Re: [RFC PATCH 15/20] cxl: Add a routine to find cxl root decoder on cxl bus

[Neeraj Kumar]

On 26/06/25 12:19PM, Alison Schofield wrote:

On Tue, Jun 17, 2025 at 06:09:39PM +0530, Neeraj Kumar wrote:

Add cxl_find_root_decoder to find root decoder on cxl bus. It is used to
find root decoder during region creation

Does the existing to_cxl_root_decoder() provide what you need here?

Hi Alison,

Actually, my need is to find decoder0.0 from port1, with which endpoint device 
is connected.
Here i am already using to_cxl_root_decoder() inside cxl_find_root_decoder().
In cxl_find_root_decoder(), First i am finding dev which is required by 
to_cxl_root_decoder()

        struct cxl_root_decoder *cxl_find_root_decoder(struct cxl_port *port)
        {
                struct cxl_root *cxl_root __free(put_cxl_root) = 
find_cxl_root(port);
                struct device *dev = device_find_child(&cxl_root->port.dev, 
NULL, match_root_decoder);
                return to_cxl_root_decoder(dev);
        }


Thanks,
Neeraj

Signed-off-by: Neeraj Kumar <s.nee...@samsung.com>
---
 drivers/cxl/core/port.c | 26 ++++++++++++++++++++++++++
 drivers/cxl/cxl.h       |  1 +
 2 files changed, 27 insertions(+)

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index 2452f7c15b2d..94d9322b8e38 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -513,6 +513,32 @@ struct cxl_switch_decoder *to_cxl_switch_decoder(struct 
device *dev)
 }
 EXPORT_SYMBOL_NS_GPL(to_cxl_switch_decoder, "CXL");

+static int match_root_decoder(struct device *dev, void *data)
+{
+       return is_root_decoder(dev);
+}
+
+/**
+ * cxl_find_root_decoder() - find a cxl root decoder on cxl bus
+ * @port: any descendant port in root-cxl-port topology
+ */
+struct cxl_root_decoder *cxl_find_root_decoder(struct cxl_port *port)
+{
+       struct cxl_root *cxl_root __free(put_cxl_root) = find_cxl_root(port);
+       struct device *dev;
+
+       if (!cxl_root)
+               return NULL;
+
+       dev = device_find_child(&cxl_root->port.dev, NULL, match_root_decoder);
+
+       if (!dev)
+               return NULL;
+
+       return to_cxl_root_decoder(dev);
+}
+EXPORT_SYMBOL_NS_GPL(cxl_find_root_decoder, "CXL");
+
 static void cxl_ep_release(struct cxl_ep *ep)
 {
        put_device(ep->ep);
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 30c80e04cb27..2c6a782d0941 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -871,6 +871,7 @@ bool is_cxl_nvdimm_bridge(struct device *dev);
 int devm_cxl_add_nvdimm(struct cxl_port *parent_port, struct cxl_memdev 
*cxlmd);
 struct cxl_nvdimm_bridge *cxl_find_nvdimm_bridge(struct cxl_port *port);
 void cxl_region_discovery(struct cxl_port *port);
+struct cxl_root_decoder *cxl_find_root_decoder(struct cxl_port *port);

 #ifdef CONFIG_CXL_REGION
 bool is_cxl_pmem_region(struct device *dev);
--
2.34.1