In PVH dom0, the gsis don't get registered, but the gsi of
a passthrough device must be configured for it to be able to be
mapped into a domU.

When assign a device to passthrough, proactively setup the gsi
of the device during that process.

Co-developed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
---
 arch/x86/xen/enlighten_pvh.c       | 90 ++++++++++++++++++++++++++++++
 drivers/acpi/pci_irq.c             |  2 +-
 drivers/xen/xen-pciback/pci_stub.c |  8 +++
 include/linux/acpi.h               |  1 +
 include/xen/acpi.h                 |  6 ++
 5 files changed, 106 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
index ada3868c02c2..ecadd966c684 100644
--- a/arch/x86/xen/enlighten_pvh.c
+++ b/arch/x86/xen/enlighten_pvh.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/acpi.h>
 #include <linux/export.h>
+#include <linux/pci.h>
 
 #include <xen/hvc-console.h>
 
@@ -25,6 +26,95 @@
 bool __ro_after_init xen_pvh;
 EXPORT_SYMBOL_GPL(xen_pvh);
 
+typedef struct gsi_info {
+	int gsi;
+	int trigger;
+	int polarity;
+} gsi_info_t;
+
+struct acpi_prt_entry {
+	struct acpi_pci_id	id;
+	u8			pin;
+	acpi_handle		link;
+	u32			index;		/* GSI, or link _CRS index */
+};
+
+static int xen_pvh_get_gsi_info(struct pci_dev *dev,
+								gsi_info_t *gsi_info)
+{
+	int gsi;
+	u8 pin = 0;
+	struct acpi_prt_entry *entry;
+	int trigger = ACPI_LEVEL_SENSITIVE;
+	int polarity = acpi_irq_model == ACPI_IRQ_MODEL_GIC ?
+				      ACPI_ACTIVE_HIGH : ACPI_ACTIVE_LOW;
+
+	if (dev)
+		pin = dev->pin;
+	if (!dev || !pin || !gsi_info)
+		return -EINVAL;
+
+	entry = acpi_pci_irq_lookup(dev, pin);
+	if (entry) {
+		if (entry->link)
+			gsi = acpi_pci_link_allocate_irq(entry->link,
+							 entry->index,
+							 &trigger, &polarity,
+							 NULL);
+		else
+			gsi = entry->index;
+	} else
+		gsi = -1;
+
+	if (gsi < 0)
+		return -EINVAL;
+
+	gsi_info->gsi = gsi;
+	gsi_info->trigger = trigger;
+	gsi_info->polarity = polarity;
+
+	return 0;
+}
+
+static int xen_pvh_setup_gsi(gsi_info_t *gsi_info)
+{
+	struct physdev_setup_gsi setup_gsi;
+
+	if (!gsi_info)
+		return -EINVAL;
+
+	setup_gsi.gsi = gsi_info->gsi;
+	setup_gsi.triggering = (gsi_info->trigger == ACPI_EDGE_SENSITIVE ? 0 : 1);
+	setup_gsi.polarity = (gsi_info->polarity == ACPI_ACTIVE_HIGH ? 0 : 1);
+
+	return HYPERVISOR_physdev_op(PHYSDEVOP_setup_gsi, &setup_gsi);
+}
+
+int xen_pvh_passthrough_gsi(struct pci_dev *dev)
+{
+	int ret;
+	gsi_info_t gsi_info;
+
+	if (!dev)
+		return -EINVAL;
+
+	ret = xen_pvh_get_gsi_info(dev, &gsi_info);
+	if (ret) {
+		xen_raw_printk("Fail to get gsi info!\n");
+		return ret;
+	}
+
+	ret = xen_pvh_setup_gsi(&gsi_info);
+	if (ret == -EEXIST) {
+		xen_raw_printk("Already setup the GSI :%d\n", gsi_info.gsi);
+		ret = 0;
+	} else if (ret)
+		xen_raw_printk("Fail to setup GSI (%d)!\n", gsi_info.gsi);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(xen_pvh_passthrough_gsi);
+
 void __init xen_pvh_init(struct boot_params *boot_params)
 {
 	u32 msr;
diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
index ff30ceca2203..630fe0a34bc6 100644
--- a/drivers/acpi/pci_irq.c
+++ b/drivers/acpi/pci_irq.c
@@ -288,7 +288,7 @@ static int acpi_reroute_boot_interrupt(struct pci_dev *dev,
 }
 #endif /* CONFIG_X86_IO_APIC */
 
