)
+		return tpm_crb_send_no_chunks(chip, buf, len);
 
-	/* Make sure that cmd is populated before issuing start. */
-	wmb();
+	return tpm_crb_send_chunks(chip, buf, len);
+}
 
-	rc = tpm_crb_start(chip, CRB_START_INVOKE);
-	if (rc)
-		return rc;
+static int tpm_crb_recv_no_chunks(struct tpm_chip *chip, u8 *buf, size_t count)
+{
+	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
+	unsigned int expected;
 
-	return crb_try_pluton_doorbell(priv, false);
+	/* Read the first 8 bytes in order to get the length of the response.
+	 * We read exactly a quad word in order to make sure that the remaining
+	 * reads will be aligned.
+	 */
+	memcpy_fromio(buf, priv->rsp, 8);
+
+	expected = be32_to_cpup((__be32 *)&buf[2]);
+	if (expected > count || expected < TPM_HEADER_SIZE)
+		return -EIO;
+
+	memcpy_fromio(&buf[8], &priv->rsp[8], expected - 8);
+
+	return expected;
+}
+
+static int tpm_crb_recv_chunks(struct tpm_chip *chip, u8 *buf, size_t count,
+							   unsigned int expected)
+{
+	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
+	size_t offset = 0;
+	size_t chunk_size;
+	size_t first_read;
+	int rc;
+
+	if (expected > count)
+		return -EIO;
+	/*
+	 * Set chunk_size by comparing the size of the buffer that the upper
+	 * layer has allocated (count) to the hardware tpm limit (priv->rsp_size).
+	 * This is to prevent buffer overflow while writing to buf.
+	 */
+	chunk_size = min_t(size_t, count, priv->rsp_size);
+	if (chunk_size < 8)
+		return -EIO;
+
+	memcpy_fromio(buf, priv->rsp, 8);
+
+	/*
+	 * Compare the actual size of the response we found in
+	 * the header to the chunk size
+	 */
+	first_read = min_t(size_t, expected, chunk_size);
+
+	memcpy_fromio(&buf[8], &priv->rsp[8], first_read - 8);
+	offset = first_read;
+
+	while (offset < expected) {
+		rc = tpm_crb_start(chip, CRB_START_NEXT_CHUNK);
+		if (rc)
+			return rc;
+
+		if (!crb_wait_for_reg_32(&priv->regs_t->ctrl_start,
+								 CRB_START_NEXT_CHUNK, 0,
+								 TPM2_TIMEOUT_C)) {
+			dev_err(&chip->dev, "Timeout waiting for backend response\n");
+			return -ETIME;
+		}
+
+		chunk_size = min_t(size_t, expected - offset, priv->rsp_size);
+		memcpy_fromio(buf + offset, priv->rsp, chunk_size);
+		offset += chunk_size;
+	}
+
+	return expected;
+}
+
+static int crb_recv(struct tpm_chip *chip, u8 *buf, size_t count)
+{
+	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
+	unsigned int expected;
+
+	/* A sanity check that the upper layer wants to get at least the header
+	 * as that is the minimum size for any TPM response.
+	 */
+	if (count < TPM_HEADER_SIZE)
+		return -EIO;
+
+	/* If this bit is set, according to the spec, the TPM is in
+	 * unrecoverable condition.
+	 */
+	if (ioread32(&priv->regs_t->ctrl_sts) & CRB_CTRL_STS_ERROR)
+		return -EIO;
+
+	/*
+	 * Peek at the first 8 bytes to determine the response size
+	 */
+	expected = be32_to_cpup((__be32 *)&priv->rsp[2]);
+
+	if (expected <= priv->rsp_size)
+		return tpm_crb_recv_no_chunks(chip, buf, count);
+
+	if (!(priv->intf_id & CRB_INTF_CAP_CRB_CHUNK)) {
+		dev_err(&chip->dev,
+			    "Response larger than MMIO and chunking not supported\n");
+		return -EIO;
+	}
+
+	return tpm_crb_recv_chunks(chip, buf, count, expected);
 }
 
 static void crb_cancel(struct tpm_chip *chip)
@@ -728,6 +851,12 @@ static int crb_map_io(struct device *dev, struct crb_priv *priv,
 		goto out;
 	}
 
