If the platform doesn't support an event counter, enabling it using the
'counter_enable' debugfs attribute currently will succeed. But reading the
debugfs attribute back will return 'Counter Disabled'.

This could cause confusion to the users. So while enabling an event
counter in counter_enable_write(), always read back the status to check if
the counter is enabled or not. If not, return -EOPNOTSUPP to let the users
know that the event counter is not supported.

Fixes: 9f99c304c467 ("PCI: dwc: Add debugfs based Statistical Counter support for DWC")
Suggested-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
---
 .../pci/controller/dwc/pcie-designware-debugfs.c  | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-designware-debugfs.c b/drivers/pci/controller/dwc/pcie-designware-debugfs.c
index 9ff4d45e80f1..1f1bd9888327 100644
--- a/drivers/pci/controller/dwc/pcie-designware-debugfs.c
+++ b/drivers/pci/controller/dwc/pcie-designware-debugfs.c
@@ -352,6 +352,21 @@ static ssize_t counter_enable_write(struct file *file, const char __user *buf,
 		val |= FIELD_PREP(EVENT_COUNTER_ENABLE, PER_EVENT_OFF);
 
 	dw_pcie_writel_dbi(pci, rinfo->ras_cap_offset + RAS_DES_EVENT_COUNTER_CTRL_REG, val);
+
+	/*
+	 * While enabling the counter, always read back the status to check if
+	 * it is enabled or not. Return error if it is not enabled to let the
+	 * users know that the counter is not supported on the platform.
+	 */
+	if (enable) {
+		val = dw_pcie_readl_dbi(pci, rinfo->ras_cap_offset +
+					RAS_DES_EVENT_COUNTER_CTRL_REG);
+		if (!FIELD_GET(EVENT_COUNTER_STATUS, val)) {
+			mutex_unlock(&rinfo->reg_event_lock);
+			return -EOPNOTSUPP;
+		}
+	}
+
 	mutex_unlock(&rinfo->reg_event_lock);
 
 	return count;
-- 
2.25.1

Hello,

> If the platform doesn't support an event counter, enabling it using the
> 'counter_enable' debugfs attribute currently will succeed. But reading the
> debugfs attribute back will return 'Counter Disabled'.
> 
> This could cause confusion to the users. So while enabling an event
> counter in counter_enable_write(), always read back the status to check if
> the counter is enabled or not. If not, return -EOPNOTSUPP to let the users
> know that the event counter is not supported.

Thank you for following up on this.  Appreciated.  With that...

Reviewed-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

Thank you!

	Krzysztof