[PATCH v4 1/2] cxl/region: Find free cxl decoder by device_for_each_child()

[Zijun Hu <zijun_hu@icloud.com>]

From: Zijun Hu <quic_zijuhu@quicinc.com>

To prepare for constifying the following old driver core API:

struct device *device_find_child(struct device *dev, void *data,
		int (*match)(struct device *dev, void *data));
to new:
struct device *device_find_child(struct device *dev, const void *data,
		int (*match)(struct device *dev, const void *data));

The new API does not allow its match function (*match)() to modify
caller's match data @*data, but match_free_decoder() as the old API's
match function indeed modifies relevant match data, so it is not suitable
for the new API any more, solved by using device_for_each_child() to
implement relevant finding free cxl decoder function.

By the way, this commit does not change any existing logic.

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
---
 drivers/cxl/core/region.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 21ad5f242875..c2068e90bf2f 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -794,10 +794,15 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos)
 	return rc;
 }
 
+struct cxld_match_data {
+	int id;
+	struct device *target_device;
+};
+
 static int match_free_decoder(struct device *dev, void *data)
 {
+	struct cxld_match_data *match_data = data;
 	struct cxl_decoder *cxld;
-	int *id = data;
 
 	if (!is_switch_decoder(dev))
 		return 0;
@@ -805,17 +810,31 @@ static int match_free_decoder(struct device *dev, void *data)
 	cxld = to_cxl_decoder(dev);
 
 	/* enforce ordered allocation */
-	if (cxld->id != *id)
+	if (cxld->id != match_data->id)
 		return 0;
 
-	if (!cxld->region)
+	if (!cxld->region) {
+		match_data->target_device = get_device(dev);
 		return 1;
+	}
 
-	(*id)++;
+	match_data->id++;
 
 	return 0;
 }
 
+/* NOTE: need to drop the reference with put_device() after use. */
+static struct device *find_free_decoder(struct device *parent)
+{
+	struct cxld_match_data match_data = {
+		.id = 0,
+		.target_device = NULL,
+	};
+
+	device_for_each_child(parent, &match_data, match_free_decoder);
+	return match_data.target_device;
+}
+
 static int match_auto_decoder(struct device *dev, void *data)
 {
 	struct cxl_region_params *p = data;
@@ -840,7 +859,6 @@ cxl_region_find_decoder(struct cxl_port *port,
 			struct cxl_region *cxlr)
 {
 	struct device *dev;
-	int id = 0;
 
 	if (port == cxled_to_port(cxled))
 		return &cxled->cxld;
@@ -849,7 +867,7 @@ cxl_region_find_decoder(struct cxl_port *port,
 		dev = device_find_child(&port->dev, &cxlr->params,
 					match_auto_decoder);
 	else
-		dev = device_find_child(&port->dev, &id, match_free_decoder);
+		dev = find_free_decoder(&port->dev);
 	if (!dev)
 		return NULL;
 	/*

-- 
2.34.1