[PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[hongxing.zhu]

From: Richard Zhu <hongxing.zhu@nxp.com>

Some platforms like i.MX power off their PCIe RC controllers during
system suspend, requiring full re-initialization on resume. These
platforms need to enter L2 state to properly notify endpoints before
power loss.

According to PCIe base spec r7.0, sec 5.2, the system software should
transition the device into D3Hot before broadcasting the PME_Turn_Off
message to initiate L2 entry. However, some endpoint devices fail the
D3cold capability check in pci_host_common_d3cold_possible(), which
would normally prevent L2 entry.

For platforms where the RC loses power during suspend, L2 entry is
essential regardless of D3cold support, as the link will be lost anyway.
Add a suspend_poweroff flag to force L2 entry in such cases, and enable
it for i.MX PCIe controllers.

Note: This violates the spec requirement that devices be in D3Hot before
PME_Turn_Off, but is necessary for proper operation on platforms with RC
power loss during suspend.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
---
Changes in v2:
- Rename the new added flag.
- Update commit description and comments.

---
 drivers/pci/controller/dwc/pci-imx6.c             | 11 +++++++++++
 drivers/pci/controller/dwc/pcie-designware-host.c | 10 ++++++++--
 drivers/pci/controller/dwc/pcie-designware.h      |  8 ++++++++
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 98e1db751132a..5a43bf396521b 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -1957,6 +1957,17 @@ static int imx_pcie_probe(struct platform_device *pdev)
 		 */
 		imx_pcie_add_lut_by_rid(imx_pcie, 0);
 	} else {
+		/*
+		 * i.MX RC is powered off during suspend, requiring L2 entry
+		 * to notify endpoints before power loss. Some endpoints fail
+		 * the D3cold capability check, which would normally prevent
+		 * L2 entry. Force L2 entry anyway since the link will be lost
+		 * when RC powers off.
+		 *
+		 * Note: Per PCIe spec r7.0 sec 5.2, devices should be in D3Hot
+		 * before PME_Turn_Off. This may not be guaranteed here.
+		 */
+		pci->pp.suspend_poweroff = true;
 		if (imx_check_flag(imx_pcie, IMX_PCIE_FLAG_SKIP_L23_READY))
 			pci->pp.skip_l23_ready = true;
 		if (imx_check_flag(imx_pcie, IMX_PCIE_FLAG_KEEP_MSI_CAP))
diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 06722259d2e37..95a31d65e1ca9 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -1222,14 +1222,20 @@ static int dw_pcie_pme_turn_off(struct dw_pcie *pci)
 
 int dw_pcie_suspend_noirq(struct dw_pcie *pci)
 {
-	bool pme_capable = false;
+	bool d3cold, pme_capable = false;
 	int ret = 0;
 	u32 val;
 
 	if (!dw_pcie_link_up(pci))
 		goto stop_link;
 
-	if (!pci_host_common_d3cold_possible(pci->pp.bridge, &pme_capable))
+	d3cold = pci_host_common_d3cold_possible(pci->pp.bridge, &pme_capable);
+	/*
+	 * Enter L2 if D3cold is possible, or if the platform loses RC power
+	 * during suspend (in which case L2 entry is required to notify
+	 * endpoints before power loss, regardless of D3cold support).
+	 */
+	if (!d3cold && !pci->pp.suspend_poweroff)
 		return 0;
 
 	if (pci->pp.ops->pme_turn_off) {
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index de4b245b1758c..3ce7d30d9a4d5 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -471,6 +471,14 @@ struct dw_pcie_rp {
 	bool			native_ecam;
 	bool                    skip_l23_ready;
 	bool			skip_pwrctrl_off;
+	/*
+	 * suspend_poweroff: Force L2 entry during suspend even when D3cold
+	 * capability check fails. Used on platforms where RC loses power
+	 * during suspend and must notify endpoints via L2 entry before
+	 * power loss. May not meet PCIe spec requirement for devices to be
+	 * in D3Hot before PME_Turn_Off.
+	 */
+	bool                    suspend_poweroff;
 };
 
 struct dw_pcie_ep_ops {
-- 
2.34.1

Re: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[Manivannan Sadhasivam]

On Fri, 17 Jul 2026 15:41:21 +0800, hongxing.zhu@oss.nxp.com wrote:
> Some platforms like i.MX power off their PCIe RC controllers during
> system suspend, requiring full re-initialization on resume. These
> platforms need to enter L2 state to properly notify endpoints before
> power loss.
> 
> According to PCIe base spec r7.0, sec 5.2, the system software should
> transition the device into D3Hot before broadcasting the PME_Turn_Off
> message to initiate L2 entry. However, some endpoint devices fail the
> D3cold capability check in pci_host_common_d3cold_possible(), which
> would normally prevent L2 entry.
> 
> [...]

Applied, thanks!

[1/1] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss
      commit: 5a53462aba161e809de90d45f2a39510a88b6ede

Best regards,
-- 
மணிவண்ணன் சதாசிவம்

Re: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[Bjorn Helgaas]

On Fri, Jul 17, 2026 at 03:41:21PM +0800, hongxing.zhu@oss.nxp.com wrote:
> From: Richard Zhu <hongxing.zhu@nxp.com>
> 
> Some platforms like i.MX power off their PCIe RC controllers during
> system suspend, requiring full re-initialization on resume. These
> platforms need to enter L2 state to properly notify endpoints before
> power loss.
> 
> According to PCIe base spec r7.0, sec 5.2, the system software should
> transition the device into D3Hot before broadcasting the PME_Turn_Off
> message to initiate L2 entry. However, some endpoint devices fail the
> D3cold capability check in pci_host_common_d3cold_possible(), which
> would normally prevent L2 entry.

