linux-kernel - [PATCH V10 8/9] cxl/port: Retry reading CDAT on failure

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Date:   Sat,  4 Jun 2022 17:50:48 -0700
From:   ira.weiny@...el.com
To:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     Ira Weiny <ira.weiny@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ben Widawsky <ben@...dawsk.net>, linux-kernel@...r.kernel.org,
        linux-cxl@...r.kernel.org, linux-pci@...r.kernel.org
Subject: [PATCH V10 8/9] cxl/port: 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 cdat data is validated issue a retries if the CDAT read
fails.  For now 5 retries are implemented.

Cc: Alison Schofield <alison.schofield@...el.com>
Cc: Davidlohr Bueso <dave@...olabs.net>
Signed-off-by: Ira Weiny <ira.weiny@...el.com>

---
Changes from V9
	Alison Schofield/Davidlohr Bueso
		Print debug on each iteration and error only after failure

Changes from V8
	Move code to cxl/core/pci.c

Changes from V6
	Move to pci.c
	Fix retries count
	Change to 5 retries

Changes from V5:
	New patch -- easy to push off or drop.
---
 drivers/cxl/core/pci.c | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
index 73e28b82ffcf..e68f13e66fcf 100644
--- a/drivers/cxl/core/pci.c
+++ b/drivers/cxl/core/pci.c
@@ -631,20 +631,18 @@ static int cxl_cdat_read_table(struct cxl_port *port,
 	return rc;
 }
 
-void read_cdat_data(struct cxl_port *port)
+static int __read_cdat_data(struct cxl_port *port)
 {
 	struct device *dev = &port->dev;
 	size_t cdat_length;
 	int ret;
 
 	if (cxl_cdat_get_length(port, &cdat_length))
-		return;
+		return 0;
 
 	port->cdat.table = devm_kzalloc(dev, cdat_length, GFP_KERNEL);
-	if (!port->cdat.table) {
-		ret = -ENOMEM;
-		goto error;
-	}
+	if (!port->cdat.table)
+		return -ENOMEM;
 
 	port->cdat.length = cdat_length;
 	ret = cxl_cdat_read_table(port, &port->cdat);
@@ -652,12 +650,26 @@ void read_cdat_data(struct cxl_port *port)
 		devm_kfree(dev, port->cdat.table);
 		port->cdat.table = NULL;
 		port->cdat.length = 0;
-		ret = -EIO;
-		goto error;
+		return -EIO;
 	}
 
-	return;
-error:
-	dev_err(dev, "CDAT data read error (%d)\n", ret);
+	return 0;
+}
+
+void read_cdat_data(struct cxl_port *port)
+{
+	int retries = 5;
+	int rc;
+
+	while (retries--) {
+		rc = __read_cdat_data(port);
+		if (!rc)
+			return;
+		dev_dbg(&port->dev,
+			"CDAT data read error rc=%d (retries %d)\n",
+			rc, retries);
+	}
+	dev_err(&port->dev, "CDAT data read failed after %d retries\n",
+		retries);
 }
 EXPORT_SYMBOL_NS_GPL(read_cdat_data, CXL);
-- 
2.35.1