[PATCH v3 1/5] powerpc/rtas: Handle ibm,open-errinjct return format

[Narayana Murty N <nnmlinux@linux.ibm.com>]

PAPR specifies that ibm,open-errinjct has a unique return-cell layout:

  rets[0] = injection session token (output parameter)
  rets[1] = status code

This differs from every other RTAS call, where:

  rets[0] = status code
  rets[1..] = output parameters

As a result, the existing rtas_call() convention — return value is the
RTAS status, outputs[] receives the non-status output values — must be
preserved while correctly extracting status from rets[1] for this one
call.

Add rtas_token_is_open_errinjct() and rtas_status_from_args() helpers.
rtas_status_from_args() selects the correct status cell based on the
token, and the output-copy loop in rtas_call() is updated so that for
ibm,open-errinjct:

  rtas_call() return = rets[1]   (RTAS status)
  outputs[0]        = rets[0]   (session token)

For all other calls the behaviour is unchanged: return value is rets[0]
and outputs[] receives rets[1..nret-1].

The sys_rtas userspace path is not modified: copy_to_user() still
copies raw RTAS return cells (rets[0..nret-1]) to userspace.

Callers passing a single output int (nret == 2) are safe because we
write at most nret-1 values into outputs[], never all nret cells.

Also move the '/* A -1 return code...*/' comment to immediately precede
the if (ret == -1) check it describes, and remove the redundant stale
else branch that re-assigned ret.

Reference: OpenPOWER PAPR documentation
           https://files.openpower.foundation/s/XFgfMaqLMD5Bcm8

Signed-off-by: Narayana Murty N <nnmlinux@linux.ibm.com>
---
 arch/powerpc/kernel/rtas.c | 51 ++++++++++++++++++++++++++++++++------
 1 file changed, 44 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 8d81c1e7a8db..27d53f34494d 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -1117,6 +1117,29 @@ static bool token_is_restricted_errinjct(s32 token)
 	       token == rtas_function_token(RTAS_FN_IBM_ERRINJCT);
 }
 
+/**
+ * rtas_token_is_open_errinjct() - Test whether @token identifies ibm,open-errinjct.
+ */
+static bool rtas_token_is_open_errinjct(int token)
+{
+	return token == rtas_function_token(RTAS_FN_IBM_OPEN_ERRINJCT);
+}
+
+/**
+ * rtas_status_from_args() - Extract the RTAS status code from a completed
+ *                           call's return-cell array.
+ *
+ * For ibm,open-errinjct the status lives in rets[1]; for every other
+ * RTAS function it lives in rets[0].
+ */
+static int rtas_status_from_args(int token, struct rtas_args *args, int nret)
+{
+	if (rtas_token_is_open_errinjct(token) && nret > 1)
+		return be32_to_cpu(args->rets[1]);
+
+	return nret > 0 ? be32_to_cpu(args->rets[0]) : 0;
+}
+
 /**
  * rtas_call() - Invoke an RTAS firmware function.
  * @token: Identifies the function being invoked.
@@ -1213,15 +1236,29 @@ int rtas_call(int token, int nargs, int nret, int *outputs, ...)
 	va_rtas_call_unlocked(args, token, nargs, nret, list);
 	va_end(list);
 
-	/* A -1 return code indicates that the last command couldn't
-	   be completed due to a hardware error. */
-	if (be32_to_cpu(args->rets[0]) == -1)
+	ret = rtas_status_from_args(token, args, nret);
+
+	/*
+	 * A -1 return code indicates that the last command couldn't
+	 * be completed due to a hardware error.
+	 */
+	if (ret == -1)
 		buff_copy = __fetch_rtas_last_error(NULL);
 
-	if (nret > 1 && outputs != NULL)
-		for (i = 0; i < nret-1; ++i)
-			outputs[i] = be32_to_cpu(args->rets[i + 1]);
-	ret = (nret > 0) ? be32_to_cpu(args->rets[0]) : 0;
+	if (nret > 1 && outputs != NULL) {
+		if (rtas_token_is_open_errinjct(token)) {
+			/*
+			 * ibm,open-errinjct: rets[0]=session token, rets[1]=status.
+			 * Expose session token in outputs[0]; skip rets[1] (status).
+			 */
+			outputs[0] = be32_to_cpu(args->rets[0]);
+			for (i = 1; i < nret - 1; ++i)
+				outputs[i] = be32_to_cpu(args->rets[i + 1]);
+		} else {
+			for (i = 0; i < nret - 1; ++i)
+				outputs[i] = be32_to_cpu(args->rets[i + 1]);
+		}
+	}
 
 	lockdep_unpin_lock(&rtas_lock, cookie);
 	raw_spin_unlock_irqrestore(&rtas_lock, flags);
-- 
2.54.0