[PATCH 4/4] memory: brcmstb_dpfe: introduce best-effort API detection

[Markus Mayer <mmayer@broadcom.com>]

Add a best-effort probe function that tries all known DPFE versions to
see if one might actually work. This helps in cases where device tree
doesn't provide the proper version information for whatever reason. In
that case, the driver may still be able to register if one of the known
API versions ends up working.

Caveat: we have to skip "v1" during our best effort attempts. This is
due to the fact that attempting a firmware download as required by v1
will result in a memory access violation on anything but v1 hardware.
This would crash the kernel. Since we don't know the HW version, we need
to play it safe and skip v1.

Signed-off-by: Markus Mayer <mmayer@broadcom.com>
---
 drivers/memory/brcmstb_dpfe.c | 58 ++++++++++++++++++++++++++++++++++-
 1 file changed, 57 insertions(+), 1 deletion(-)

diff --git a/drivers/memory/brcmstb_dpfe.c b/drivers/memory/brcmstb_dpfe.c
index 0b0a9b85b605..15f4ee3b8535 100644
--- a/drivers/memory/brcmstb_dpfe.c
+++ b/drivers/memory/brcmstb_dpfe.c
@@ -879,6 +879,50 @@ static int brcmstb_dpfe_resume(struct platform_device *pdev)
 	return brcmstb_dpfe_download_firmware(priv);
 }
 
+static int brcmstb_dpfe_probe_best_effort(struct platform_device *pdev)
+{
+	const char versioned_compat[] = "brcm,dpfe-cpu-v";
+	const char v1_str[] = "-v1";
+	const struct of_device_id *matches;
+	const struct dpfe_api *orig_dpfe_api;
+	struct device *dev = &pdev->dev;
+	struct brcmstb_dpfe_priv *priv;
+	int ret = -ENODEV;
+
+	priv = dev_get_drvdata(dev);
+	orig_dpfe_api = priv->dpfe_api;
+	matches = dev->driver->of_match_table;
+
+	/* Loop over all compatible strings */
+	for (; matches->compatible[0]; matches++) {
+		const char *compat = matches->compatible;
+		/* Find the ones that start with "brcm,dpfe-cpu-v" */
+		if (strstr(compat, versioned_compat) == compat) {
+			char *v1_ptr = strstr(compat, v1_str);
+			/*
+			 * We must skip v1, since we don't know the hardware
+			 * version and attempting a firmware download on v2 and
+			 * newer would crash the kernel due to a memory access
+			 * violation.
+			 * We make sure to match "-v1" at the end of the string
+			 * only.
+			 */
+			if (v1_ptr && v1_ptr[sizeof(v1_str)] == '\0')
+				continue;
+			priv->dpfe_api = matches->data;
+			/* Fingers crossed... */
+			ret = brcmstb_dpfe_download_firmware(priv);
+			if (!ret)
+				return 0;
+		}
+	}
+
+	/* It didn't work, so let's clean up. */
+	priv->dpfe_api = orig_dpfe_api;
+
+	return ret;
+}
+
 static int brcmstb_dpfe_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -923,8 +967,20 @@ static int brcmstb_dpfe_probe(struct platform_device *pdev)
 	}
 
 	ret = brcmstb_dpfe_download_firmware(priv);
+	if (ret && ret != -EPROBE_DEFER) {
+		/*
+		 * If the information provided by Device Tree didn't work, let's
+		 * try all known version. Maybe one will work.
+		 */
+		dev_warn(dev,
+			"DPFE v%d didn't work, reverting to best-effort\n",
+			priv->dpfe_api->version);
+		dev_warn(dev,
+			"Device Tree and / or the driver should be updated\n");
+		ret = brcmstb_dpfe_probe_best_effort(pdev);
+	}
 	if (ret)
-		return dev_err_probe(dev, ret, "Couldn't download firmware\n");
+		return dev_err_probe(dev, ret, "Unable to talk to DCPU\n");
 
 	ret = sysfs_create_groups(&pdev->dev.kobj, priv->dpfe_api->sysfs_attrs);
 	if (!ret)
-- 
2.43.0


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