Wakeup devices that don't support PME from D3cold will fail the D3cold
capability check, but I don't think those are the problem you're
solving.

This appears to handle devices that are not in D3hot, and that's not a
property of the endpoint; it's a property of its driver.  Is the
problem here that some driver didn't put its device in D3hot?

> For platforms where the RC loses power during suspend, L2 entry is
> essential regardless of D3cold support, as the link will be lost anyway.
> Add a suspend_poweroff flag to force L2 entry in such cases, and enable
> it for i.MX PCIe controllers.
> 
> Note: This violates the spec requirement that devices be in D3Hot before
> PME_Turn_Off, but is necessary for proper operation on platforms with RC
> power loss during suspend.

If the device isn't in D3hot, it may still be active, and I think the
PME_Turn_Off will abort any DMAs in progress, which doesn't sound like
proper operation of the endpoint.

> Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
> ---
> Changes in v2:
> - Rename the new added flag.
> - Update commit description and comments.
> 
> ---
>  drivers/pci/controller/dwc/pci-imx6.c             | 11 +++++++++++
>  drivers/pci/controller/dwc/pcie-designware-host.c | 10 ++++++++--
>  drivers/pci/controller/dwc/pcie-designware.h      |  8 ++++++++
>  3 files changed, 27 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 98e1db751132a..5a43bf396521b 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -1957,6 +1957,17 @@ static int imx_pcie_probe(struct platform_device *pdev)
>  		 */
>  		imx_pcie_add_lut_by_rid(imx_pcie, 0);
>  	} else {
> +		/*
> +		 * i.MX RC is powered off during suspend, requiring L2 entry
> +		 * to notify endpoints before power loss. Some endpoints fail
> +		 * the D3cold capability check, which would normally prevent
> +		 * L2 entry. Force L2 entry anyway since the link will be lost
> +		 * when RC powers off.
> +		 *
> +		 * Note: Per PCIe spec r7.0 sec 5.2, devices should be in D3Hot
> +		 * before PME_Turn_Off. This may not be guaranteed here.
> +		 */
> +		pci->pp.suspend_poweroff = true;
>  		if (imx_check_flag(imx_pcie, IMX_PCIE_FLAG_SKIP_L23_READY))
>  			pci->pp.skip_l23_ready = true;
>  		if (imx_check_flag(imx_pcie, IMX_PCIE_FLAG_KEEP_MSI_CAP))
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 06722259d2e37..95a31d65e1ca9 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -1222,14 +1222,20 @@ static int dw_pcie_pme_turn_off(struct dw_pcie *pci)
>  
>  int dw_pcie_suspend_noirq(struct dw_pcie *pci)
>  {
> -	bool pme_capable = false;
> +	bool d3cold, pme_capable = false;
>  	int ret = 0;
>  	u32 val;
>  
>  	if (!dw_pcie_link_up(pci))
>  		goto stop_link;
>  
> -	if (!pci_host_common_d3cold_possible(pci->pp.bridge, &pme_capable))
> +	d3cold = pci_host_common_d3cold_possible(pci->pp.bridge, &pme_capable);
> +	/*
> +	 * Enter L2 if D3cold is possible, or if the platform loses RC power
> +	 * during suspend (in which case L2 entry is required to notify
> +	 * endpoints before power loss, regardless of D3cold support).
> +	 */
> +	if (!d3cold && !pci->pp.suspend_poweroff)
>  		return 0;
>  
>  	if (pci->pp.ops->pme_turn_off) {
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index de4b245b1758c..3ce7d30d9a4d5 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -471,6 +471,14 @@ struct dw_pcie_rp {
>  	bool			native_ecam;
>  	bool                    skip_l23_ready;
>  	bool			skip_pwrctrl_off;
> +	/*
> +	 * suspend_poweroff: Force L2 entry during suspend even when D3cold
> +	 * capability check fails. Used on platforms where RC loses power
> +	 * during suspend and must notify endpoints via L2 entry before
> +	 * power loss. May not meet PCIe spec requirement for devices to be
> +	 * in D3Hot before PME_Turn_Off.
> +	 */
> +	bool                    suspend_poweroff;
>  };
>  
>  struct dw_pcie_ep_ops {
> -- 
> 2.34.1
> 

RE: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[Hongxing Zhu (OSS)]

