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From: Shawn Lin <shawn.lin@rock-chips.com>
To: Manivannan Sadhasivam <mani@kernel.org>
Cc: shawn.lin@rock-chips.com, Jingoo Han <jingoohan1@gmail.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	linux-rockchip@lists.infradead.org,
	Niklas Cassel <cassel@kernel.org>,
	linux-pci@vger.kernel.org
Subject: Re: [PATCH 1/2] PCI: dwc: Add LTSSM tracing support to debugfs
Date: Thu, 8 Jan 2026 12:58:28 +0800	[thread overview]
Message-ID: <70b6e8c9-8dbe-484a-b8a8-aeb7380b6ca2@rock-chips.com> (raw)
In-Reply-To: <lhshuxj4aztwbernypwgaxkdtxzonzydzipu63mspbqfygyrvy@nggpj7vwsw7n>

在 2026/01/08 星期四 12:49, Manivannan Sadhasivam 写道:
> 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.
> 

I did a quick convention by adding it to the existing 
include/trace/events/pci.h

The TRACE_EVENT is called pcie_ltssm_state_change, making it not just
for dwc-based but for all possible coming host drivers and the output
looks like below. Is that the way you expected?

root@debian:/#echo 1 > 
/sys/kernel/debug/tracing/events/pci/pcie_ltssm_state_change/enable
root@debian:/# cat /sys/kernel/debug/tracing/trace
# tracer: nop
#
# entries-in-buffer/entries-written: 572/572   #P:8
#
#                                _-----=> irqs-off/BH-disabled
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| / _-=> migrate-disable
#                              |||| /     delay
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |

...
      kworker/1:1-109     [001] .....     4.719968: ltssm_state_change: 
dev: a40000000.pcie state: 0x0d rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719969: ltssm_state_change: 
dev: a40000000.pcie state: 0x0f rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719970: ltssm_state_change: 
dev: a40000000.pcie state: 0x10 rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719970: ltssm_state_change: 
dev: a40000000.pcie state: 0x11 rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719971: ltssm_state_change: 
dev: a40000000.pcie state: 0x13 rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719972: ltssm_state_change: 
dev: a40000000.pcie state: 0x14 rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719973: ltssm_state_change: 
dev: a40000000.pcie state: 0x0d rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719973: ltssm_state_change: 
dev: a40000000.pcie state: 0x0f rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719974: ltssm_state_change: 
dev: a40000000.pcie state: 0x10 rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719975: ltssm_state_change: 
dev: a40000000.pcie state: 0x11 rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719975: ltssm_state_change: 
dev: a40000000.pcie state: 0x13 rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719976: ltssm_state_change: 
dev: a40000000.pcie state: 0x14 rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719977: ltssm_state_change: 
dev: a40000000.pcie state: 0x0d rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719977: ltssm_state_change: 
dev: a40000000.pcie state: 0x0f rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719978: ltssm_state_change: 
dev: a40000000.pcie state: 0x10 rate: 8.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719979: ltssm_state_change: 
dev: a40000000.pcie state: 0x11 rate: 5.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719980: ltssm_state_change: 
dev: a40000000.pcie state: 0x13 rate: 5.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719980: ltssm_state_change: 
dev: a40000000.pcie state: 0x14 rate: 5.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719981: ltssm_state_change: 
dev: a40000000.pcie state: 0x0d rate: 5.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719982: ltssm_state_change: 
dev: a40000000.pcie state: 0x0f rate: 5.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719982: ltssm_state_change: 
dev: a40000000.pcie state: 0x10 rate: 5.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719983: ltssm_state_change: 
dev: a40000000.pcie state: 0x11 rate: 5.0 GT/s PCIe
      kworker/1:1-109     [001] .....     4.719984: ltssm_state_change: 
dev: a40000000.pcie state: 0x13 rate: 5.0 GT/s PCIe


> - Mani
> 
>>> - 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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  reply	other threads:[~2026-01-08  4:58 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-01-06  9:18 [PATCH 1/2] PCI: dwc: Add LTSSM tracing support to debugfs Shawn Lin
2026-01-06  9:18 ` [PATCH 2/2] PCI: dw-rockchip: Add .ltssm_trace() support Shawn Lin
2026-01-07  9:12 ` [PATCH 1/2] PCI: dwc: Add LTSSM tracing support to debugfs Krishna Chaitanya Chundru
2026-01-07  9:41   ` Shawn Lin
2026-01-07 10:09     ` Krishna Chaitanya Chundru
2026-01-07 12:40   ` Manivannan Sadhasivam
2026-01-07 12:41 ` Manivannan Sadhasivam
2026-01-08  1:01   ` Shawn Lin
2026-01-08  4:49     ` Manivannan Sadhasivam
2026-01-08  4:58       ` Shawn Lin [this message]
2026-01-08 17:05         ` Manivannan Sadhasivam

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