-static struct acpi_prt_entry *acpi_pci_irq_lookup(struct pci_dev *dev, int pin)
+struct acpi_prt_entry *acpi_pci_irq_lookup(struct pci_dev *dev, int pin)
 {
 	struct acpi_prt_entry *entry = NULL;
 	struct pci_dev *bridge;
diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
index 46c40ec8a18e..22d4380d2b04 100644
--- a/drivers/xen/xen-pciback/pci_stub.c
+++ b/drivers/xen/xen-pciback/pci_stub.c
@@ -20,6 +20,7 @@
 #include <linux/atomic.h>
 #include <xen/events.h>
 #include <xen/pci.h>
+#include <xen/acpi.h>
 #include <xen/xen.h>
 #include <asm/xen/hypervisor.h>
 #include <xen/interface/physdev.h>
@@ -435,6 +436,13 @@ static int pcistub_init_device(struct pci_dev *dev)
 			goto config_release;
 		pci_restore_state(dev);
 	}
+
+	if (xen_initial_domain() && xen_pvh_domain()) {
+		err = xen_pvh_passthrough_gsi(dev);
+		if (err)
+			goto config_release;
+	}
+
 	/* Now disable the device (this also ensures some private device
 	 * data is setup before we export)
 	 */
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 4db54e928b36..7ea3be981cc3 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -360,6 +360,7 @@ void acpi_unregister_gsi (u32 gsi);
 
 struct pci_dev;
 
+struct acpi_prt_entry *acpi_pci_irq_lookup(struct pci_dev *dev, int pin);
 int acpi_pci_irq_enable (struct pci_dev *dev);
 void acpi_penalize_isa_irq(int irq, int active);
 bool acpi_isa_irq_available(int irq);
diff --git a/include/xen/acpi.h b/include/xen/acpi.h
index b1e11863144d..17c4d37f1e60 100644
--- a/include/xen/acpi.h
+++ b/include/xen/acpi.h
@@ -67,10 +67,16 @@ static inline void xen_acpi_sleep_register(void)
 		acpi_suspend_lowlevel = xen_acpi_suspend_lowlevel;
 	}
 }
+int xen_pvh_passthrough_gsi(struct pci_dev *dev);
 #else
 static inline void xen_acpi_sleep_register(void)
 {
 }
+
+static inline int xen_pvh_passthrough_gsi(struct pci_dev *dev)
+{
+	return -1;
+}
 #endif
 