> -----Original Message-----
> From: Bjorn Helgaas <helgaas@kernel.org>
> Sent: Thursday, July 30, 2026 6:30 AM
> To: Hongxing Zhu (OSS) <hongxing.zhu@oss.nxp.com>
> Cc: Frank Li <frank.li@nxp.com>; l.stach@pengutronix.de; lpieralisi@kernel.org;
> kwilczynski@kernel.org; mani@kernel.org; robh@kernel.org;
> bhelgaas@google.com; s.hauer@pengutronix.de; kernel@pengutronix.de;
> festevam@gmail.com; linux-pci@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; imx@lists.linux.dev; linux-kernel@vger.kernel.org;
> Hongxing Zhu <hongxing.zhu@nxp.com>
> Subject: Re: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with
> RC power loss
> 
> On Fri, Jul 17, 2026 at 03:41:21PM +0800, hongxing.zhu@oss.nxp.com wrote:
> > From: Richard Zhu <hongxing.zhu@nxp.com>
> >
> > Some platforms like i.MX power off their PCIe RC controllers during
> > system suspend, requiring full re-initialization on resume. These
> > platforms need to enter L2 state to properly notify endpoints before
> > power loss.
> >
> > According to PCIe base spec r7.0, sec 5.2, the system software should
> > transition the device into D3Hot before broadcasting the PME_Turn_Off
> > message to initiate L2 entry. However, some endpoint devices fail the
> > D3cold capability check in pci_host_common_d3cold_possible(), which
> > would normally prevent L2 entry.
> 
> Wakeup devices that don't support PME from D3cold will fail the D3cold capability
> check, but I don't think those are the problem you're solving.
> 
You're right.

> This appears to handle devices that are not in D3hot, and that's not a property of
> the endpoint; it's a property of its driver.  Is the problem here that some driver
> didn't put its device in D3hot?
> 
I observed some endpoint devices failing the D3cold capability check, but I
haven't identified the root cause.

> > For platforms where the RC loses power during suspend, L2 entry is
> > essential regardless of D3cold support, as the link will be lost anyway.
> > Add a suspend_poweroff flag to force L2 entry in such cases, and
> > enable it for i.MX PCIe controllers.
> >
> > Note: This violates the spec requirement that devices be in D3Hot
> > before PME_Turn_Off, but is necessary for proper operation on
> > platforms with RC power loss during suspend.
> 
> If the device isn't in D3hot, it may still be active, and I think the PME_Turn_Off
> will abort any DMAs in progress, which doesn't sound like proper operation of the
> endpoint.
You're correct - this isn't ideal for endpoint operation. However, on i.MX
platforms, the RC controller will lose power during system suspend
regardless. Without sending PME_Turn_Off, endpoints would have no notification
before the link abruptly goes down.

This patch adds a flag to force L2 entry for such platforms, choosing to
notify endpoints (even if not ideal) rather than having the link drop
unexpectedly. I'm appreciated for suggestions if there's a better approach to
handle this scenario.

Thanks a lot.
Best Regards
Richard Zhu
> 
> > Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
> > ---
> > Changes in v2:
> > - Rename the new added flag.
> > - Update commit description and comments.
> >
> > ---
> >  drivers/pci/controller/dwc/pci-imx6.c             | 11 +++++++++++
> >  drivers/pci/controller/dwc/pcie-designware-host.c | 10 ++++++++--
> >  drivers/pci/controller/dwc/pcie-designware.h      |  8 ++++++++
> >  3 files changed, 27 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index 98e1db751132a..5a43bf396521b 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -1957,6 +1957,17 @@ static int imx_pcie_probe(struct platform_device
> *pdev)
> >  		 */
> >  		imx_pcie_add_lut_by_rid(imx_pcie, 0);
> >  	} else {
> > +		/*
> > +		 * i.MX RC is powered off during suspend, requiring L2 entry
> > +		 * to notify endpoints before power loss. Some endpoints fail
> > +		 * the D3cold capability check, which would normally prevent
> > +		 * L2 entry. Force L2 entry anyway since the link will be lost
> > +		 * when RC powers off.
> > +		 *
> > +		 * Note: Per PCIe spec r7.0 sec 5.2, devices should be in D3Hot
> > +		 * before PME_Turn_Off. This may not be guaranteed here.
> > +		 */
> > +		pci->pp.suspend_poweroff = true;
> >  		if (imx_check_flag(imx_pcie,
> IMX_PCIE_FLAG_SKIP_L23_READY))
> >  			pci->pp.skip_l23_ready = true;
> >  		if (imx_check_flag(imx_pcie, IMX_PCIE_FLAG_KEEP_MSI_CAP))
> diff
> > --git a/drivers/pci/controller/dwc/pcie-designware-host.c
> > b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 06722259d2e37..95a31d65e1ca9 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -1222,14 +1222,20 @@ static int dw_pcie_pme_turn_off(struct dw_pcie
> > *pci)
> >
> >  int dw_pcie_suspend_noirq(struct dw_pcie *pci)  {
> > -	bool pme_capable = false;
> > +	bool d3cold, pme_capable = false;
> >  	int ret = 0;
> >  	u32 val;
> >
> >  	if (!dw_pcie_link_up(pci))
> >  		goto stop_link;
> >
> > -	if (!pci_host_common_d3cold_possible(pci->pp.bridge, &pme_capable))
> > +	d3cold = pci_host_common_d3cold_possible(pci->pp.bridge,
> &pme_capable);
> > +	/*
> > +	 * Enter L2 if D3cold is possible, or if the platform loses RC power
> > +	 * during suspend (in which case L2 entry is required to notify
> > +	 * endpoints before power loss, regardless of D3cold support).
> > +	 */
> > +	if (!d3cold && !pci->pp.suspend_poweroff)
> >  		return 0;
> >
> >  	if (pci->pp.ops->pme_turn_off) {
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.h
> > b/drivers/pci/controller/dwc/pcie-designware.h
> > index de4b245b1758c..3ce7d30d9a4d5 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > @@ -471,6 +471,14 @@ struct dw_pcie_rp {
> >  	bool			native_ecam;
> >  	bool                    skip_l23_ready;
> >  	bool			skip_pwrctrl_off;
> > +	/*
> > +	 * suspend_poweroff: Force L2 entry during suspend even when D3cold
> > +	 * capability check fails. Used on platforms where RC loses power
> > +	 * during suspend and must notify endpoints via L2 entry before
> > +	 * power loss. May not meet PCIe spec requirement for devices to be
> > +	 * in D3Hot before PME_Turn_Off.
> > +	 */
> > +	bool                    suspend_poweroff;
> >  };
> >
> >  struct dw_pcie_ep_ops {
> > --
> > 2.34.1
> >

