Re: [PATCH] soc: qcom: llcc: Add llcc device availability check

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On 2/26/2024 4:19 PM, Sahil Chandna wrote:
On 2/26/2024 4:02 PM, Mukesh Ojha wrote:

On 2/22/2024 11:37 PM, Sahil Chandna wrote:
On 2/20/2024 5:58 PM, Mukesh Ojha wrote:
When llcc driver is enabled  and llcc device is not
physically there on the SoC, client can get
-EPROBE_DEFER on calling llcc_slice_getd() and it
is possible they defer forever.

Let's add a check device availabilty and set the
appropriate applicable error in drv_data.

Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
  drivers/soc/qcom/llcc-qcom.c | 23 ++++++++++++++++++++++-
  1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/soc/qcom/llcc-qcom.c b/drivers/soc/qcom/llcc-qcom.c
index 4ca88eaebf06..cb336b183bba 100644
--- a/drivers/soc/qcom/llcc-qcom.c
+++ b/drivers/soc/qcom/llcc-qcom.c
@@ -769,6 +769,27 @@ static const struct qcom_sct_config x1e80100_cfgs = {
  static struct llcc_drv_data *drv_data = (void *) -EPROBE_DEFER;
+static DEFINE_MUTEX(dev_avail);
what is the requirement for mutex lock here? Since we are only trying to find if node present or not

I was trying to avoid two parallel call from llcc_slice_getd() calling
parallel call to of_find_node_by_name() as it should be one time search for device presence to find a node and check if device is present or


Got it, but of_find_node_by_name () is holding a raw_spin_lock_irqsave () for concurrency, right ? please correct me if understanding is wrong.

Even though, of_find_node_by_name () is holding spin_lock but nothing
is preventing the 2nd call from happening. Here, mutex and check on
!ptr ensures, we don't make 2nd call.

+static bool is_llcc_device_available(void)
+    static struct llcc_drv_data *ptr;
+    mutex_lock(&dev_avail);
+    if (!ptr) {
+        struct device_node *node;
+        node = of_find_node_by_name(NULL, "system-cache-controller");
+        if (!of_device_is_available(node)) {
+            pr_warn("llcc-qcom: system-cache-controller node not found\n");
+            drv_data = ERR_PTR(-ENODEV);
+        }
+        of_node_put(node);
+        ptr = drv_data;
+    }
+    mutex_unlock(&dev_avail);
+    return (PTR_ERR(ptr) != -ENODEV) ? true : false;
   * llcc_slice_getd - get llcc slice descriptor
@@ -783,7 +804,7 @@ struct llcc_slice_desc *llcc_slice_getd(u32 uid)
      struct llcc_slice_desc *desc;
      u32 sz, count;
-    if (IS_ERR(drv_data))
+    if (!is_llcc_device_available() || IS_ERR(drv_data))
Also, thinking about this, should the status of device present or not be saved in static variable instead of function call for each client ?
          return ERR_CAST(drv_data);
      cfg = drv_data->cfg;


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