linux-kernel - Re: [PATCH v7 3/5] Add debugfs based silicon debug support in DWC

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Message-ID: <20250304171154.njoygsvfd567pb66@thinkpad>
Date: Tue, 4 Mar 2025 22:41:54 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Krzysztof Wilczyński <kw@...ux.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>, 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, 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,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v7 3/5] Add debugfs based silicon debug support in DWC

On Wed, Mar 05, 2025 at 12:46:38AM +0900, Krzysztof Wilczyński wrote:
> Hello,
> 
> > This patch is now commit 1ff54f4cbaed9ec6 ("PCI: dwc: Add debugfs
> > based Silicon Debug support for DWC") in pci/next (next-20250304).
> > 
> > On Mon, 3 Mar 2025 at 20:47, Krzysztof Wilczyński <kw@...ux.com> wrote:
> > > [...]
> > > > > +int dwc_pcie_debugfs_init(struct dw_pcie *pci)
> > > > > +{
> > > > > +   char dirname[DWC_DEBUGFS_BUF_MAX];
> > > > > +   struct device *dev = pci->dev;
> > > > > +   struct debugfs_info *debugfs;
> > > > > +   struct dentry *dir;
> > > > > +   int ret;
> > > > > +
> > > > > +   /* Create main directory for each platform driver */
> > > > > +   snprintf(dirname, DWC_DEBUGFS_BUF_MAX, "dwc_pcie_%s", dev_name(dev));
> > > > > +   dir = debugfs_create_dir(dirname, NULL);
> > > > > +   debugfs = devm_kzalloc(dev, sizeof(*debugfs), GFP_KERNEL);
> > > > > +   if (!debugfs)
> > > > > +           return -ENOMEM;
> > > > > +
> > > > > +   debugfs->debug_dir = dir;
> > > > > +   pci->debugfs = debugfs;
> > > > > +   ret = dwc_pcie_rasdes_debugfs_init(pci, dir);
> > > > > +   if (ret)
> > > > > +           dev_dbg(dev, "RASDES debugfs init failed\n");
> > > >
> > > > What will happen if ret != 0? still return 0?
> > 
> > And that is exactly what happens on Gray Hawk Single with R-Car
> > V4M: dw_pcie_find_rasdes_capability() returns NULL, causing
> > dwc_pcie_rasdes_debugfs_init() to return -ENODEV.
> 
> Thank you for testing and for catching this issue.  Much appreciated.
> 
> > > Given that callers of dwc_pcie_debugfs_init() check for errors,
> > 
> > Debugfs issues should never be propagated upstream!
> 
> Makes complete sense.  Sorry for breaking things here!
> 
> > > this probably should correctly bubble up any failure coming from
> > > dwc_pcie_rasdes_debugfs_init().
> > >
> > > I made updates to the code directly on the current branch, have a look:
> > 
> > So while applying, you changed this like:
> > 
> >             ret = dwc_pcie_rasdes_debugfs_init(pci, dir);
> >     -       if (ret)
> >     -               dev_dbg(dev, "RASDES debugfs init failed\n");
> >     +       if (ret) {
> >     +               dev_err(dev, "failed to initialize RAS DES debugfs\n");
> >     +               return ret;
> >     +       }
> > 
> >             return 0;
> > 
> > Hence this is now a fatal error, causing the probe to fail.
> 
> I removed the changed, and also move the log level to be a warning, per:
> 
>   https://web.git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/commit/?h=controller/dwc&id=c6759a967e69aba16aef0d92f43e527b112e98a5
> 
> Would this be acceptable here?
> 
> Mani, would this be acceptable to you, too?  Given that you posted the
> following recently:
> 
>   https://lore.kernel.org/linux-pci/20250303200055.GA1881771@rocinante/T/#mab9cbd5834390d259afea056eee9a73d8c3b435f
> 
> That said, perhaps moving the log level to a debug would be better served here.
> 

Even though debugfs_init() failure is not supposed to fail the probe(),
dwc_pcie_rasdes_debugfs_init() has a devm_kzalloc() and propagating that
failure would be canolically correct IMO.

So I would still opt to have my version + your previous one.

- Mani

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