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

[Shawn Lin <shawn.lin@rock-chips.com>]

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?

> - Mani
> 
>> Signed-off-by: Shawn Lin <shawn.lin@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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