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

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Message-ID: <Z8fSWcR_aXyxmFEZ@debian>
Date: Tue, 4 Mar 2025 20:26:01 -0800
From: Fan Ni <nifan.cxl@...il.com>
To: Shradha Todi <shradha.t@...sung.com>
Cc: 'Fan Ni' <nifan.cxl@...il.com>,
	'Krzysztof Wilczyński' <kw@...ux.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-perf-users@...r.kernel.org, manivannan.sadhasivam@...aro.org,
	lpieralisi@...nel.org, robh@...nel.org, bhelgaas@...gle.com,
	jingoohan1@...il.com, Jonathan.Cameron@...wei.com,
	a.manzanares@...sung.com, pankaj.dubey@...sung.com,
	cassel@...nel.org, 18255117159@....com, xueshuai@...ux.alibaba.com,
	renyu.zj@...ux.alibaba.com, will@...nel.org, mark.rutland@....com
Subject: 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:
> 
> 
> > -----Original Message-----
> > From: Fan Ni <nifan.cxl@...il.com>
> > Sent: 04 March 2025 02:33
> > To: Krzysztof Wilczyński <kw@...ux.com>
> > Cc: Fan Ni <nifan.cxl@...il.com>; Shradha Todi <shradha.t@...sung.com>; linux-kernel@...r.kernel.org; linux-
> > pci@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; linux-perf-users@...r.kernel.org; manivannan.sadhasivam@...aro.org;
> > lpieralisi@...nel.org; robh@...nel.org; bhelgaas@...gle.com; jingoohan1@...il.com; Jonathan.Cameron@...wei.com;
> > a.manzanares@...sung.com; pankaj.dubey@...sung.com; cassel@...nel.org; 18255117159@....com;
> > xueshuai@...ux.alibaba.com; renyu.zj@...ux.alibaba.com; will@...nel.org; mark.rutland@....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:
> > > Hello,
> > >
> > > [...]
> > > > > +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@...aro.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
> 
> > >
> > > Thank you!
> > >
> > > 	Krzysztof
> 
>