 #endif	/* _XEN_ACPI_H */
-- 
2.34.1

On Fri, 5 Jan 2024, Jiqian Chen wrote:
> In PVH dom0, the gsis don't get registered, but the gsi of
> a passthrough device must be configured for it to be able to be
> mapped into a domU.
> 
> When assign a device to passthrough, proactively setup the gsi
> of the device during that process.
> 
> Co-developed-by: Huang Rui <ray.huang@amd.com>
> Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
> ---
>  arch/x86/xen/enlighten_pvh.c       | 90 ++++++++++++++++++++++++++++++
>  drivers/acpi/pci_irq.c             |  2 +-
>  drivers/xen/xen-pciback/pci_stub.c |  8 +++
>  include/linux/acpi.h               |  1 +
>  include/xen/acpi.h                 |  6 ++
>  5 files changed, 106 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
> index ada3868c02c2..ecadd966c684 100644
> --- a/arch/x86/xen/enlighten_pvh.c
> +++ b/arch/x86/xen/enlighten_pvh.c
> @@ -1,6 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <linux/acpi.h>
>  #include <linux/export.h>
> +#include <linux/pci.h>
>  
>  #include <xen/hvc-console.h>
>  
> @@ -25,6 +26,95 @@
>  bool __ro_after_init xen_pvh;
>  EXPORT_SYMBOL_GPL(xen_pvh);
>  
> +typedef struct gsi_info {
> +	int gsi;
> +	int trigger;
> +	int polarity;
> +} gsi_info_t;
> +
> +struct acpi_prt_entry {
> +	struct acpi_pci_id	id;
> +	u8			pin;
> +	acpi_handle		link;
> +	u32			index;		/* GSI, or link _CRS index */
> +};
> +
> +static int xen_pvh_get_gsi_info(struct pci_dev *dev,
> +								gsi_info_t *gsi_info)
> +{
> +	int gsi;
> +	u8 pin = 0;
> +	struct acpi_prt_entry *entry;
> +	int trigger = ACPI_LEVEL_SENSITIVE;
> +	int polarity = acpi_irq_model == ACPI_IRQ_MODEL_GIC ?
> +				      ACPI_ACTIVE_HIGH : ACPI_ACTIVE_LOW;
> +
> +	if (dev)
> +		pin = dev->pin;

This is minor, but you can just move the pin = dev->pin after the !dev
check below.

With that change, and assuming the Xen-side and QEMU-side patches are
accepted:

