[PATCH v3] PCI/ASPM: Disable L1 before disabling L1ss

[PATCH v3] PCI/ASPM: Disable L1 before disabling L1ss

[Ajay Agarwal]

The current sequence in the driver for L1ss update is as follows.

Disable L1ss
Disable L1
Enable L1ss as required
Enable L1 if required

With this sequence, a bus hang is observed during the L1ss
disable sequence when the RC CPU attempts to clear the RC L1ss
register after clearing the EP L1ss register. It looks like the
RC attempts to enter L1ss again and at the same time, access to
RC L1ss register fails because aux clk is still not active.

PCIe spec r6.2, section 5.5.4, recommends that setting either
or both of the enable bits for ASPM L1 PM Substates must be done
while ASPM L1 is disabled. My interpretation here is that
clearing L1ss should also be done when L1 is disabled. Thereby,
change the sequence as follows.

Disable L1
Disable L1ss
Enable L1ss as required
Enable L1 if required

Signed-off-by: Ajay Agarwal <ajayagarwal@google.com>
---
Changelog since v2:
 - Add the logic in pcie_aspm_cap_init()

Changelog since v1:
 - Move the L1 disable/enable logic to pcie_config_aspm_link()
 - Add detailed comments including spec version and section number

 drivers/pci/pcie/aspm.c | 66 +++++++++++++++++++++++++----------------
 1 file changed, 40 insertions(+), 26 deletions(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index cee2365e54b8..50997e378631 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -805,6 +805,15 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 	pcie_capability_read_word(parent, PCI_EXP_LNKCTL, &parent_lnkctl);
 	pcie_capability_read_word(child, PCI_EXP_LNKCTL, &child_lnkctl);
 
+	/* Make sure L0s/L1 are disabled before updating L1SS config */
+	if (FIELD_GET(PCI_EXP_LNKCTL_ASPMC, child_lnkctl) ||
+	    FIELD_GET(PCI_EXP_LNKCTL_ASPMC, parent_lnkctl)) {
+		pcie_capability_write_word(child, PCI_EXP_LNKCTL,
+					   child_lnkctl & ~PCI_EXP_LNKCTL_ASPMC);
+		pcie_capability_write_word(parent, PCI_EXP_LNKCTL,
+					   parent_lnkctl & ~PCI_EXP_LNKCTL_ASPMC);
+	}
+
 	/*
 	 * Setup L0s state
 	 *
@@ -829,6 +838,13 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 
 	aspm_l1ss_init(link);
 
+	/* Restore L0s/L1 if they were enabled */
+	if (FIELD_GET(PCI_EXP_LNKCTL_ASPMC, child_lnkctl) ||
+	    FIELD_GET(PCI_EXP_LNKCTL_ASPMC, parent_lnkctl)) {
+		pcie_capability_write_word(parent, PCI_EXP_LNKCTL, parent_lnkctl);
+		pcie_capability_write_word(child, PCI_EXP_LNKCTL, child_lnkctl);
+	}
+
 	/* Save default state */
 	link->aspm_default = link->aspm_enabled;
 
@@ -848,17 +864,13 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 /* Configure the ASPM L1 substates */
 static void pcie_config_aspm_l1ss(struct pcie_link_state *link, u32 state)
 {
-	u32 val, enable_req;
+	u32 val;
 	struct pci_dev *child = link->downstream, *parent = link->pdev;
 
-	enable_req = (link->aspm_enabled ^ state) & state;
-
 	/*
-	 * Here are the rules specified in the PCIe spec for enabling L1SS:
+	 * Spec r6.2, section 5.5.4, mentions the rules for enabling L1SS:
 	 * - When enabling L1.x, enable bit at parent first, then at child
 	 * - When disabling L1.x, disable bit at child first, then at parent
-	 * - When enabling ASPM L1.x, need to disable L1
-	 *   (at child followed by parent).
 	 * - The ASPM/PCIPM L1.2 must be disabled while programming timing
 	 *   parameters
 	 *
@@ -871,16 +883,6 @@ static void pcie_config_aspm_l1ss(struct pcie_link_state *link, u32 state)
 				       PCI_L1SS_CTL1_L1SS_MASK, 0);
 	pci_clear_and_set_config_dword(parent, parent->l1ss + PCI_L1SS_CTL1,
 				       PCI_L1SS_CTL1_L1SS_MASK, 0);
-	/*
-	 * If needed, disable L1, and it gets enabled later
-	 * in pcie_config_aspm_link().
-	 */
-	if (enable_req & (PCIE_LINK_STATE_L1_1 | PCIE_LINK_STATE_L1_2)) {
-		pcie_capability_clear_word(child, PCI_EXP_LNKCTL,
-					   PCI_EXP_LNKCTL_ASPM_L1);
-		pcie_capability_clear_word(parent, PCI_EXP_LNKCTL,
-					   PCI_EXP_LNKCTL_ASPM_L1);
-	}
 
 	val = 0;
 	if (state & PCIE_LINK_STATE_L1_1)
@@ -937,21 +939,33 @@ static void pcie_config_aspm_link(struct pcie_link_state *link, u32 state)
 		dwstream |= PCI_EXP_LNKCTL_ASPM_L1;
 	}
 
