[PATCH 1/1] rng: detect RISC-V Zkr RNG device in bind method

[Heinrich Schuchardt]

The existence of devices should be checked in the bind method and not in
the probe method. Adjust the RISC-V Zkr RNG driver accordingly.

Use ENOENT (and not ENODEV) to signal that the device is not available.

Fixes: ceec977ba1a9 ("rng: Provide a RNG based on the RISC-V Zkr ISA extension")
Reported-by: Andre Przywara <andre.przyw...@arm.com>
Signed-off-by: Heinrich Schuchardt <heinrich.schucha...@canonical.com>
---
 drivers/rng/riscv_zkr_rng.c | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/drivers/rng/riscv_zkr_rng.c b/drivers/rng/riscv_zkr_rng.c
index 8c9e111e2e..48a5251988 100644
--- a/drivers/rng/riscv_zkr_rng.c
+++ b/drivers/rng/riscv_zkr_rng.c
@@ -55,7 +55,7 @@ static int riscv_zkr_read(struct udevice *dev, void *data, 
size_t len)
                        }
                        break;
                case DEAD:
-                       return -ENODEV;
+                       return -ENOENT;
                }
        }
 
@@ -63,16 +63,16 @@ static int riscv_zkr_read(struct udevice *dev, void *data, 
size_t len)
 }
 
 /**
- * riscv_zkr_probe() - check if the seed register is available
+ * riscv_zkr_bind() - check if the seed register is available
  *
- * If the SBI software has not set mseccfg.sseed=1 or the Zkr
- * extension is not available this probe function will result
- * in an exception. Currently we cannot recover from this.
+ * If the SBI software has not set mseccfg.sseed=1 or the Zkr extension is not
+ * available, reading the seed register will result in an exception from which
+ * this function safely resumes.
  *
  * @dev:       RNG device
  * Return:     0 if successfully probed
  */
-static int riscv_zkr_probe(struct udevice *dev)
+static int riscv_zkr_bind(struct udevice *dev)
 {
        struct resume_data resume;
        int ret;
@@ -87,7 +87,24 @@ static int riscv_zkr_probe(struct udevice *dev)
                val = read_seed();
        set_resume(NULL);
        if (ret)
-               return -ENODEV;
+               return -ENOENT;
+
+       return 0;
+}
+
+/**
+ * riscv_zkr_probe() - check if entropy is available
+ *
+ * The bind method already checked that the seed register can be read without
+ * excpetiong. Here we wait for the self test to finish and entropy becoming
+ * available.
+ *
+ * @dev:       RNG device
+ * Return:     0 if successfully probed
+ */
+static int riscv_zkr_probe(struct udevice *dev)
+{
+       u32 val;
 
        do {
                val = read_seed();
@@ -95,7 +112,7 @@ static int riscv_zkr_probe(struct udevice *dev)
        } while (val == BIST || val == WAIT);
 
        if (val == DEAD)
-               return -ENODEV;
+               return -ENOENT;
 
        return 0;
 }
@@ -108,6 +125,7 @@ U_BOOT_DRIVER(riscv_zkr) = {
        .name = DRIVER_NAME,
        .id = UCLASS_RNG,
        .ops = &riscv_zkr_ops,
+       .bind = riscv_zkr_bind,
        .probe = riscv_zkr_probe,
 };
 
-- 
2.40.1