[PATCH v9 1/3] cxl/region: Simplify poison_by_decoder() error handling

[Richard Cheng <icheng@nvidia.com>]

"rc" carries both an error code and the loop control
signal for device_for_each_child(), so returning it bare is misleading,
the early guards mean "keep walking", not "no error". Zeroing "rc" to
forgive an -EFAULT on a RAM partition adds to that by discarding what
the device actually returned.

Return a literal 0 where the walk should continue, and test the
forgiven case directly instead of rewriting "rc". Give that test a
name, poison_efault_forgiven(), so cxl_get_poison_unmapped() and
poison_by_decoder() spell the same rule the same way. No functional
change.

Suggested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Richard Cheng <icheng@nvidia.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
---
Changelog:

v8 -> v9:
    - Add the poison_efault_forgiven() helper and use it in
      cxl_get_poison_unmapped()

v7 -> v8:
    - New patch. Splits the poison_by_decoder() readability cleanup out
      of "cxl/hdm: Allow zero sized HDM decoders" so the functional
      change is not mixed with a refactor of pre-existing code.
---
 drivers/cxl/core/region.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 1e211542b6b6..45536909cc17 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -2905,6 +2905,16 @@ struct cxl_poison_context {
 	u64 offset;
 };
 
+/*
+ * A device may answer a Get Poison List request with "physical address
+ * specified is invalid" (-EFAULT). That answer is tolerated for a RAM
+ * partition and the poison walk continues.
+ */
+static inline bool poison_efault_forgiven(int rc, enum cxl_partition_mode mode)
+{
+	return rc == -EFAULT && mode == CXL_PARTMODE_RAM;
+}
+
 static int cxl_get_poison_unmapped(struct cxl_memdev *cxlmd,
 				   struct cxl_poison_context *ctx)
 {
@@ -2933,7 +2943,7 @@ static int cxl_get_poison_unmapped(struct cxl_memdev *cxlmd,
 		if (!length)
 			break;
 		rc = cxl_mem_get_poison(cxlmd, offset, length, NULL);
-		if (rc == -EFAULT && cxlds->part[i].mode == CXL_PARTMODE_RAM)
+		if (poison_efault_forgiven(rc, cxlds->part[i].mode))
 			continue;
 		if (rc)
 			break;
@@ -2950,14 +2960,14 @@ static int poison_by_decoder(struct device *dev, void *arg)
 	struct cxl_dev_state *cxlds;
 	struct cxl_memdev *cxlmd;
 	u64 offset, length;
-	int rc = 0;
+	int rc;
 
 	if (!is_endpoint_decoder(dev))
-		return rc;
+		return 0;
 
 	cxled = to_cxl_endpoint_decoder(dev);
 	if (!cxled->dpa_res)
-		return rc;
+		return 0;
 
 	cxlmd = cxled_to_memdev(cxled);
 	cxlds = cxlmd->cxlds;
@@ -2967,18 +2977,14 @@ static int poison_by_decoder(struct device *dev, void *arg)
 		offset = cxled->dpa_res->start - cxled->skip;
 		length = cxled->skip;
 		rc = cxl_mem_get_poison(cxlmd, offset, length, NULL);
-		if (rc == -EFAULT && mode == CXL_PARTMODE_RAM)
-			rc = 0;
-		if (rc)
+		if (rc && !poison_efault_forgiven(rc, mode))
 			return rc;
 	}
 
 	offset = cxled->dpa_res->start;
 	length = cxled->dpa_res->end - offset + 1;
 	rc = cxl_mem_get_poison(cxlmd, offset, length, cxled->cxld.region);
-	if (rc == -EFAULT && mode == CXL_PARTMODE_RAM)
-		rc = 0;
-	if (rc)
+	if (rc && !poison_efault_forgiven(rc, mode))
 		return rc;
 
 	/* Iterate until commit_end is reached */
-- 
2.43.0