+	/*
+	 * Spec r6.2, section 5.5.4, recommends that setting either or both of
+	 * the enable bits for ASPM L1 PM Substates must be done while ASPM L1
+	 * is disabled. So disable L1 here, and it gets enabled later after the
+	 * L1ss configuration has been completed.
+	 *
+	 * Spec r6.2, section 7.5.3.7, mentions that ASPM L1 must be enabled by
+	 * software in the Upstream component on a Link prior to enabling ASPM
+	 * L1 in the Downstream component on the Link. When disabling L1,
+	 * software must disable ASPM L1 in the Downstream component on a Link
+	 * prior to disabling ASPM L1 in the Upstream component on that Link.
+	 *
+	 * Spec doesn't mention L0s.
+	 *
+	 * Disable L1 and L0s here, and they get enabled later after the L1ss
+	 * configuration has been completed.
+	 */
+	list_for_each_entry(child, &linkbus->devices, bus_list)
+		pcie_config_aspm_dev(child, 0);
+	pcie_config_aspm_dev(parent, 0);
+
 	if (link->aspm_capable & PCIE_LINK_STATE_L1SS)
 		pcie_config_aspm_l1ss(link, state);
 
-	/*
-	 * Spec 2.0 suggests all functions should be configured the
-	 * same setting for ASPM. Enabling ASPM L1 should be done in
-	 * upstream component first and then downstream, and vice
-	 * versa for disabling ASPM L1. Spec doesn't mention L0S.
-	 */
-	if (state & PCIE_LINK_STATE_L1)
-		pcie_config_aspm_dev(parent, upstream);
+	pcie_config_aspm_dev(parent, upstream);
 	list_for_each_entry(child, &linkbus->devices, bus_list)
 		pcie_config_aspm_dev(child, dwstream);
-	if (!(state & PCIE_LINK_STATE_L1))
-		pcie_config_aspm_dev(parent, upstream);
 
 	link->aspm_enabled = state;
 
-- 
2.47.0.rc0.187.ge670bccf7e-goog

Re: [PATCH v3] PCI/ASPM: Disable L1 before disabling L1ss

[Ajay Agarwal]

A gentle reminder for review.

Re: [PATCH v3] PCI/ASPM: Disable L1 before disabling L1ss

[Bjorn Helgaas]

On Mon, Oct 07, 2024 at 08:59:17AM +0530, Ajay Agarwal wrote:
> The current sequence in the driver for L1ss update is as follows.
> 
> Disable L1ss
> Disable L1
> Enable L1ss as required
> Enable L1 if required
> 
> With this sequence, a bus hang is observed during the L1ss
> disable sequence when the RC CPU attempts to clear the RC L1ss
> register after clearing the EP L1ss register. It looks like the
> RC attempts to enter L1ss again and at the same time, access to
> RC L1ss register fails because aux clk is still not active.
> 
> PCIe spec r6.2, section 5.5.4, recommends that setting either
> or both of the enable bits for ASPM L1 PM Substates must be done
> while ASPM L1 is disabled. My interpretation here is that
> clearing L1ss should also be done when L1 is disabled. Thereby,
> change the sequence as follows.
> 
> Disable L1
> Disable L1ss
> Enable L1ss as required
> Enable L1 if required
> 
> Signed-off-by: Ajay Agarwal <ajayagarwal@google.com>

Applied to pci/aspm for v6.13, thank you, Ajay!