+	if (priv->regs_h)
+		priv->intf_id = ioread32((u32 __iomem *)&priv->regs_h->intf_id);
+
+	if (priv->intf_id & CRB_INTF_CAP_CRB_CHUNK)
+		dev_info(dev, "CRB Chunking is supported by backend\n");
+
 	memcpy_fromio(&__rsp_pa, &priv->regs_t->ctrl_rsp_pa, 8);
 	rsp_pa = le64_to_cpu(__rsp_pa);
 	rsp_size = ioread32(&priv->regs_t->ctrl_rsp_size);
@@ -765,8 +894,10 @@ static int crb_map_io(struct device *dev, struct crb_priv *priv,
 	priv->rsp = priv->cmd;
 
 out:
-	if (!ret)
+	if (!ret) {
 		priv->cmd_size = cmd_size;
+		priv->rsp_size = rsp_size;
+	}
 
 	__crb_go_idle(dev, priv, 0);
 
-- 
2.54.0

Re: [PATCH v3 0/6] tpm_crb: Add command and response buffer chunking support

[Jarkko Sakkinen]

On Mon, May 18, 2026 at 08:47:18PM +0530, Arun Menon wrote:
> The new version of TCG TPM v185 [1] supports sending data/commands in
> chunks for the CRB (Command Response Buffer) interface. This is in line
> with the initiative to support PQC algorithms.
> 
> This series implements the logic to send and receive larger TPM
> cmd/rsp between the linux guest and the TPM backend in chunks.
> Currently, the TPM CRB driver is limited by the physical size of the
> MMIO window. When userspace attempts to send a payload that exceeds this
> size, the driver rejects it.
> 
> This series introduces chunking support. The driver now checks the CRB
> interface capability for CRB_INTF_CAP_CRB_CHUNK. If supported by the
> backend, the driver will slice oversized commands into MMIO-sized
> chunks, signalling the backend via CRB_START_NEXT_CHUNK, and finalizing
> with CRB_START_INVOKE. Responses are also read back in a similar chunked
> manner.
> 
> If the backend does not support chunking, the driver retains its legacy
> behaviour and enforces the standard size limits.
> 
> This feature also requires the QEMU to interpret the data in chunks and
> forward it to the TPM backend and subsequently dispatch the TPM response
> in chunks back to the linux guest. This is implemented in [2]
> 
> This series depends on Jarkko's unmerged patch from the mailing list:
> [PATCH v9 11/11] tpm-buf: Implement managed allocations.
> 
> Depends-on: <http://lore.kernel.org/20260125192526.782202-12-jarkko@kernel.org>

I'll rebase this to the latest master so that it can be included to the
series.

> 
> The whole series applied on top of for-next-tpm branch (with prerequisite)
> can be found here:
> https://github.com/armenon-rh/linux/tree/tpm-crb-linux
> 
> [1] https://trustedcomputinggroup.org/wp-content/uploads/PC-Client-Specific-Platform-TPM-Profile-for-TPM-2p0-v1p07_Pub.pdf
> [2] https://lore.kernel.org/qemu-devel/20260506075813.120781-1-armenon@redhat.com/
> 
> v3
> --
> - Split patch 2, so that the code is cleaner.
> - Re-order the buffer size adjustment patch.
> - Rename crb_trigger_tpm to tpm_crb_start.
> - Add dispatching logic in send and recv functions. Chunking is
>   separated from no-chunking for clarity.
> - Increase TPM_BUFSIZE in the common file include/linux/tpm.h following,
>   [PATCH v9 11/11] tpm-buf: Implement managed allocations
>   https://lore.kernel.org/linux-integrity/20260125192526.782202-12-jarkko@kernel.org/
> 
> v2
> --
> - Add size checks before copying memory.
> - Update TPM_BUFSIZE to 8KB.
> - Commit messages updated to indicate motivation and logic of the change.
> 
> Arun Menon (6):
>   tpm_crb: Add register definitions of TPM CRB chunking fields
>   tpm_crb: Split start method into a separate header
>   tpm_crb: Add start_cmd parameter to tpm_crb_start wrapper
>   tpm: tis_i2c: Use local 4KB buffer to limit memory usage
>   tpm: Increase TPM_BUFSIZE to 8kB for chunking support
>   tpm_crb: Implement command and response chunking logic
> 
>  drivers/char/tpm/tpm_crb.c     | 257 +++++++++++++++++++++++++--------
>  drivers/char/tpm/tpm_tis_i2c.c |   6 +-
>  include/linux/tpm.h            |   2 +-
>  3 files changed, 204 insertions(+), 61 deletions(-)
> 
> -- 
> 2.54.0
> 

