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

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

[Shawn Lin]

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);
+}
+
 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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[PATCH 2/2] PCI: dw-rockchip: Add .ltssm_trace() support

[Shawn Lin]

Rockchip platforms provide a 64x4 bytes debug FIFO to trace the
LTSSM history. Any LTSSM change will be recorded. It's userful
for debug purpose, for example link failure, etc.

  cat /sys/kernel/debug/dwc_pcie_a40c00000.pcie/ltssm_trace
    DETECT_QUIET (0x00)
    DETECT_ACT (0x01)
    POLL_ACTIVE (0x02)
    POLL_COMPLIANCE (0x03)
    POLL_ACTIVE (0x02)
    POLL_CONFIG (0x04)
    CFG_LINKWD_START (0x07)
    ...
    RCVRY_IDLE (0x10)
    L0 (0x11)
    L123_SEND_EIDLE (0x13)
    L1_IDLE (0x14)
    RCVRY_LOCK (0x0d)
    ...

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
---
 drivers/pci/controller/dwc/pcie-dw-rockchip.c | 49 +++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
index 352f513ebf03..0f7430e686b2 100644
--- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
+++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
@@ -73,6 +73,17 @@
 #define  PCIE_CLIENT_CDM_RASDES_TBA_L1_1	BIT(4)
 #define  PCIE_CLIENT_CDM_RASDES_TBA_L1_2	BIT(5)
 
+/* Debug FIFO information */
+#define PCIE_CLIENT_DBG_FIFO_MODE_CON	0x310
+#define  PCIE_CLIENT_DBG_EN		0xffff0007
+#define PCIE_CLIENT_DBG_FIFO_PTN_HIT_D0	0x320
+#define PCIE_CLIENT_DBG_FIFO_PTN_HIT_D1	0x324
+#define PCIE_CLIENT_DBG_FIFO_TRN_HIT_D0	0x328
+#define PCIE_CLIENT_DBG_FIFO_TRN_HIT_D1	0x32c
+#define  PCIE_CLIENT_DBG_TRANSITION_DATA 0xffff0000
+#define PCIE_CLIENT_DBG_FIFO_STATUS	0x350
+#define PCIE_DBG_LTSSM_HISTORY_CNT	64
+
 /* Hot Reset Control Register */
 #define PCIE_CLIENT_HOT_RESET_CTRL	0x180
 #define  PCIE_LTSSM_APP_DLY2_EN		BIT(1)
@@ -96,6 +107,7 @@ struct rockchip_pcie {
 	struct irq_domain *irq_domain;
 	const struct rockchip_pcie_of_data *data;
 	bool supports_clkreq;
+	struct dw_pcie_ltssm_history ltssm_history;
 };
 
 struct rockchip_pcie_of_data {
@@ -206,6 +218,34 @@ static enum dw_pcie_ltssm rockchip_pcie_get_ltssm(struct dw_pcie *pci)
 	return rockchip_pcie_get_ltssm_reg(rockchip) & PCIE_LTSSM_STATUS_MASK;
 }
 
+static void rockchip_pcie_enable_ltssm_trace(struct rockchip_pcie *rockchip)
+{
+        rockchip_pcie_writel_apb(rockchip, PCIE_CLIENT_DBG_TRANSITION_DATA,
+				 PCIE_CLIENT_DBG_FIFO_PTN_HIT_D0);
+        rockchip_pcie_writel_apb(rockchip, PCIE_CLIENT_DBG_TRANSITION_DATA,
+				 PCIE_CLIENT_DBG_FIFO_PTN_HIT_D1);
+        rockchip_pcie_writel_apb(rockchip, PCIE_CLIENT_DBG_TRANSITION_DATA,
+				 PCIE_CLIENT_DBG_FIFO_TRN_HIT_D0);
+        rockchip_pcie_writel_apb(rockchip, PCIE_CLIENT_DBG_TRANSITION_DATA,
+				 PCIE_CLIENT_DBG_FIFO_TRN_HIT_D1);
+        rockchip_pcie_writel_apb(rockchip, PCIE_CLIENT_DBG_EN,
+				 PCIE_CLIENT_DBG_FIFO_MODE_CON);
+}
+
+static struct dw_pcie_ltssm_history* rockchip_pcie_ltssm_trace(struct dw_pcie *pci)
+{
+	struct rockchip_pcie *rockchip = to_rockchip_pcie(pci);
+	u32 loop, val;
+
+	for (loop = 0; loop < PCIE_DBG_LTSSM_HISTORY_CNT; loop++) {
+		val = rockchip_pcie_readl_apb(rockchip, PCIE_CLIENT_DBG_FIFO_STATUS) &
+					PCIE_LTSSM_STATUS_MASK;
+		rockchip->ltssm_history.states[loop] = val;
+	}
+
+	return &rockchip->ltssm_history;
+}
+
 static void rockchip_pcie_enable_ltssm(struct rockchip_pcie *rockchip)
 {
 	rockchip_pcie_writel_apb(rockchip, PCIE_CLIENT_ENABLE_LTSSM,
@@ -277,6 +317,8 @@ static int rockchip_pcie_start_link(struct dw_pcie *pci)
 	/* Reset device */
 	gpiod_set_value_cansleep(rockchip->rst_gpio, 0);
 
