Re: [PATCH v7 5/5] Add debugfs based statistical counter support in DWC

On Tue, Mar 04, 2025 at 10:40:43PM +0530, Shradha Todi wrote:

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-----Original Message-----
From: Fan Ni <redacted>
Sent: 04 March 2025 02:33
To: Krzysztof Wilczyński <redacted>
Cc: Fan Ni <redacted>; Shradha Todi <redacted>; linux-kernel@vger.kernel.org; linux-
pci@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-perf-users@vger.kernel.org; manivannan.sadhasivam@linaro.org;
lpieralisi@kernel.org; robh@kernel.org; bhelgaas@google.com; jingoohan1@gmail.com; Jonathan.Cameron@huawei.com;
a.manzanares@samsung.com; pankaj.dubey@samsung.com; cassel@kernel.org; 18255117159@163.com;
xueshuai@linux.alibaba.com; renyu.zj@linux.alibaba.com; will@kernel.org; mark.rutland@arm.com
Subject: Re: [PATCH v7 5/5] Add debugfs based statistical counter support in DWC

On Tue, Mar 04, 2025 at 04:42:28AM +0900, Krzysztof Wilczyński wrote:

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Hello,

[...]

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+static ssize_t counter_value_read(struct file *file, char __user
+*buf, size_t count, loff_t *ppos) {
+	struct dwc_pcie_rasdes_priv *pdata = file->private_data;
+	struct dw_pcie *pci = pdata->pci;
+	struct dwc_pcie_rasdes_info *rinfo = pci->debugfs->rasdes_info;
+	char debugfs_buf[DWC_DEBUGFS_BUF_MAX];
+	ssize_t pos;
+	u32 val;
+
+	mutex_lock(&rinfo->reg_event_lock);
+	set_event_number(pdata, pci, rinfo);
+	val = dw_pcie_readl_dbi(pci, rinfo->ras_cap_offset + RAS_DES_EVENT_COUNTER_DATA_REG);
+	mutex_unlock(&rinfo->reg_event_lock);
+	pos = scnprintf(debugfs_buf, DWC_DEBUGFS_BUF_MAX, "Counter
+value: %d\n", val);
+
+	return simple_read_from_buffer(buf, count, ppos, debugfs_buf,
+pos); }

Do we need to check whether the counter is enabled or not for the
event before retrieving the counter value?

I believe, we have a patch that aims to address, have a look at:


https://lore.kernel.org/linux-pci/20250225171239.19574-1-manivannan.sa
dhasivam@linaro.org

Maybe I missed something, that seems to fix counter_enable_read(), but here is to retrieve counter value.
How dw_pcie_readl_dbi() can return something like "Counter Disabled"?

Fan

Hey Fan,
So the counter value will show 0 in case it is disabled so there will not be any issues as per say. We could add the
check here but I feel I have already exposed the functionality to check if a counter is enabled or disabled, (by reading the
counter_enable debugfs entry) so this could be handled in user space to only read the counter if it's enabled.

Ok. 
Returning 0 when the counter is disabled makes sense to me.

Just some thought.

It seems natural to me if we make "counter_value" only visiable to
users when the counter is enabled. 

Fan

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Thank you!

	Krzysztof