BR, Jarkko

Re: [PATCH v3 3/6] tpm_crb: Add start_cmd parameter to tpm_crb_start wrapper

[Jarkko Sakkinen]

On Mon, May 18, 2026 at 08:47:21PM +0530, Arun Menon wrote:
> From: Arun Menon <armenon@redhat.com>
> 
> The current implementation of tpm_crb_start() is limited to triggering
> the CRB_START_INVOKE bit. To support command and response chunking, the
> driver must be able to send other control bits, like
> CRB_START_NEXT_CHUNK, using the same platform-specific paths.
> 
> This commit adds the start_cmd parameter to tpm_crb_start() so the
> caller can specify which command to send.
> 
> Signed-off-by: Arun Menon <armenon@redhat.com>
> ---
>  drivers/char/tpm/tpm_crb.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
> index 9a2f512b4ae3..31f530744e90 100644
> --- a/drivers/char/tpm/tpm_crb.c
> +++ b/drivers/char/tpm/tpm_crb.c
> @@ -446,7 +446,7 @@ static int tpm_crb_smc_start(struct device *dev, unsigned long func_id)
>  }
>  #endif
>  
> -static int tpm_crb_start(struct tpm_chip *chip)
> +static int tpm_crb_start(struct tpm_chip *chip, u32 start_cmd)
>  {
>  	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
>  	int rc = 0;
> @@ -457,16 +457,16 @@ static int tpm_crb_start(struct tpm_chip *chip)
>  	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER ||
>  	    priv->sm == ACPI_TPM2_MEMORY_MAPPED ||
>  	    !strcmp(priv->hid, "MSFT0101"))
> -		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> +		iowrite32(start_cmd, &priv->regs_t->ctrl_start);
>  	if (priv->sm == ACPI_TPM2_START_METHOD ||
>  	    priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_START_METHOD)
>  		rc = crb_do_acpi_start(chip);
>  	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_ARM_SMC) {
> -		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> +		iowrite32(start_cmd, &priv->regs_t->ctrl_start);
>  		rc = tpm_crb_smc_start(&chip->dev, priv->smc_func_id);
>  	}
>  	if (priv->sm == ACPI_TPM2_CRB_WITH_ARM_FFA) {
> -		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> +		iowrite32(start_cmd, &priv->regs_t->ctrl_start);
>  		rc = tpm_crb_ffa_start(CRB_FFA_START_TYPE_COMMAND, chip->locality);
>  	}
>  	return rc;
> @@ -497,7 +497,7 @@ static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
>  	/* Make sure that cmd is populated before issuing start. */
>  	wmb();
>  
> -	rc = tpm_crb_start(chip);
> +	rc = tpm_crb_start(chip, CRB_START_INVOKE);
>  	if (rc)
>  		return rc;
>  
> -- 
> 2.54.0
> 

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko

Re: [PATCH v3 2/6] tpm_crb: Split start method into a separate header

[Jarkko Sakkinen]