Re: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[Bjorn Helgaas]

On Thu, Jul 30, 2026 at 08:16:36AM +0000, Hongxing Zhu (OSS) wrote:
> > -----Original Message-----
> > From: Bjorn Helgaas <helgaas@kernel.org>
> > Sent: Thursday, July 30, 2026 6:30 AM
> ...

> > On Fri, Jul 17, 2026 at 03:41:21PM +0800, hongxing.zhu@oss.nxp.com wrote:
> > > From: Richard Zhu <hongxing.zhu@nxp.com>
> > >
> > > Some platforms like i.MX power off their PCIe RC controllers during
> > > system suspend, requiring full re-initialization on resume. These
> > > platforms need to enter L2 state to properly notify endpoints before
> > > power loss.
> > >
> > > According to PCIe base spec r7.0, sec 5.2, the system software should
> > > transition the device into D3Hot before broadcasting the PME_Turn_Off
> > > message to initiate L2 entry. However, some endpoint devices fail the
> > > D3cold capability check in pci_host_common_d3cold_possible(), which
> > > would normally prevent L2 entry.
> > 
> > Wakeup devices that don't support PME from D3cold will fail the
> > D3cold capability check, but I don't think those are the problem
> > you're solving.
> > 
> You're right.
> 
> > This appears to handle devices that are not in D3hot, and that's
> > not a property of the endpoint; it's a property of its driver.  Is
> > the problem here that some driver didn't put its device in D3hot?
> > 
> I observed some endpoint devices failing the D3cold capability
> check, but I haven't identified the root cause.

Seems like some instrumentation in pci_host_common_d3cold_possible()
could tell us which devices/drivers are relevant.

> > > For platforms where the RC loses power during suspend, L2 entry
> > > is essential regardless of D3cold support, as the link will be
> > > lost anyway.  Add a suspend_poweroff flag to force L2 entry in
> > > such cases, and enable it for i.MX PCIe controllers.
> > >
> > > Note: This violates the spec requirement that devices be in
> > > D3Hot before PME_Turn_Off, but is necessary for proper operation
> > > on platforms with RC power loss during suspend.
> > 
> > If the device isn't in D3hot, it may still be active, and I think
> > the PME_Turn_Off will abort any DMAs in progress, which doesn't
> > sound like proper operation of the endpoint.
>
> You're correct - this isn't ideal for endpoint operation. However,
> on i.MX platforms, the RC controller will lose power during system
> suspend regardless. Without sending PME_Turn_Off, endpoints would
> have no notification before the link abruptly goes down.

The PME_Turn_Off is some notification, but I don't think the endpoint
can do DMA or MSI, so its driver won't be involved.  It may be able to
do things internally, e.g., write caches to an SSD or transmit packets
from its internal buffers.  But I think it might still lose power in
the middle of operations like that, so it doesn't sound reliable.

> This patch adds a flag to force L2 entry for such platforms,
> choosing to notify endpoints (even if not ideal) rather than having
> the link drop unexpectedly. I'm appreciated for suggestions if
> there's a better approach to handle this scenario.

Mani recently added pci_suspend_retains_context(), and I think it
returns "true" on i.MX.  But if the RC is powered off and all the
devices need full re-initialization on resume, it sounds like it
*should* return "false".

Re: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[Manivannan Sadhasivam]

