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

[Manivannan Sadhasivam]

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?

- 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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