On Mon, May 18, 2026 at 08:47:20PM +0530, Arun Menon wrote:
> From: Arun Menon <armenon@redhat.com>
> 
> The current implementation handles different platform start methods
> (ACPI, ARM SMC, and ARM FFA) directly within crb_send().
> Move this logic into a new helper function, tpm_crb_start(). This is a
> pure refactor with no functional changes intended.
> 
> Signed-off-by: Arun Menon <armenon@redhat.com>
> ---
>  drivers/char/tpm/tpm_crb.c | 50 ++++++++++++++++++++------------------
>  1 file changed, 27 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
> index d76f9e30f036..9a2f512b4ae3 100644
> --- a/drivers/char/tpm/tpm_crb.c
> +++ b/drivers/char/tpm/tpm_crb.c
> @@ -446,6 +446,32 @@ static int tpm_crb_smc_start(struct device *dev, unsigned long func_id)
>  }
>  #endif
>  
> +static int tpm_crb_start(struct tpm_chip *chip)
> +{
> +	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> +	int rc = 0;
> +	/* The reason for the extra quirk is that the PTT in 4th Gen Core CPUs
> +	 * report only ACPI start but in practice seems to require both
> +	 * CRB start, hence invoking CRB start method if hid == MSFT0101.
> +	 */
> +	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER ||
> +	    priv->sm == ACPI_TPM2_MEMORY_MAPPED ||
> +	    !strcmp(priv->hid, "MSFT0101"))
> +		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> +	if (priv->sm == ACPI_TPM2_START_METHOD ||
> +	    priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_START_METHOD)
> +		rc = crb_do_acpi_start(chip);
> +	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_ARM_SMC) {
> +		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> +		rc = tpm_crb_smc_start(&chip->dev, priv->smc_func_id);
> +	}
> +	if (priv->sm == ACPI_TPM2_CRB_WITH_ARM_FFA) {
> +		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> +		rc = tpm_crb_ffa_start(CRB_FFA_START_TYPE_COMMAND, chip->locality);
> +	}
> +	return rc;
> +}
> +
>  static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
>  {
>  	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> @@ -471,29 +497,7 @@ static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
>  	/* Make sure that cmd is populated before issuing start. */
>  	wmb();
>  
> -	/* The reason for the extra quirk is that the PTT in 4th Gen Core CPUs
> -	 * report only ACPI start but in practice seems to require both
> -	 * CRB start, hence invoking CRB start method if hid == MSFT0101.
> -	 */
> -	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER ||
> -	    priv->sm == ACPI_TPM2_MEMORY_MAPPED ||
> -	    !strcmp(priv->hid, "MSFT0101"))
> -		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> -
> -	if (priv->sm == ACPI_TPM2_START_METHOD ||
> -	    priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_START_METHOD)
> -		rc = crb_do_acpi_start(chip);
> -
> -	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_ARM_SMC) {
> -		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> -		rc = tpm_crb_smc_start(&chip->dev, priv->smc_func_id);
> -	}
> -
> -	if (priv->sm == ACPI_TPM2_CRB_WITH_ARM_FFA) {
> -		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> -		rc = tpm_crb_ffa_start(CRB_FFA_START_TYPE_COMMAND, chip->locality);
> -	}
> -
> +	rc = tpm_crb_start(chip);
>  	if (rc)
>  		return rc;
>  
> -- 
> 2.54.0
> 


Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko

Re: [PATCH v3 4/6] tpm: tis_i2c: Use local 4KB buffer to limit memory usage

[Jarkko Sakkinen]

On Mon, May 18, 2026 at 08:47:22PM +0530, Arun Menon wrote:
> From: Arun Menon <armenon@redhat.com>
> 
> The global increase of TPM_BUFSIZE to 8KB is necessary to support
> Post-Quantum Cryptography (PQC) payloads. However, applying this increase
> to the tpm_tis_i2c driver is unnecessary and wasteful due to physical
> transport limitations as pointed out in [1]
> 
> This commit introduces a local buffer limit that is used in the i2c
> driver.
> 
> [1] https://sashiko.dev/#/patchset/20260324071803.324774-1-armenon%40redhat.com?patch=8319
> 
> Signed-off-by: Arun Menon <armenon@redhat.com>
> ---
>  drivers/char/tpm/tpm_tis_i2c.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
> index 6cd07dd34507..db19d459ea1e 100644
> --- a/drivers/char/tpm/tpm_tis_i2c.c
> +++ b/drivers/char/tpm/tpm_tis_i2c.c
> @@ -54,6 +54,8 @@
>  #define TPM_INTF_CAPABILITY_ZERO 0x0FFFF000
>  #define TPM_I2C_INTERFACE_CAPABILITY_ZERO 0x80000000
>  
> +#define TPM_I2C_BUFSIZE 4096
> +
>  struct tpm_tis_i2c_phy {
>  	struct tpm_tis_data priv;
>  	struct i2c_client *i2c_client;
> @@ -232,7 +234,7 @@ static int tpm_tis_i2c_write_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
>  	int ret;
>  	u16 wrote = 0;
>  
> -	if (len > TPM_BUFSIZE - 1)
> +	if (len > TPM_I2C_BUFSIZE - 1)
>  		return -EIO;
>  
>  	phy->io_buf[0] = reg;
> @@ -339,7 +341,7 @@ static int tpm_tis_i2c_probe(struct i2c_client *dev)
>  	if (!phy)
>  		return -ENOMEM;
>  
> -	phy->io_buf = devm_kzalloc(&dev->dev, TPM_BUFSIZE, GFP_KERNEL);
> +	phy->io_buf = devm_kzalloc(&dev->dev, TPM_I2C_BUFSIZE, GFP_KERNEL);
>  	if (!phy->io_buf)
>  		return -ENOMEM;
>  
> -- 
> 2.54.0
> 


Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko

Re: [PATCH v3 6/6] tpm_crb: Implement command and response chunking logic

[Jarkko Sakkinen]

On Mon, May 18, 2026 at 08:47:24PM +0530, Arun Menon wrote:
> From: Arun Menon <armenon@redhat.com>
> 
> With the introduction of support for Post Quantum Cryptography
> algorithms in TPM, the commands and responses will grow in size.
> Some TPMs have a physical hardware memory window (MMIO) that is
> smaller than the commands we need to send. Therefore this commit
> implements the core logic of sending/receiving data in chunks.
> 
> Instead of sending the whole command at once, the driver now sends it in
> small chunks. After each chunk, it signals the TPM using a nextChunk
> signal, and waits for the TPM to consume the data. Once the final piece
> is delivered, the driver signals the TPM to begin execution by toggling
> the start invoke bit. We use the same logic in reverse to read large
> responses from the TPM.
> 
> This allows the driver to handle large payloads even when the hardware
> interface has limited memory. This kernel-side support corresponds to
> the backend implementation in QEMU [1]. QEMU reassembles the chunks
> before passing them to the TPM emulator.
> 
> [1] https://lore.kernel.org/qemu-devel/20260506075813.120781-1-armenon@redhat.com/
> 
> Signed-off-by: Arun Menon <armenon@redhat.com>
> ---
>  drivers/char/tpm/tpm_crb.c | 215 +++++++++++++++++++++++++++++--------
>  1 file changed, 173 insertions(+), 42 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
> index 31f530744e90..8b2aaa109fc4 100644
> --- a/drivers/char/tpm/tpm_crb.c
> +++ b/drivers/char/tpm/tpm_crb.c
> @@ -105,11 +105,13 @@ struct crb_priv {
>  	u8 __iomem *cmd;
>  	u8 __iomem *rsp;
>  	u32 cmd_size;
> +	u32 rsp_size;
>  	u32 smc_func_id;
>  	u32 __iomem *pluton_start_addr;
>  	u32 __iomem *pluton_reply_addr;
>  	u8 ffa_flags;
>  	u8 ffa_attributes;
> +	u32 intf_id;
>  };
>  
>  struct tpm2_crb_smc {
> @@ -369,38 +371,6 @@ static u8 crb_status(struct tpm_chip *chip)
>  	return sts;
>  }
>  
> -static int crb_recv(struct tpm_chip *chip, u8 *buf, size_t count)
> -{
> -	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> -	unsigned int expected;
> -
> -	/* A sanity check that the upper layer wants to get at least the header
> -	 * as that is the minimum size for any TPM response.
> -	 */
> -	if (count < TPM_HEADER_SIZE)
> -		return -EIO;
> -
> -	/* If this bit is set, according to the spec, the TPM is in
> -	 * unrecoverable condition.
> -	 */
> -	if (ioread32(&priv->regs_t->ctrl_sts) & CRB_CTRL_STS_ERROR)
> -		return -EIO;
> -
> -	/* Read the first 8 bytes in order to get the length of the response.
> -	 * We read exactly a quad word in order to make sure that the remaining
> -	 * reads will be aligned.
> -	 */
> -	memcpy_fromio(buf, priv->rsp, 8);
> -
> -	expected = be32_to_cpup((__be32 *)&buf[2]);
> -	if (expected > count || expected < TPM_HEADER_SIZE)
> -		return -EIO;
> -
> -	memcpy_fromio(&buf[8], &priv->rsp[8], expected - 8);
> -
> -	return expected;
> -}
> -
>  static int crb_do_acpi_start(struct tpm_chip *chip)
>  {
>  	union acpi_object *obj;
> @@ -472,17 +442,71 @@ static int tpm_crb_start(struct tpm_chip *chip, u32 start_cmd)
>  	return rc;
>  }
>  