> ---
> Changelog since v2:
>  - Add the logic in pcie_aspm_cap_init()
> 
> Changelog since v1:
>  - Move the L1 disable/enable logic to pcie_config_aspm_link()
>  - Add detailed comments including spec version and section number
> 
>  drivers/pci/pcie/aspm.c | 66 +++++++++++++++++++++++++----------------
>  1 file changed, 40 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index cee2365e54b8..50997e378631 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -805,6 +805,15 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
>  	pcie_capability_read_word(parent, PCI_EXP_LNKCTL, &parent_lnkctl);
>  	pcie_capability_read_word(child, PCI_EXP_LNKCTL, &child_lnkctl);
>  
> +	/* Make sure L0s/L1 are disabled before updating L1SS config */
> +	if (FIELD_GET(PCI_EXP_LNKCTL_ASPMC, child_lnkctl) ||
> +	    FIELD_GET(PCI_EXP_LNKCTL_ASPMC, parent_lnkctl)) {
> +		pcie_capability_write_word(child, PCI_EXP_LNKCTL,
> +					   child_lnkctl & ~PCI_EXP_LNKCTL_ASPMC);
> +		pcie_capability_write_word(parent, PCI_EXP_LNKCTL,
> +					   parent_lnkctl & ~PCI_EXP_LNKCTL_ASPMC);
> +	}
> +
>  	/*
>  	 * Setup L0s state
>  	 *
> @@ -829,6 +838,13 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
>  
>  	aspm_l1ss_init(link);
>  
> +	/* Restore L0s/L1 if they were enabled */
> +	if (FIELD_GET(PCI_EXP_LNKCTL_ASPMC, child_lnkctl) ||
> +	    FIELD_GET(PCI_EXP_LNKCTL_ASPMC, parent_lnkctl)) {
> +		pcie_capability_write_word(parent, PCI_EXP_LNKCTL, parent_lnkctl);
> +		pcie_capability_write_word(child, PCI_EXP_LNKCTL, child_lnkctl);
> +	}
> +
>  	/* Save default state */
>  	link->aspm_default = link->aspm_enabled;
>  
> @@ -848,17 +864,13 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
>  /* Configure the ASPM L1 substates */
>  static void pcie_config_aspm_l1ss(struct pcie_link_state *link, u32 state)
>  {
> -	u32 val, enable_req;
> +	u32 val;
>  	struct pci_dev *child = link->downstream, *parent = link->pdev;
>  
> -	enable_req = (link->aspm_enabled ^ state) & state;
> -
>  	/*
> -	 * Here are the rules specified in the PCIe spec for enabling L1SS:
> +	 * Spec r6.2, section 5.5.4, mentions the rules for enabling L1SS:
>  	 * - When enabling L1.x, enable bit at parent first, then at child
>  	 * - When disabling L1.x, disable bit at child first, then at parent
> -	 * - When enabling ASPM L1.x, need to disable L1
> -	 *   (at child followed by parent).
>  	 * - The ASPM/PCIPM L1.2 must be disabled while programming timing
>  	 *   parameters
>  	 *
> @@ -871,16 +883,6 @@ static void pcie_config_aspm_l1ss(struct pcie_link_state *link, u32 state)
>  				       PCI_L1SS_CTL1_L1SS_MASK, 0);
>  	pci_clear_and_set_config_dword(parent, parent->l1ss + PCI_L1SS_CTL1,
>  				       PCI_L1SS_CTL1_L1SS_MASK, 0);
> -	/*
> -	 * If needed, disable L1, and it gets enabled later
> -	 * in pcie_config_aspm_link().
> -	 */
> -	if (enable_req & (PCIE_LINK_STATE_L1_1 | PCIE_LINK_STATE_L1_2)) {
> -		pcie_capability_clear_word(child, PCI_EXP_LNKCTL,
> -					   PCI_EXP_LNKCTL_ASPM_L1);
> -		pcie_capability_clear_word(parent, PCI_EXP_LNKCTL,
> -					   PCI_EXP_LNKCTL_ASPM_L1);
> -	}
>  
>  	val = 0;
>  	if (state & PCIE_LINK_STATE_L1_1)
> @@ -937,21 +939,33 @@ static void pcie_config_aspm_link(struct pcie_link_state *link, u32 state)
>  		dwstream |= PCI_EXP_LNKCTL_ASPM_L1;
>  	}
>  
> +	/*
> +	 * Spec r6.2, section 5.5.4, recommends that setting either or both of
> +	 * the enable bits for ASPM L1 PM Substates must be done while ASPM L1
> +	 * is disabled. So disable L1 here, and it gets enabled later after the
> +	 * L1ss configuration has been completed.
> +	 *
> +	 * Spec r6.2, section 7.5.3.7, mentions that ASPM L1 must be enabled by
> +	 * software in the Upstream component on a Link prior to enabling ASPM
> +	 * L1 in the Downstream component on the Link. When disabling L1,
> +	 * software must disable ASPM L1 in the Downstream component on a Link
> +	 * prior to disabling ASPM L1 in the Upstream component on that Link.
> +	 *
> +	 * Spec doesn't mention L0s.
> +	 *
> +	 * Disable L1 and L0s here, and they get enabled later after the L1ss
> +	 * configuration has been completed.
> +	 */
> +	list_for_each_entry(child, &linkbus->devices, bus_list)
> +		pcie_config_aspm_dev(child, 0);
> +	pcie_config_aspm_dev(parent, 0);
> +
>  	if (link->aspm_capable & PCIE_LINK_STATE_L1SS)
>  		pcie_config_aspm_l1ss(link, state);
>  
> -	/*
> -	 * Spec 2.0 suggests all functions should be configured the
> -	 * same setting for ASPM. Enabling ASPM L1 should be done in
> -	 * upstream component first and then downstream, and vice
> -	 * versa for disabling ASPM L1. Spec doesn't mention L0S.
> -	 */
> -	if (state & PCIE_LINK_STATE_L1)
> -		pcie_config_aspm_dev(parent, upstream);
> +	pcie_config_aspm_dev(parent, upstream);
>  	list_for_each_entry(child, &linkbus->devices, bus_list)
>  		pcie_config_aspm_dev(child, dwstream);
> -	if (!(state & PCIE_LINK_STATE_L1))
> -		pcie_config_aspm_dev(parent, upstream);
>  
>  	link->aspm_enabled = state;
>  
> -- 
> 2.47.0.rc0.187.ge670bccf7e-goog
> 