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>




> +	if (!dev || !pin || !gsi_info)
> +		return -EINVAL;
> +
> +	entry = acpi_pci_irq_lookup(dev, pin);
> +	if (entry) {
> +		if (entry->link)
> +			gsi = acpi_pci_link_allocate_irq(entry->link,
> +							 entry->index,
> +							 &trigger, &polarity,
> +							 NULL);
> +		else
> +			gsi = entry->index;
> +	} else
> +		gsi = -1;
> +
> +	if (gsi < 0)
> +		return -EINVAL;
> +
> +	gsi_info->gsi = gsi;
> +	gsi_info->trigger = trigger;
> +	gsi_info->polarity = polarity;
> +
> +	return 0;
> +}
> +
> +static int xen_pvh_setup_gsi(gsi_info_t *gsi_info)
> +{
> +	struct physdev_setup_gsi setup_gsi;
> +
> +	if (!gsi_info)
> +		return -EINVAL;
> +
> +	setup_gsi.gsi = gsi_info->gsi;
> +	setup_gsi.triggering = (gsi_info->trigger == ACPI_EDGE_SENSITIVE ? 0 : 1);
> +	setup_gsi.polarity = (gsi_info->polarity == ACPI_ACTIVE_HIGH ? 0 : 1);
> +
> +	return HYPERVISOR_physdev_op(PHYSDEVOP_setup_gsi, &setup_gsi);
> +}
> +
> +int xen_pvh_passthrough_gsi(struct pci_dev *dev)
> +{
> +	int ret;
> +	gsi_info_t gsi_info;
> +
> +	if (!dev)
> +		return -EINVAL;
> +
> +	ret = xen_pvh_get_gsi_info(dev, &gsi_info);
> +	if (ret) {
> +		xen_raw_printk("Fail to get gsi info!\n");
> +		return ret;
> +	}
> +
> +	ret = xen_pvh_setup_gsi(&gsi_info);
> +	if (ret == -EEXIST) {
> +		xen_raw_printk("Already setup the GSI :%d\n", gsi_info.gsi);
> +		ret = 0;
> +	} else if (ret)
> +		xen_raw_printk("Fail to setup GSI (%d)!\n", gsi_info.gsi);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(xen_pvh_passthrough_gsi);
> +
>  void __init xen_pvh_init(struct boot_params *boot_params)
>  {
>  	u32 msr;
> diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
> index ff30ceca2203..630fe0a34bc6 100644
> --- a/drivers/acpi/pci_irq.c
> +++ b/drivers/acpi/pci_irq.c
> @@ -288,7 +288,7 @@ static int acpi_reroute_boot_interrupt(struct pci_dev *dev,
>  }
>  #endif /* CONFIG_X86_IO_APIC */
>  
> -static struct acpi_prt_entry *acpi_pci_irq_lookup(struct pci_dev *dev, int pin)
> +struct acpi_prt_entry *acpi_pci_irq_lookup(struct pci_dev *dev, int pin)
>  {
>  	struct acpi_prt_entry *entry = NULL;
>  	struct pci_dev *bridge;
> diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
> index 46c40ec8a18e..22d4380d2b04 100644
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -20,6 +20,7 @@
>  #include <linux/atomic.h>
>  #include <xen/events.h>
>  #include <xen/pci.h>
> +#include <xen/acpi.h>
>  #include <xen/xen.h>
>  #include <asm/xen/hypervisor.h>
>  #include <xen/interface/physdev.h>
> @@ -435,6 +436,13 @@ static int pcistub_init_device(struct pci_dev *dev)
>  			goto config_release;
>  		pci_restore_state(dev);
>  	}
> +
> +	if (xen_initial_domain() && xen_pvh_domain()) {
> +		err = xen_pvh_passthrough_gsi(dev);
> +		if (err)
> +			goto config_release;
> +	}
> +
>  	/* Now disable the device (this also ensures some private device
>  	 * data is setup before we export)
>  	 */
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 4db54e928b36..7ea3be981cc3 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -360,6 +360,7 @@ void acpi_unregister_gsi (u32 gsi);
>  
>  struct pci_dev;
>  
> +struct acpi_prt_entry *acpi_pci_irq_lookup(struct pci_dev *dev, int pin);
>  int acpi_pci_irq_enable (struct pci_dev *dev);
>  void acpi_penalize_isa_irq(int irq, int active);
>  bool acpi_isa_irq_available(int irq);
> diff --git a/include/xen/acpi.h b/include/xen/acpi.h
> index b1e11863144d..17c4d37f1e60 100644
> --- a/include/xen/acpi.h
> +++ b/include/xen/acpi.h
> @@ -67,10 +67,16 @@ static inline void xen_acpi_sleep_register(void)
>  		acpi_suspend_lowlevel = xen_acpi_suspend_lowlevel;
>  	}
>  }
> +int xen_pvh_passthrough_gsi(struct pci_dev *dev);
>  #else
>  static inline void xen_acpi_sleep_register(void)
>  {
>  }
> +
> +static inline int xen_pvh_passthrough_gsi(struct pci_dev *dev)
> +{
> +	return -1;
> +}
>  #endif
>  
>  #endif	/* _XEN_ACPI_H */
> -- 
> 2.34.1
>