On Thu, Jul 30, 2026 at 07:09:13AM -0500, Bjorn Helgaas wrote:
> On Thu, Jul 30, 2026 at 08:16:36AM +0000, Hongxing Zhu (OSS) wrote:
> > > -----Original Message-----
> > > From: Bjorn Helgaas <helgaas@kernel.org>
> > > Sent: Thursday, July 30, 2026 6:30 AM
> > ...
> 
> > > On Fri, Jul 17, 2026 at 03:41:21PM +0800, hongxing.zhu@oss.nxp.com wrote:
> > > > From: Richard Zhu <hongxing.zhu@nxp.com>
> > > >
> > > > Some platforms like i.MX power off their PCIe RC controllers during
> > > > system suspend, requiring full re-initialization on resume. These
> > > > platforms need to enter L2 state to properly notify endpoints before
> > > > power loss.
> > > >
> > > > According to PCIe base spec r7.0, sec 5.2, the system software should
> > > > transition the device into D3Hot before broadcasting the PME_Turn_Off
> > > > message to initiate L2 entry. However, some endpoint devices fail the
> > > > D3cold capability check in pci_host_common_d3cold_possible(), which
> > > > would normally prevent L2 entry.
> > > 
> > > Wakeup devices that don't support PME from D3cold will fail the
> > > D3cold capability check, but I don't think those are the problem
> > > you're solving.
> > > 
> > You're right.
> > 
> > > This appears to handle devices that are not in D3hot, and that's
> > > not a property of the endpoint; it's a property of its driver.  Is
> > > the problem here that some driver didn't put its device in D3hot?
> > > 
> > I observed some endpoint devices failing the D3cold capability
> > check, but I haven't identified the root cause.
> 
> Seems like some instrumentation in pci_host_common_d3cold_possible()
> could tell us which devices/drivers are relevant.
> 
> > > > For platforms where the RC loses power during suspend, L2 entry
> > > > is essential regardless of D3cold support, as the link will be
> > > > lost anyway.  Add a suspend_poweroff flag to force L2 entry in
> > > > such cases, and enable it for i.MX PCIe controllers.
> > > >
> > > > Note: This violates the spec requirement that devices be in
> > > > D3Hot before PME_Turn_Off, but is necessary for proper operation
> > > > on platforms with RC power loss during suspend.
> > > 
> > > If the device isn't in D3hot, it may still be active, and I think
> > > the PME_Turn_Off will abort any DMAs in progress, which doesn't
> > > sound like proper operation of the endpoint.
> >
> > You're correct - this isn't ideal for endpoint operation. However,
> > on i.MX platforms, the RC controller will lose power during system
> > suspend regardless. Without sending PME_Turn_Off, endpoints would
> > have no notification before the link abruptly goes down.
> 
> The PME_Turn_Off is some notification, but I don't think the endpoint
> can do DMA or MSI, so its driver won't be involved.  It may be able to
> do things internally, e.g., write caches to an SSD or transmit packets
> from its internal buffers.  But I think it might still lose power in
> the middle of operations like that, so it doesn't sound reliable.
> 
> > This patch adds a flag to force L2 entry for such platforms,
> > choosing to notify endpoints (even if not ideal) rather than having
> > the link drop unexpectedly. I'm appreciated for suggestions if
> > there's a better approach to handle this scenario.
> 
> Mani recently added pci_suspend_retains_context(), and I think it
> returns "true" on i.MX.  But if the RC is powered off and all the
> devices need full re-initialization on resume, it sounds like it
> *should* return "false".

Right. pci_suspend_retains_context() was added just for that purpose of telling
client drivers to prepare for context loss. So if this API returns 'false', then
they should not hold the device in D0.

- Mani

-- 
மணிவண்ணன் சதாசிவம்

RE: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[Hongxing Zhu (OSS)]

> -----Original Message-----
> From: Manivannan Sadhasivam <mani@kernel.org>
> Sent: Monday, August 3, 2026 11:33 PM
> To: Bjorn Helgaas <helgaas@kernel.org>
> Cc: Hongxing Zhu (OSS) <hongxing.zhu@oss.nxp.com>; Frank Li
> <frank.li@nxp.com>; l.stach@pengutronix.de; lpieralisi@kernel.org;
> kwilczynski@kernel.org; robh@kernel.org; bhelgaas@google.com;
> s.hauer@pengutronix.de; kernel@pengutronix.de; festevam@gmail.com; linux-
> pci@vger.kernel.org; linux-arm-kernel@lists.infradead.org; imx@lists.linux.dev;
> linux-kernel@vger.kernel.org; Hongxing Zhu <hongxing.zhu@nxp.com>
> Subject: Re: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with
> RC power loss
> 
> On Thu, Jul 30, 2026 at 07:09:13AM -0500, Bjorn Helgaas wrote:
> > On Thu, Jul 30, 2026 at 08:16:36AM +0000, Hongxing Zhu (OSS) wrote:
> > > > -----Original Message-----
> > > > From: Bjorn Helgaas <helgaas@kernel.org>
> > > > Sent: Thursday, July 30, 2026 6:30 AM
> > > ...
> >
> > > > On Fri, Jul 17, 2026 at 03:41:21PM +0800, hongxing.zhu@oss.nxp.com
> wrote:
> > > > > From: Richard Zhu <hongxing.zhu@nxp.com>
> > > > >
> > > > > Some platforms like i.MX power off their PCIe RC controllers
> > > > > during system suspend, requiring full re-initialization on
> > > > > resume. These platforms need to enter L2 state to properly
> > > > > notify endpoints before power loss.
> > > > >
> > > > > According to PCIe base spec r7.0, sec 5.2, the system software
> > > > > should transition the device into D3Hot before broadcasting the
> > > > > PME_Turn_Off message to initiate L2 entry. However, some
> > > > > endpoint devices fail the D3cold capability check in
> > > > > pci_host_common_d3cold_possible(), which would normally prevent L2
> entry.
> > > >
> > > > Wakeup devices that don't support PME from D3cold will fail the
> > > > D3cold capability check, but I don't think those are the problem
> > > > you're solving.
> > > >
> > > You're right.
> > >
> > > > This appears to handle devices that are not in D3hot, and that's
> > > > not a property of the endpoint; it's a property of its driver.  Is
> > > > the problem here that some driver didn't put its device in D3hot?
> > > >
> > > I observed some endpoint devices failing the D3cold capability
> > > check, but I haven't identified the root cause.
> >
> > Seems like some instrumentation in pci_host_common_d3cold_possible()
> > could tell us which devices/drivers are relevant.
> >
> > > > > For platforms where the RC loses power during suspend, L2 entry
> > > > > is essential regardless of D3cold support, as the link will be
> > > > > lost anyway.  Add a suspend_poweroff flag to force L2 entry in
> > > > > such cases, and enable it for i.MX PCIe controllers.
> > > > >
> > > > > Note: This violates the spec requirement that devices be in
> > > > > D3Hot before PME_Turn_Off, but is necessary for proper operation
> > > > > on platforms with RC power loss during suspend.
> > > >
> > > > If the device isn't in D3hot, it may still be active, and I think
> > > > the PME_Turn_Off will abort any DMAs in progress, which doesn't
> > > > sound like proper operation of the endpoint.
> > >
> > > You're correct - this isn't ideal for endpoint operation. However,
> > > on i.MX platforms, the RC controller will lose power during system
> > > suspend regardless. Without sending PME_Turn_Off, endpoints would
> > > have no notification before the link abruptly goes down.
> >
> > The PME_Turn_Off is some notification, but I don't think the endpoint
> > can do DMA or MSI, so its driver won't be involved.  It may be able to
> > do things internally, e.g., write caches to an SSD or transmit packets
> > from its internal buffers.  But I think it might still lose power in
> > the middle of operations like that, so it doesn't sound reliable.
> >
> > > This patch adds a flag to force L2 entry for such platforms,
> > > choosing to notify endpoints (even if not ideal) rather than having
> > > the link drop unexpectedly. I'm appreciated for suggestions if
> > > there's a better approach to handle this scenario.
> >
> > Mani recently added pci_suspend_retains_context(), and I think it
> > returns "true" on i.MX.  But if the RC is powered off and all the
> > devices need full re-initialization on resume, it sounds like it
> > *should* return "false".
> 
> Right. pci_suspend_retains_context() was added just for that purpose of telling
> client drivers to prepare for context loss. So if this API returns 'false', then they
> should not hold the device in D0.
Thanks for your comments.

