[PATCH v4 3/3] powerpc/papr_scm: Force a scm-unbind if initial scm-bind fails

[Vaibhav Jain <vaibhav@linux.ibm.com>]

In some cases initial bind of scm memory for an lpar can fail if
previously it wasn't released using a scm-unbind hcall. This situation
can arise due to panic of the previous kernel or forced lpar
fadump. In such cases the H_SCM_BIND_MEM return a H_OVERLAP error.

To mitigate such cases the patch updates papr_scm_probe() to force a
call to drc_pmem_unbind() in case the initial bind of scm memory fails
with EBUSY error. In case scm-bind operation again fails after the
forced scm-unbind then we follow the existing error path. We also
update drc_pmem_bind() to handle the H_OVERLAP error returned by phyp
and indicate it as a EBUSY error back to the caller.

Suggested-by: "Oliver O'Halloran" <oohall@gmail.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Reviewed-by: Oliver O'Halloran <oohall@gmail.com>
---
Change-log:

v4:
* None. Re-spinning the patchset.

v3:
* Minor update to a code comment. [Oliver]

v2:
* Moved the retry code from drc_pmem_bind() to papr_scm_probe()
  [Oliver]
* Changed the type of variable 'rc' in drc_pmem_bind() to
  int64_t. [Oliver]
---
 arch/powerpc/platforms/pseries/papr_scm.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
index c01a03fd3ee7..7c5e10c063a0 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c
@@ -43,8 +43,9 @@ struct papr_scm_priv {
 static int drc_pmem_bind(struct papr_scm_priv *p)
 {
 	unsigned long ret[PLPAR_HCALL_BUFSIZE];
-	uint64_t rc, token;
 	uint64_t saved = 0;
+	uint64_t token;
+	int64_t rc;
 
 	/*
 	 * When the hypervisor cannot map all the requested memory in a single
@@ -64,6 +65,10 @@ static int drc_pmem_bind(struct papr_scm_priv *p)
 	} while (rc == H_BUSY);
 
 	if (rc) {
+		/* H_OVERLAP needs a separate error path */
+		if (rc == H_OVERLAP)
+			return -EBUSY;
+
 		dev_err(&p->pdev->dev, "bind err: %lld\n", rc);
 		return -ENXIO;
 	}
@@ -331,6 +336,14 @@ static int papr_scm_probe(struct platform_device *pdev)
 
 	/* request the hypervisor to bind this region to somewhere in memory */
 	rc = drc_pmem_bind(p);
+
+	/* If phyp says drc memory still bound then force unbound and retry */
+	if (rc == -EBUSY) {
+		dev_warn(&pdev->dev, "Retrying bind after unbinding\n");
+		drc_pmem_unbind(p);
+		rc = drc_pmem_bind(p);
+	}
+
 	if (rc)
 		goto err;
 
-- 
2.21.0