[RFC v2 5/5] tpm: tis_i2c: Use local 4KB buffer to limit memory usage

[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 6cd07dd34507e..db19d459ea1e1 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;
 
-- 
2.53.0