[PATCH] hwrng: xilinx-trng: propagate timeout before any data is read

[Pengpeng Hou]

xtrng_readblock32() polls for 16-byte chunks but returns the number of
bytes read even when the first poll times out. Its caller then treats a
zero return as a short successful read, and partial reads for full
32-byte blocks can make the tail copy use a fixed block offset rather
than the amount already produced.

Return the poll error when no data has been read, preserve partial
positive returns after some data is available, stop the generator on all
collection exits, and append tail bytes at the current output count.

Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
---
 drivers/char/hw_random/xilinx-trng.c | 32 +++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 8 deletions(-)

diff --git a/drivers/char/hw_random/xilinx-trng.c b/drivers/char/hw_random/xilinx-trng.c
index f615d5adddde..4a1a168bb46a 100644
--- a/drivers/char/hw_random/xilinx-trng.c
+++ b/drivers/char/hw_random/xilinx-trng.c
@@ -87,8 +87,8 @@ static void xtrng_softreset(struct xilinx_rng *rng)
 	xtrng_readwrite32(rng->rng_base + TRNG_CTRL_OFFSET, TRNG_CTRL_PRNGSRST_MASK, 0);
 }
 
-/* Return no. of bytes read */
-static size_t xtrng_readblock32(void __iomem *rng_base, __be32 *buf, int blocks32, bool wait)
+/* Return no. of bytes read or a negative error before any data is read. */
+static int xtrng_readblock32(void __iomem *rng_base, __be32 *buf, int blocks32, bool wait)
 {
 	int read = 0, ret;
 	int timeout = 1;
@@ -103,8 +103,11 @@ static size_t xtrng_readblock32(void __iomem *rng_base, __be32 *buf, int blocks3
 		ret = readl_poll_timeout(rng_base + TRNG_STATUS_OFFSET, val,
 					 (val & TRNG_STATUS_QCNT_MASK) ==
 					 TRNG_STATUS_QCNT_16_BYTES, !!wait, timeout);
-		if (ret)
+		if (ret) {
+			if (!read)
+				return ret;
 			break;
+		}
 
 		for (idx = 0; idx < TRNG_READ_4_WORD; idx++) {
 			*(buf + read) = cpu_to_be32(ioread32(rng_base + TRNG_CORE_OUTPUT_OFFSET));
@@ -119,27 +122,40 @@ static int xtrng_collect_random_data(struct xilinx_rng *rng, u8 *rand_gen_buf,
 {
 	u8 randbuf[TRNG_SEC_STRENGTH_BYTES];
 	int byteleft, blocks, count = 0;
+	int full_blocks_bytes;
 	int ret;
 
 	byteleft = no_of_random_bytes & (TRNG_SEC_STRENGTH_BYTES - 1);
 	blocks = no_of_random_bytes >> TRNG_SEC_STRENGTH_SHIFT;
+	full_blocks_bytes = blocks * TRNG_SEC_STRENGTH_BYTES;
 	xtrng_readwrite32(rng->rng_base + TRNG_CTRL_OFFSET, TRNG_CTRL_PRNGSTART_MASK,
 			  TRNG_CTRL_PRNGSTART_MASK);
 	if (blocks) {
 		ret = xtrng_readblock32(rng->rng_base, (__be32 *)rand_gen_buf, blocks, wait);
-		if (!ret)
-			return 0;
+		if (ret <= 0) {
+			count = ret;
+			goto out_stop;
+		}
 		count += ret;
+		if (ret < full_blocks_bytes)
+			goto out_stop;
 	}
 
 	if (byteleft) {
 		ret = xtrng_readblock32(rng->rng_base, (__be32 *)randbuf, 1, wait);
+		if (ret < 0) {
+			if (!count)
+				count = ret;
+			goto out_stop;
+		}
 		if (!ret)
-			return count;
-		memcpy(rand_gen_buf + (blocks * TRNG_SEC_STRENGTH_BYTES), randbuf, byteleft);
-		count += byteleft;
+			goto out_stop;
+		ret = min(ret, no_of_random_bytes - count);
+		memcpy(rand_gen_buf + count, randbuf, ret);
+		count += ret;
 	}
 
+out_stop:
 	xtrng_readwrite32(rng->rng_base + TRNG_CTRL_OFFSET,
 			  TRNG_CTRL_PRNGMODE_MASK | TRNG_CTRL_PRNGSTART_MASK, 0U);
 
-- 
2.50.1 (Apple Git-155)