On 2024/2/23 08:23, Stefano Stabellini wrote:
> On Fri, 5 Jan 2024, Jiqian Chen wrote:
>> In PVH dom0, the gsis don't get registered, but the gsi of
>> a passthrough device must be configured for it to be able to be
>> mapped into a domU.
>>
>> When assign a device to passthrough, proactively setup the gsi
>> of the device during that process.
>>
>> Co-developed-by: Huang Rui <ray.huang@amd.com>
>> Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
>> ---
>>  arch/x86/xen/enlighten_pvh.c       | 90 ++++++++++++++++++++++++++++++
>>  drivers/acpi/pci_irq.c             |  2 +-
>>  drivers/xen/xen-pciback/pci_stub.c |  8 +++
>>  include/linux/acpi.h               |  1 +
>>  include/xen/acpi.h                 |  6 ++
>>  5 files changed, 106 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
>> index ada3868c02c2..ecadd966c684 100644
>> --- a/arch/x86/xen/enlighten_pvh.c
>> +++ b/arch/x86/xen/enlighten_pvh.c
>> @@ -1,6 +1,7 @@
>>  // SPDX-License-Identifier: GPL-2.0
>>  #include <linux/acpi.h>
>>  #include <linux/export.h>
>> +#include <linux/pci.h>
>>  
>>  #include <xen/hvc-console.h>
>>  
>> @@ -25,6 +26,95 @@
>>  bool __ro_after_init xen_pvh;
>>  EXPORT_SYMBOL_GPL(xen_pvh);
>>  
>> +typedef struct gsi_info {
>> +	int gsi;
>> +	int trigger;
>> +	int polarity;
>> +} gsi_info_t;
>> +
>> +struct acpi_prt_entry {
>> +	struct acpi_pci_id	id;
>> +	u8			pin;
>> +	acpi_handle		link;
>> +	u32			index;		/* GSI, or link _CRS index */
>> +};
>> +
>> +static int xen_pvh_get_gsi_info(struct pci_dev *dev,
>> +								gsi_info_t *gsi_info)
>> +{
>> +	int gsi;
>> +	u8 pin = 0;
>> +	struct acpi_prt_entry *entry;
>> +	int trigger = ACPI_LEVEL_SENSITIVE;
>> +	int polarity = acpi_irq_model == ACPI_IRQ_MODEL_GIC ?
>> +				      ACPI_ACTIVE_HIGH : ACPI_ACTIVE_LOW;
>> +
>> +	if (dev)
>> +		pin = dev->pin;
> 
> This is minor, but you can just move the pin = dev->pin after the !dev
> check below.
Will change in next version.

> 
> With that change, and assuming the Xen-side and QEMU-side patches are
> accepted:
> 
> Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Thank you very much!

