linux-kernel - [PATCH V6 09/10] cxl/mem: Retry reading CDAT on failure

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Message-Id: <20220201071952.900068-10-ira.weiny@intel.com>
Date:   Mon, 31 Jan 2022 23:19:51 -0800
From:   ira.weiny@...el.com
To:     Dan Williams <dan.j.williams@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: [PATCH V6 09/10] cxl/mem: Retry reading CDAT on failure

From: Ira Weiny <ira.weiny@...el.com>

The CDAT read may fail for a number of reasons but mainly it is possible
to get different parts of a valid state.  The checksum in the CDAT table
protects against this.

Now that the checksum is validated issue a retry if the CDAT read fails.
For now 2 retries are implemented.

Signed-off-by: Ira Weiny <ira.weiny@...el.com>

---
NOTE: Is 2 enough?  Should this just be delayed until the time when the
data is actually needed and not there?

Changes from V5:
	New patch -- easy to push off or drop.
---
 drivers/cxl/core/memdev.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
index a01068e98333..11d721c56f08 100644
--- a/drivers/cxl/core/memdev.c
+++ b/drivers/cxl/core/memdev.c
@@ -356,7 +356,8 @@ static const struct file_operations cxl_memdev_fops = {
 	.llseek = noop_llseek,
 };
 
-static int read_cdat_data(struct cxl_memdev *cxlmd, struct cxl_dev_state *cxlds)
+static int __read_cdat_data(struct cxl_memdev *cxlmd,
+			    struct cxl_dev_state *cxlds)
 {
 	struct device *dev = &cxlmd->dev;
 	size_t cdat_length;
@@ -371,6 +372,20 @@ static int read_cdat_data(struct cxl_memdev *cxlmd, struct cxl_dev_state *cxlds)
 	return cxl_mem_cdat_read_table(cxlds, &cxlmd->cdat);
 }
 
+static int read_cdat_data(struct cxl_memdev *cxlmd,
+			  struct cxl_dev_state *cxlds)
+{
+	int retries = 2;
+	int rc;
+
+	while (--retries) {
+		rc = __read_cdat_data(cxlmd, cxlds);
+		if (!rc)
+			break;
+	}
+	return rc;
+}
+
 struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds)
 {
 	struct cxl_memdev *cxlmd;
-- 
2.31.1