[PATCH 1/2] PCI: dwc: Add LTSSM tracing support to debugfs

[Manivannan Sadhasivam]

On Thu, Jan 08, 2026 at 09:01:43AM +0800, Shawn Lin wrote:
> 在 2026/01/07 星期三 20:41, Manivannan Sadhasivam 写道:
> > On Tue, Jan 06, 2026 at 05:18:38PM +0800, Shawn Lin wrote:
> > > Some platforms may provide LTSSM trace functionality, recording historical
> > > LTSSM state transition information. This is very useful for debugging, such
> > > as when certain devices cannot be recognized. Add an ltssm_trace operation
> > > node in debugfs for platform which could provide these information to show
> > > the LTSSM history.
> > > 
> > 
> > Why don't you implement it as a tracepoint since you want to expose traces?
> > 
> 
> I evaluated this option but didn't choose to do it just as I didn't
> want to select CONFIG_TRACING_SUPPORT for dwc driver because of this
> cheap function. But I'm fine to implement it as a tracepoint. Just to
> make it clear, if a tracepoint is preferred, should I need to create a new
> file like pcie-designware-trace?
> 

I would prefer that, because that will allow us to add more tracepoints in the
future and not muddle pcie-designware.h. General convention is to define
trace events in a separate header.

- Mani

> > - Mani
> > 
> > > Signed-off-by: Shawn Lin <shawn.lin at rock-chips.com>
> > > ---
> > >   .../controller/dwc/pcie-designware-debugfs.c  | 44 +++++++++++++++++++
> > >   drivers/pci/controller/dwc/pcie-designware.h  |  6 +++
> > >   2 files changed, 50 insertions(+)
> > > 
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware-debugfs.c b/drivers/pci/controller/dwc/pcie-designware-debugfs.c
> > > index df98fee69892..569e8e078ef2 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware-debugfs.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware-debugfs.c
> > > @@ -511,6 +511,38 @@ static int ltssm_status_open(struct inode *inode, struct file *file)
> > >   	return single_open(file, ltssm_status_show, inode->i_private);
> > >   }
> > > +static struct dw_pcie_ltssm_history *dw_pcie_ltssm_trace(struct dw_pcie *pci)
> > > +{
> > > +	if (pci->ops && pci->ops->ltssm_trace)
> > > +		return pci->ops->ltssm_trace(pci);
> > > +
> > > +	return NULL;
> > > +}
> > > +
> > > +static int ltssm_trace_show(struct seq_file *s, void *v)
> > > +{
> > > +	struct dw_pcie *pci = s->private;
> > > +	struct dw_pcie_ltssm_history *history;
> > > +	enum dw_pcie_ltssm val;
> > > +	u32 loop;
> > > +
> > > +	history = dw_pcie_ltssm_trace(pci);
> > > +	if (!history)
> > > +		return 0;
> > > +
> > > +	for (loop = 0; loop < history->count; loop++) {
> > > +		val = history->states[loop];
> > > +		seq_printf(s, "%s (0x%02x)\n", ltssm_status_string(val), val);
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static int ltssm_trace_open(struct inode *inode, struct file *file)
> > > +{
> > > +	return single_open(file, ltssm_trace_show, inode->i_private);
> > > +}
> > > +
> > >   #define dwc_debugfs_create(name)			\
> > >   debugfs_create_file(#name, 0644, rasdes_debug, pci,	\
> > >   			&dbg_ ## name ## _fops)
> > > @@ -552,6 +584,11 @@ static const struct file_operations dwc_pcie_ltssm_status_ops = {
> > >   	.read = seq_read,
> > >   };
> > > +static const struct file_operations dwc_pcie_ltssm_trace_ops = {
> > > +	.open = ltssm_trace_open,
> > > +	.read = seq_read,
> > > +};
> > > +
> > >   static void dwc_pcie_rasdes_debugfs_deinit(struct dw_pcie *pci)
> > >   {
> > >   	struct dwc_pcie_rasdes_info *rinfo = pci->debugfs->rasdes_info;
> > > @@ -644,6 +681,12 @@ static void dwc_pcie_ltssm_debugfs_init(struct dw_pcie *pci, struct dentry *dir)
> > >   			    &dwc_pcie_ltssm_status_ops);
> > >   }
> > > +static void dwc_pcie_ltssm_trace_debugfs_init(struct dw_pcie *pci, struct dentry *dir)
> > > +{
> > > +	debugfs_create_file("ltssm_trace", 0444, dir, pci,
> > > +			    &dwc_pcie_ltssm_trace_ops);
> > > +}
> > > +
> > >   static int dw_pcie_ptm_check_capability(void *drvdata)
> > >   {
> > >   	struct dw_pcie *pci = drvdata;
> > > @@ -922,6 +965,7 @@ void dwc_pcie_debugfs_init(struct dw_pcie *pci, enum dw_pcie_device_mode mode)
> > >   			err);
> > >   	dwc_pcie_ltssm_debugfs_init(pci, dir);
> > > +	dwc_pcie_ltssm_trace_debugfs_init(pci, dir);
> > >   	pci->mode = mode;
> > >   	pci->ptm_debugfs = pcie_ptm_create_debugfs(pci->dev, pci,
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> > > index 5cd27f5739f1..0df18995b7fe 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > > @@ -395,6 +395,11 @@ enum dw_pcie_ltssm {
> > >   	DW_PCIE_LTSSM_UNKNOWN = 0xFFFFFFFF,
> > >   };
> > > +struct dw_pcie_ltssm_history {
> > > +    enum dw_pcie_ltssm *states;
> > > +    u32 count;
> > > +};
> > > +
> > >   struct dw_pcie_ob_atu_cfg {
> > >   	int index;
> > >   	int type;
> > > @@ -499,6 +504,7 @@ struct dw_pcie_ops {
> > >   			      size_t size, u32 val);
> > >   	bool	(*link_up)(struct dw_pcie *pcie);
> > >   	enum dw_pcie_ltssm (*get_ltssm)(struct dw_pcie *pcie);
> > > +	struct dw_pcie_ltssm_history * (*ltssm_trace)(struct dw_pcie *pcie);
> > >   	int	(*start_link)(struct dw_pcie *pcie);
> > >   	void	(*stop_link)(struct dw_pcie *pcie);
> > >   	int	(*assert_perst)(struct dw_pcie *pcie, bool assert);
> > > -- 
> > > 2.43.0
> > > 
> > > 
> > 
> 
> 

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