> 
> 
> 
> 
>> +	if (!dev || !pin || !gsi_info)
>> +		return -EINVAL;
>> +
>> +	entry = acpi_pci_irq_lookup(dev, pin);
>> +	if (entry) {
>> +		if (entry->link)
>> +			gsi = acpi_pci_link_allocate_irq(entry->link,
>> +							 entry->index,
>> +							 &trigger, &polarity,
>> +							 NULL);
>> +		else
>> +			gsi = entry->index;
>> +	} else
>> +		gsi = -1;
>> +
>> +	if (gsi < 0)
>> +		return -EINVAL;
>> +
>> +	gsi_info->gsi = gsi;
>> +	gsi_info->trigger = trigger;
>> +	gsi_info->polarity = polarity;
>> +
>> +	return 0;
>> +}
>> +
>> +static int xen_pvh_setup_gsi(gsi_info_t *gsi_info)
>> +{
>> +	struct physdev_setup_gsi setup_gsi;
>> +
>> +	if (!gsi_info)
>> +		return -EINVAL;
>> +
>> +	setup_gsi.gsi = gsi_info->gsi;
>> +	setup_gsi.triggering = (gsi_info->trigger == ACPI_EDGE_SENSITIVE ? 0 : 1);
>> +	setup_gsi.polarity = (gsi_info->polarity == ACPI_ACTIVE_HIGH ? 0 : 1);
>> +
>> +	return HYPERVISOR_physdev_op(PHYSDEVOP_setup_gsi, &setup_gsi);
>> +}
>> +
>> +int xen_pvh_passthrough_gsi(struct pci_dev *dev)
>> +{
>> +	int ret;
>> +	gsi_info_t gsi_info;
>> +
>> +	if (!dev)
>> +		return -EINVAL;
>> +
>> +	ret = xen_pvh_get_gsi_info(dev, &gsi_info);
>> +	if (ret) {
>> +		xen_raw_printk("Fail to get gsi info!\n");
>> +		return ret;
>> +	}
>> +
>> +	ret = xen_pvh_setup_gsi(&gsi_info);
>> +	if (ret == -EEXIST) {
>> +		xen_raw_printk("Already setup the GSI :%d\n", gsi_info.gsi);
>> +		ret = 0;
>> +	} else if (ret)
>> +		xen_raw_printk("Fail to setup GSI (%d)!\n", gsi_info.gsi);
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(xen_pvh_passthrough_gsi);
>> +
>>  void __init xen_pvh_init(struct boot_params *boot_params)
>>  {
>>  	u32 msr;
>> diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
>> index ff30ceca2203..630fe0a34bc6 100644
>> --- a/drivers/acpi/pci_irq.c
>> +++ b/drivers/acpi/pci_irq.c
>> @@ -288,7 +288,7 @@ static int acpi_reroute_boot_interrupt(struct pci_dev *dev,
>>  }
>>  #endif /* CONFIG_X86_IO_APIC */
>>  
>> -static struct acpi_prt_entry *acpi_pci_irq_lookup(struct pci_dev *dev, int pin)
>> +struct acpi_prt_entry *acpi_pci_irq_lookup(struct pci_dev *dev, int pin)
>>  {
>>  	struct acpi_prt_entry *entry = NULL;
>>  	struct pci_dev *bridge;
>> diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
>> index 46c40ec8a18e..22d4380d2b04 100644
>> --- a/drivers/xen/xen-pciback/pci_stub.c
>> +++ b/drivers/xen/xen-pciback/pci_stub.c
>> @@ -20,6 +20,7 @@
>>  #include <linux/atomic.h>
>>  #include <xen/events.h>
>>  #include <xen/pci.h>
>> +#include <xen/acpi.h>
>>  #include <xen/xen.h>
>>  #include <asm/xen/hypervisor.h>
>>  #include <xen/interface/physdev.h>
>> @@ -435,6 +436,13 @@ static int pcistub_init_device(struct pci_dev *dev)
>>  			goto config_release;
>>  		pci_restore_state(dev);
>>  	}
>> +
>> +	if (xen_initial_domain() && xen_pvh_domain()) {
>> +		err = xen_pvh_passthrough_gsi(dev);
>> +		if (err)
>> +			goto config_release;
>> +	}
>> +
>>  	/* Now disable the device (this also ensures some private device
>>  	 * data is setup before we export)
>>  	 */
>> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
>> index 4db54e928b36..7ea3be981cc3 100644
>> --- a/include/linux/acpi.h
>> +++ b/include/linux/acpi.h
>> @@ -360,6 +360,7 @@ void acpi_unregister_gsi (u32 gsi);
>>  
>>  struct pci_dev;
>>  
>> +struct acpi_prt_entry *acpi_pci_irq_lookup(struct pci_dev *dev, int pin);
>>  int acpi_pci_irq_enable (struct pci_dev *dev);
>>  void acpi_penalize_isa_irq(int irq, int active);
>>  bool acpi_isa_irq_available(int irq);
>> diff --git a/include/xen/acpi.h b/include/xen/acpi.h
>> index b1e11863144d..17c4d37f1e60 100644
>> --- a/include/xen/acpi.h
>> +++ b/include/xen/acpi.h
>> @@ -67,10 +67,16 @@ static inline void xen_acpi_sleep_register(void)
>>  		acpi_suspend_lowlevel = xen_acpi_suspend_lowlevel;
>>  	}
>>  }
>> +int xen_pvh_passthrough_gsi(struct pci_dev *dev);
>>  #else
>>  static inline void xen_acpi_sleep_register(void)
>>  {
>>  }
>> +
>> +static inline int xen_pvh_passthrough_gsi(struct pci_dev *dev)
>> +{
>> +	return -1;
>> +}
>>  #endif
>>  
>>  #endif	/* _XEN_ACPI_H */
>> -- 
>> 2.34.1
>>

-- 
Best regards,
Jiqian Chen.