Re: [PATCH v3] PCI/ASPM: Disable L1 before disabling L1ss

[Macpaul Lin (林智斌)]

On Tue, 2024-10-22 at 17:30 -0500, Bjorn Helgaas wrote:
> On Mon, Oct 07, 2024 at 08:59:17AM +0530, Ajay Agarwal wrote:
> > The current sequence in the driver for L1ss update is as follows.
> > 
> > Disable L1ss
> > Disable L1
> > Enable L1ss as required
> > Enable L1 if required
> > 
> > With this sequence, a bus hang is observed during the L1ss
> > disable sequence when the RC CPU attempts to clear the RC L1ss
> > register after clearing the EP L1ss register. It looks like the
> > RC attempts to enter L1ss again and at the same time, access to
> > RC L1ss register fails because aux clk is still not active.
> > 
> > PCIe spec r6.2, section 5.5.4, recommends that setting either
> > or both of the enable bits for ASPM L1 PM Substates must be done
> > while ASPM L1 is disabled. My interpretation here is that
> > clearing L1ss should also be done when L1 is disabled. Thereby,
> > change the sequence as follows.
> > 
> > Disable L1
> > Disable L1ss
> > Enable L1ss as required
> > Enable L1 if required
> > 
> > Signed-off-by: Ajay Agarwal <ajayagarwal@google.com>
> 
> Applied to pci/aspm for v6.13, thank you, Ajay!

Thanks! MediaTek also found this issue will happen on some old kernel,
for example 6.11 or 6.12. would you please pick this patch also to some
stable tree?

LINK:https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/drivers/pci/pcie/aspm.c?id=7447990137bf06b2aeecad9c6081e01a9f47f2aa

Thanks a lot.
Macpaul Lin

Re: [PATCH v3] PCI/ASPM: Disable L1 before disabling L1ss

[Greg KH]

On Thu, Jun 05, 2025 at 11:23:02AM +0000, Macpaul Lin (林智斌) wrote:
> On Tue, 2024-10-22 at 17:30 -0500, Bjorn Helgaas wrote:
> > On Mon, Oct 07, 2024 at 08:59:17AM +0530, Ajay Agarwal wrote:
> > > The current sequence in the driver for L1ss update is as follows.
> > > 
> > > Disable L1ss
> > > Disable L1
> > > Enable L1ss as required
> > > Enable L1 if required
> > > 
> > > With this sequence, a bus hang is observed during the L1ss
> > > disable sequence when the RC CPU attempts to clear the RC L1ss
> > > register after clearing the EP L1ss register. It looks like the
> > > RC attempts to enter L1ss again and at the same time, access to
> > > RC L1ss register fails because aux clk is still not active.
> > > 
> > > PCIe spec r6.2, section 5.5.4, recommends that setting either
> > > or both of the enable bits for ASPM L1 PM Substates must be done
> > > while ASPM L1 is disabled. My interpretation here is that
> > > clearing L1ss should also be done when L1 is disabled. Thereby,
> > > change the sequence as follows.
> > > 
> > > Disable L1
> > > Disable L1ss
> > > Enable L1ss as required
> > > Enable L1 if required
> > > 
> > > Signed-off-by: Ajay Agarwal <ajayagarwal@google.com>
> > 
> > Applied to pci/aspm for v6.13, thank you, Ajay!
> 
> Thanks! MediaTek also found this issue will happen on some old kernel,
> for example 6.11 or 6.12. would you please pick this patch also to some
> stable tree?
> 
> LINK:https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/drivers/pci/pcie/aspm.c?id=7447990137bf06b2aeecad9c6081e01a9f47f2aa

Please submit it properly, with your signed-off-by and we will be glad
to consider it.

thanks,

greg k-h