If I update dw_pcie_suspend_noirq() to use pci_suspend_retains_context() to
determine whether to proceed with L2 entry and RC power down. The new logic
would be changed as below:

-       if (!pci_host_common_d3cold_possible(pci->pp.bridge, &pme_capable))
+       list_for_each_entry(pdev, &bridge->bus->devices, bus_list) {
+               context_retain &= pci_suspend_retains_context(pdev);
+               if (!context_retain)
+                       break;
+       }
+
+       d3cold = pci_host_common_d3cold_possible(bridge, &pme_capable);
+       /*
+        * Enter L2 if:
+        * 1. D3cold is supported (normal case), OR
+        * 2. Any device doesn't retain context during suspend
+        *    (indicates RC power loss, requiring L2 entry to notify
+        *    endpoints via PME_Turn_Off before power is lost)
+        */
+       if (!d3cold && context_retain)
                return 0;

This means:

If context is NOT retained (pci_suspend_retains_context() returns false), the
function will proceed with L2 entry.
If context IS retained (returns true) AND D3cold is not possible, it will skip
suspend operations.
For i.MX: pci_suspend_retains_context() returns false (since i.MX PCIe RC
loses power), the RC will properly enter L2 and power down.

So do Qcom PCIe driver(pci_suspend_retains_context() returns false as well).

Is this approach acceptable for Qcom?

Best Regards
Richard Zhu
> 
> - Mani
> 
> --
> மணிவண்ணன் சதாசிவம்

Re: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[Bjorn Helgaas]

On Tue, Aug 04, 2026 at 06:32:26AM +0000, Hongxing Zhu (OSS) wrote:
> > -----Original Message-----
> > From: Manivannan Sadhasivam <mani@kernel.org>
> > Sent: Monday, August 3, 2026 11:33 PM
> ...