+	rockchip_pcie_enable_ltssm_trace(rockchip);
+
 	rockchip_pcie_enable_ltssm(rockchip);
 
 	/*
@@ -506,6 +548,7 @@ static const struct dw_pcie_ops dw_pcie_ops = {
 	.start_link = rockchip_pcie_start_link,
 	.stop_link = rockchip_pcie_stop_link,
 	.get_ltssm = rockchip_pcie_get_ltssm,
+	.ltssm_trace = rockchip_pcie_ltssm_trace,
 };
 
 static irqreturn_t rockchip_pcie_ep_sys_irq_thread(int irq, void *arg)
@@ -645,6 +688,12 @@ static int rockchip_pcie_probe(struct platform_device *pdev)
 	rockchip->pci.ops = &dw_pcie_ops;
 	rockchip->data = data;
 
+	rockchip->ltssm_history.count = PCIE_DBG_LTSSM_HISTORY_CNT;
+	rockchip->ltssm_history.states = devm_kzalloc(dev,
+			PCIE_DBG_LTSSM_HISTORY_CNT * sizeof(u32), GFP_KERNEL);
+	if (!rockchip->ltssm_history.states)
+		return -ENOMEM;
+
 	/* Default N_FTS value (210) is broken, override it to 255 */
 	rockchip->pci.n_fts[0] = 255; /* Gen1 */
 	rockchip->pci.n_fts[1] = 255; /* Gen2+ */
-- 
2.43.0


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

[Krishna Chaitanya Chundru]

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.

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

[Shawn Lin]

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

[Krishna Chaitanya Chundru]

On 1/7/2026 3:11 PM, Shawn Lin wrote:
> 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. 
Rasdes has statistics and err injection along with debug feature, we can 
have them
as debugfs only since they will not help in debugging production issues. 
For others like
ltssm, lane_detect & rx_valid we can have in sysfs.

- Krishna Chaitanya.
>
>
>> - 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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Re: [PATCH 1/2] PCI: dwc: Add LTSSM tracing support to debugfs

[Manivannan Sadhasivam]

On Wed, Jan 07, 2026 at 02:42:38PM +0530, Krishna Chaitanya Chundru wrote:
> 
> 
> 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.

'figure out' means 'debug'. If you want to debug an issue, you need to enable
debugfs. You should not introduce random sysfs ABI for debug interfaces.

- Mani

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

[Shawn Lin]

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

[Shawn Lin]

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

[Manivannan Sadhasivam]

On Thu, Jan 08, 2026 at 12:58:28PM +0800, Shawn Lin wrote:
> 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

Is this an existing file? I couldn't see it. But anyway, I think it would be
better to create a separate file for controller drivers. PCI core may end up
having its own tracepoint in the future and mixing both will lead to confusion.

> 
> 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

/sys/kernel/debug/tracing/events/pci_controller/pcie_ltssm_state_transition/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

Can you print the state name using dw_pcie_ltssm_status_string() with:
https://lore.kernel.org/linux-pci/20260107-pci-dwc-suspend-rework-v4-2-9b5f3c72df0a@oss.qualcomm.com/

Also you can remove 'PCIe' at the end.

Rest LGTM, thanks!

- Mani

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