> +static int tpm_crb_send_no_chunks(struct tpm_chip *chip, u8 *buf, size_t len)
> +{
> +	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> +	int rc;
> +
> +	memcpy_toio(priv->cmd, buf, len);
> +
> +	/* Make sure that cmd is populated before issuing start. */
> +	wmb();
> +
> +	rc = tpm_crb_start(chip, CRB_START_INVOKE);
> +	if (rc)
> +		return rc;
> +
> +	return crb_try_pluton_doorbell(priv, false);
> +}
> +
> +static int tpm_crb_send_chunks(struct tpm_chip *chip, u8 *buf, size_t len)
> +{
> +	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> +	size_t offset = 0;
> +	size_t chunk_size;
> +	int rc;
> +
> +	while (offset < len) {
> +		chunk_size = min_t(size_t, len - offset, priv->cmd_size);
> +
> +		if (chunk_size == 0)
> +			break;
> +
> +		memcpy_toio(priv->cmd, buf + offset, chunk_size);
> +		offset += chunk_size;
> +
> +		/* Make sure that cmd is populated before issuing start. */
> +		wmb();
> +		if (offset < len) {
> +			rc = tpm_crb_start(chip, CRB_START_NEXT_CHUNK);
> +			if (rc)
> +				return rc;
> +			if (!crb_wait_for_reg_32(&priv->regs_t->ctrl_start,
> +									 CRB_START_NEXT_CHUNK, 0,
> +									 TPM2_TIMEOUT_C)) {
> +				dev_err(&chip->dev,
> +						"Timeout waiting for backend to consume chunk\n");
> +				return -ETIME;
> +			}
> +		} else {
> +			rc = tpm_crb_start(chip, CRB_START_INVOKE);
> +			if (rc)
> +				return rc;
> +		}
> +	}
> +
> +	return crb_try_pluton_doorbell(priv, false);
> +}
>  static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
>  {
>  	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> -	int rc = 0;
>  
>  	/* Zero the cancel register so that the next command will not get
>  	 * canceled.
>  	 */
>  	iowrite32(0, &priv->regs_t->ctrl_cancel);
>  
> -	if (len > priv->cmd_size) {
> +	if (len > priv->cmd_size && !(priv->intf_id & CRB_INTF_CAP_CRB_CHUNK)) {
>  		dev_err(&chip->dev, "invalid command count value %zd %d\n",
>  			len, priv->cmd_size);
>  		return -E2BIG;
> @@ -492,16 +516,115 @@ static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
>  	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_PLUTON)
>  		__crb_cmd_ready(&chip->dev, priv, chip->locality);
>  
> -	memcpy_toio(priv->cmd, buf, len);
> +	if (len <= priv->cmd_size)
> +		return tpm_crb_send_no_chunks(chip, buf, len);
>  
> -	/* Make sure that cmd is populated before issuing start. */
> -	wmb();
> +	return tpm_crb_send_chunks(chip, buf, len);
> +}
>  
> -	rc = tpm_crb_start(chip, CRB_START_INVOKE);
> -	if (rc)
> -		return rc;
> +static int tpm_crb_recv_no_chunks(struct tpm_chip *chip, u8 *buf, size_t count)
> +{
> +	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> +	unsigned int expected;
>  
> -	return crb_try_pluton_doorbell(priv, false);
> +	/* Read the first 8 bytes in order to get the length of the response.
> +	 * We read exactly a quad word in order to make sure that the remaining
> +	 * reads will be aligned.
> +	 */
> +	memcpy_fromio(buf, priv->rsp, 8);
> +
> +	expected = be32_to_cpup((__be32 *)&buf[2]);
> +	if (expected > count || expected < TPM_HEADER_SIZE)
> +		return -EIO;
> +
> +	memcpy_fromio(&buf[8], &priv->rsp[8], expected - 8);
> +
> +	return expected;
> +}
> +
> +static int tpm_crb_recv_chunks(struct tpm_chip *chip, u8 *buf, size_t count,
> +							   unsigned int expected)
> +{