> > On Thu, Jul 30, 2026 at 07:09:13AM -0500, Bjorn Helgaas wrote:
> > > On Thu, Jul 30, 2026 at 08:16:36AM +0000, Hongxing Zhu (OSS) wrote:
> > > > > -----Original Message-----
> > > > > From: Bjorn Helgaas <helgaas@kernel.org>
> > > > > Sent: Thursday, July 30, 2026 6:30 AM
> > > > ...
> > >
> > > > > On Fri, Jul 17, 2026 at 03:41:21PM +0800, hongxing.zhu@oss.nxp.com
> > wrote:
> > > > > > From: Richard Zhu <hongxing.zhu@nxp.com>
> > > > > >
> > > > > > Some platforms like i.MX power off their PCIe RC
> > > > > > controllers during system suspend, requiring full
> > > > > > re-initialization on resume. These platforms need to enter
> > > > > > L2 state to properly notify endpoints before power loss.
> > > > > >
> > > > > > According to PCIe base spec r7.0, sec 5.2, the system
> > > > > > software should transition the device into D3Hot before
> > > > > > broadcasting the PME_Turn_Off message to initiate L2
> > > > > > entry. However, some endpoint devices fail the D3cold
> > > > > > capability check in pci_host_common_d3cold_possible(),
> > > > > > which would normally prevent L2 entry.
> > > > >
> > > > > Wakeup devices that don't support PME from D3cold will fail
> > > > > the D3cold capability check, but I don't think those are the
> > > > > problem you're solving.
> > > > >
> > > > You're right.
> > > >
> > > > > This appears to handle devices that are not in D3hot, and
> > > > > that's not a property of the endpoint; it's a property of
> > > > > its driver.  Is the problem here that some driver didn't put
> > > > > its device in D3hot?
> > > > >
> > > > I observed some endpoint devices failing the D3cold capability
> > > > check, but I haven't identified the root cause.
> > >
> > > Seems like some instrumentation in
> > > pci_host_common_d3cold_possible() could tell us which
> > > devices/drivers are relevant.
> > >
> > > > > > For platforms where the RC loses power during suspend, L2
> > > > > > entry is essential regardless of D3cold support, as the
> > > > > > link will be lost anyway.  Add a suspend_poweroff flag to
> > > > > > force L2 entry in such cases, and enable it for i.MX PCIe
> > > > > > controllers.
> > > > > >
> > > > > > Note: This violates the spec requirement that devices be
> > > > > > in D3Hot before PME_Turn_Off, but is necessary for proper
> > > > > > operation on platforms with RC power loss during suspend.
> > > > >
> > > > > If the device isn't in D3hot, it may still be active, and I
> > > > > think the PME_Turn_Off will abort any DMAs in progress,
> > > > > which doesn't sound like proper operation of the endpoint.
> > > >
> > > > You're correct - this isn't ideal for endpoint operation.
> > > > However, on i.MX platforms, the RC controller will lose power
> > > > during system suspend regardless. Without sending
> > > > PME_Turn_Off, endpoints would have no notification before the
> > > > link abruptly goes down.
> > >
> > > The PME_Turn_Off is some notification, but I don't think the
> > > endpoint can do DMA or MSI, so its driver won't be involved.  It
> > > may be able to do things internally, e.g., write caches to an
> > > SSD or transmit packets from its internal buffers.  But I think
> > > it might still lose power in the middle of operations like that,
> > > so it doesn't sound reliable.
> > >
> > > > This patch adds a flag to force L2 entry for such platforms,
> > > > choosing to notify endpoints (even if not ideal) rather than
> > > > having the link drop unexpectedly. I'm appreciated for
> > > > suggestions if there's a better approach to handle this
> > > > scenario.
> > >
> > > Mani recently added pci_suspend_retains_context(), and I think
> > > it returns "true" on i.MX.  But if the RC is powered off and all
> > > the devices need full re-initialization on resume, it sounds
> > > like it *should* return "false".
> > 
> > Right. pci_suspend_retains_context() was added just for that
> > purpose of telling client drivers to prepare for context loss. So
> > if this API returns 'false', then they should not hold the device
> > in D0.
>
> Thanks for your comments.
> 
> If I update dw_pcie_suspend_noirq() to use
> pci_suspend_retains_context() to determine whether to proceed with
> L2 entry and RC power down. The new logic would be changed as below:

I'm not suggesting using pci_suspend_retains_context() in
dw_pcie_suspend_noirq().  pci_suspend_retains_context() is for
endpoint drivers.

I think pci_suspend_retains_context() should return 'false' on any
platform where dw_pcie_suspend_noirq() is going to send PME_Turn_Off.
Sending PME_Turn_Off means we intend to remove main power.  When main
power is removed, devices will be in D3cold and they will not retain
their internal context.

If pci_suspend_retains_context() returns 'false' and
pci_host_common_d3cold_possible() returns also returns 'false', it
means some driver didn't put its device in D3hot when it should have.

In that case, I think you should either fix that driver so it *does*
put the device in D3hot (based on pci_suspend_retains_context()), or
just accept that you can't power off the RC.

RE: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[Hongxing Zhu (OSS)]

