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 17:12, Krishna Chaitanya Chundru 写道:
> 
> 
> On 1/6/2026 2:48 PM, 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.
>>
>> 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);
> Can we have this as the sysfs, so that if there is some issue in 
> production devices where debugfs is not available,
> we can use this to see LTSSM state figure out the issue.
> 

Thanks for the input. I think the ltssm_trace is debug in nature, just 
like the existing ltssm and rasdes_debug nodes, so it probably fits 
better under debugfs for consistency. Moreover, given most time we
combine rasdes_debug and ltssmm history to debug issues, if we split it
out, we’d end up with two separate debugging areas, which feels a bit
fragmented and less clear.


> - Krishna Chaitanya.
>> +}
>> +
>>   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);
> 
> 


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