> +	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> +	size_t offset = 0;
> +	size_t chunk_size;
> +	size_t first_read;
> +	int rc;
> +
> +	if (expected > count)
> +		return -EIO;
> +	/*
> +	 * Set chunk_size by comparing the size of the buffer that the upper
> +	 * layer has allocated (count) to the hardware tpm limit (priv->rsp_size).
> +	 * This is to prevent buffer overflow while writing to buf.
> +	 */
> +	chunk_size = min_t(size_t, count, priv->rsp_size);
> +	if (chunk_size < 8)
> +		return -EIO;
> +
> +	memcpy_fromio(buf, priv->rsp, 8);
> +
> +	/*
> +	 * Compare the actual size of the response we found in
> +	 * the header to the chunk size
> +	 */
> +	first_read = min_t(size_t, expected, chunk_size);
> +
> +	memcpy_fromio(&buf[8], &priv->rsp[8], first_read - 8);
> +	offset = first_read;
> +
> +	while (offset < expected) {
> +		rc = tpm_crb_start(chip, CRB_START_NEXT_CHUNK);
> +		if (rc)
> +			return rc;
> +
> +		if (!crb_wait_for_reg_32(&priv->regs_t->ctrl_start,
> +								 CRB_START_NEXT_CHUNK, 0,
> +								 TPM2_TIMEOUT_C)) {
> +			dev_err(&chip->dev, "Timeout waiting for backend response\n");
> +			return -ETIME;
> +		}
> +
> +		chunk_size = min_t(size_t, expected - offset, priv->rsp_size);
> +		memcpy_fromio(buf + offset, priv->rsp, chunk_size);
> +		offset += chunk_size;
> +	}
> +
> +	return expected;
> +}
> +
> +static int crb_recv(struct tpm_chip *chip, u8 *buf, size_t count)
> +{
> +	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> +	unsigned int expected;
> +
> +	/* A sanity check that the upper layer wants to get at least the header
> +	 * as that is the minimum size for any TPM response.
> +	 */
> +	if (count < TPM_HEADER_SIZE)
> +		return -EIO;
> +
> +	/* If this bit is set, according to the spec, the TPM is in
> +	 * unrecoverable condition.
> +	 */
> +	if (ioread32(&priv->regs_t->ctrl_sts) & CRB_CTRL_STS_ERROR)
> +		return -EIO;
> +
> +	/*
> +	 * Peek at the first 8 bytes to determine the response size
> +	 */
> +	expected = be32_to_cpup((__be32 *)&priv->rsp[2]);
> +
> +	if (expected <= priv->rsp_size)
> +		return tpm_crb_recv_no_chunks(chip, buf, count);
> +
> +	if (!(priv->intf_id & CRB_INTF_CAP_CRB_CHUNK)) {
> +		dev_err(&chip->dev,
> +			    "Response larger than MMIO and chunking not supported\n");
> +		return -EIO;
> +	}
> +
> +	return tpm_crb_recv_chunks(chip, buf, count, expected);
>  }
>  
>  static void crb_cancel(struct tpm_chip *chip)
> @@ -728,6 +851,12 @@ static int crb_map_io(struct device *dev, struct crb_priv *priv,
>  		goto out;
>  	}
>  
> +	if (priv->regs_h)
> +		priv->intf_id = ioread32((u32 __iomem *)&priv->regs_h->intf_id);
> +
> +	if (priv->intf_id & CRB_INTF_CAP_CRB_CHUNK)
> +		dev_info(dev, "CRB Chunking is supported by backend\n");
> +
>  	memcpy_fromio(&__rsp_pa, &priv->regs_t->ctrl_rsp_pa, 8);
>  	rsp_pa = le64_to_cpu(__rsp_pa);
>  	rsp_size = ioread32(&priv->regs_t->ctrl_rsp_size);
> @@ -765,8 +894,10 @@ static int crb_map_io(struct device *dev, struct crb_priv *priv,
>  	priv->rsp = priv->cmd;
>  
>  out:
> -	if (!ret)
> +	if (!ret) {
>  		priv->cmd_size = cmd_size;
> +		priv->rsp_size = rsp_size;
> +	}
>  
>  	__crb_go_idle(dev, priv, 0);
>  
> -- 
> 2.54.0
> 

Looks pretty good. I'll hold r-by up until I've tested +1 revision of
the series (for which I provided rebased patch).

BR, Jarkko