> -----Original Message-----
> From: Bjorn Helgaas <helgaas@kernel.org>
> Sent: Wednesday, August 5, 2026 2:19 AM
> To: Hongxing Zhu (OSS) <hongxing.zhu@oss.nxp.com>
> Cc: Manivannan Sadhasivam <mani@kernel.org>; Frank Li <frank.li@nxp.com>;
> l.stach@pengutronix.de; lpieralisi@kernel.org; kwilczynski@kernel.org;
> robh@kernel.org; bhelgaas@google.com; s.hauer@pengutronix.de;
> kernel@pengutronix.de; festevam@gmail.com; linux-pci@vger.kernel.org; linux-
> arm-kernel@lists.infradead.org; imx@lists.linux.dev; linux-
> kernel@vger.kernel.org; Hongxing Zhu <hongxing.zhu@nxp.com>
> Subject: Re: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with
> RC power loss
> 
> On Tue, Aug 04, 2026 at 06:32:26AM +0000, Hongxing Zhu (OSS) wrote:
> > > -----Original Message-----
> > > From: Manivannan Sadhasivam <mani@kernel.org>
> > > Sent: Monday, August 3, 2026 11:33 PM
> > ...
> 
> > > On Thu, Jul 30, 2026 at 07:09:13AM -0500, Bjorn Helgaas wrote:
> > > > On Thu, Jul 30, 2026 at 08:16:36AM +0000, Hongxing Zhu (OSS) wrote:
> > > > > > -----Original Message-----
> > > > > > From: Bjorn Helgaas <helgaas@kernel.org>
> > > > > > Sent: Thursday, July 30, 2026 6:30 AM
> > > > > ...
> > > >
> > > > > > On Fri, Jul 17, 2026 at 03:41:21PM +0800,
> > > > > > hongxing.zhu@oss.nxp.com
> > > wrote:
> > > > > > > From: Richard Zhu <hongxing.zhu@nxp.com>
> > > > > > >
> > > > > > > Some platforms like i.MX power off their PCIe RC controllers
> > > > > > > during system suspend, requiring full re-initialization on
> > > > > > > resume. These platforms need to enter
> > > > > > > L2 state to properly notify endpoints before power loss.
> > > > > > >
> > > > > > > According to PCIe base spec r7.0, sec 5.2, the system
> > > > > > > software should transition the device into D3Hot before
> > > > > > > broadcasting the PME_Turn_Off message to initiate L2 entry.
> > > > > > > However, some endpoint devices fail the D3cold capability
> > > > > > > check in pci_host_common_d3cold_possible(),
> > > > > > > which would normally prevent L2 entry.
> > > > > >
> > > > > > Wakeup devices that don't support PME from D3cold will fail
> > > > > > the D3cold capability check, but I don't think those are the
> > > > > > problem you're solving.
> > > > > >
> > > > > You're right.
> > > > >
> > > > > > This appears to handle devices that are not in D3hot, and
> > > > > > that's not a property of the endpoint; it's a property of its
> > > > > > driver.  Is the problem here that some driver didn't put its
> > > > > > device in D3hot?
> > > > > >
> > > > > I observed some endpoint devices failing the D3cold capability
> > > > > check, but I haven't identified the root cause.
> > > >
> > > > Seems like some instrumentation in
> > > > pci_host_common_d3cold_possible() could tell us which
> > > > devices/drivers are relevant.
> > > >
> > > > > > > For platforms where the RC loses power during suspend, L2
> > > > > > > entry is essential regardless of D3cold support, as the link
> > > > > > > will be lost anyway.  Add a suspend_poweroff flag to force
> > > > > > > L2 entry in such cases, and enable it for i.MX PCIe
> > > > > > > controllers.
> > > > > > >
> > > > > > > Note: This violates the spec requirement that devices be in
> > > > > > > D3Hot before PME_Turn_Off, but is necessary for proper
> > > > > > > operation on platforms with RC power loss during suspend.
> > > > > >
> > > > > > If the device isn't in D3hot, it may still be active, and I
> > > > > > think the PME_Turn_Off will abort any DMAs in progress, which
> > > > > > doesn't sound like proper operation of the endpoint.
> > > > >
> > > > > You're correct - this isn't ideal for endpoint operation.
> > > > > However, on i.MX platforms, the RC controller will lose power
> > > > > during system suspend regardless. Without sending PME_Turn_Off,
> > > > > endpoints would have no notification before the link abruptly
> > > > > goes down.
> > > >
> > > > The PME_Turn_Off is some notification, but I don't think the
> > > > endpoint can do DMA or MSI, so its driver won't be involved.  It
> > > > may be able to do things internally, e.g., write caches to an SSD
> > > > or transmit packets from its internal buffers.  But I think it
> > > > might still lose power in the middle of operations like that, so
> > > > it doesn't sound reliable.
> > > >
> > > > > This patch adds a flag to force L2 entry for such platforms,
> > > > > choosing to notify endpoints (even if not ideal) rather than
> > > > > having the link drop unexpectedly. I'm appreciated for
> > > > > suggestions if there's a better approach to handle this
> > > > > scenario.
> > > >
> > > > Mani recently added pci_suspend_retains_context(), and I think it
> > > > returns "true" on i.MX.  But if the RC is powered off and all the
> > > > devices need full re-initialization on resume, it sounds like it
> > > > *should* return "false".
> > >
> > > Right. pci_suspend_retains_context() was added just for that purpose
> > > of telling client drivers to prepare for context loss. So if this
> > > API returns 'false', then they should not hold the device in D0.
> >
> > Thanks for your comments.
> >
> > If I update dw_pcie_suspend_noirq() to use
> > pci_suspend_retains_context() to determine whether to proceed with
> > L2 entry and RC power down. The new logic would be changed as below:
> 
> I'm not suggesting using pci_suspend_retains_context() in
> dw_pcie_suspend_noirq().  pci_suspend_retains_context() is for endpoint
> drivers.
> 
> I think pci_suspend_retains_context() should return 'false' on any platform
> where dw_pcie_suspend_noirq() is going to send PME_Turn_Off.
> Sending PME_Turn_Off means we intend to remove main power.  When main
> power is removed, devices will be in D3cold and they will not retain their
> internal context.
> 
> If pci_suspend_retains_context() returns 'false' and
> pci_host_common_d3cold_possible() returns also returns 'false', it means some
> driver didn't put its device in D3hot when it should have.
> 
> In that case, I think you should either fix that driver so it *does* put the device
> in D3hot (based on pci_suspend_retains_context()), or just accept that you can't
> power off the RC.
Understood, thanks for your explanation.

Best Regards
Richard Zhu