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[PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary_bus()

Manivannan Sadhasivam posted 2 patches 6 months, 4 weeks ago
[PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary_bus()
Posted by Manivannan Sadhasivam 6 months, 4 weeks ago 
host_bridge::reset_slot() is supposed to reset the PCI root port/slot. Once
that happens, the config space content would be lost. This was reported by
Niklas on the dw-rockchip based platform where the MPS setting of the root
port was lost after the host_bridge::reset_slot() callback. Hence, save the
config space before calling the host_bridge::reset_slot() callback and
restore it afterwards.

While at it, make sure that the callback is only called for root ports by
checking if the bridge is behind the root bus.

Fixes: d5c1e1c25b37 ("PCI/ERR: Add support for resetting the slots in a platform specific way")
Reported-by: Niklas Cassel <cassel@kernel.org>
Closes: https://lore.kernel.org/linux-pci/aC9OrPAfpzB_A4K2@ryzen
Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
---
 drivers/pci/pci.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 4d396bbab4a8..6d6e9ce2bbcc 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4985,10 +4985,19 @@ void __weak pcibios_reset_secondary_bus(struct pci_dev *dev)
 	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
 	int ret;
 
-	if (host->reset_slot) {
+	if (pci_is_root_bus(dev->bus) && host->reset_slot) {
+		/*
+		 * Save the config space of the root port before doing the
+		 * reset, since the state could be lost. The device state
+		 * should've been saved by the caller.
+		 */
+		pci_save_state(dev);
 		ret = host->reset_slot(host, dev);
 		if (ret)
 			pci_err(dev, "failed to reset slot: %d\n", ret);
+		else
+			/* Now restore it on success */
+			pci_restore_state(dev);
 
 		return;
 	}
-- 
2.43.0
Re: [PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary_bus()
Posted by Lukas Wunner 6 months, 4 weeks ago 
On Sun, May 25, 2025 at 12:23:03AM +0530, Manivannan Sadhasivam wrote:
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4985,10 +4985,19 @@ void __weak pcibios_reset_secondary_bus(struct pci_dev *dev)
>  	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
>  	int ret;
>  
> -	if (host->reset_slot) {
> +	if (pci_is_root_bus(dev->bus) && host->reset_slot) {
> +		/*
> +		 * Save the config space of the root port before doing the
> +		 * reset, since the state could be lost. The device state
> +		 * should've been saved by the caller.
> +		 */
> +		pci_save_state(dev);
>  		ret = host->reset_slot(host, dev);

Nit:  Capitalize terms as the PCIe Base Spec does, i.e. "Root Port".

"The device state" is ambiguous as the Root Port is a device itself
and even referred to by the "dev" variable.  I think what you mean
is "The Endpoint state".

Thanks,

Lukas
Re: [PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary_bus()
Posted by Manivannan Sadhasivam 6 months, 4 weeks ago 
On Sun, May 25, 2025 at 09:22:03AM +0200, Lukas Wunner wrote:
> On Sun, May 25, 2025 at 12:23:03AM +0530, Manivannan Sadhasivam wrote:
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -4985,10 +4985,19 @@ void __weak pcibios_reset_secondary_bus(struct pci_dev *dev)
> >  	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
> >  	int ret;
> >  
> > -	if (host->reset_slot) {
> > +	if (pci_is_root_bus(dev->bus) && host->reset_slot) {
> > +		/*
> > +		 * Save the config space of the root port before doing the
> > +		 * reset, since the state could be lost. The device state
> > +		 * should've been saved by the caller.
> > +		 */
> > +		pci_save_state(dev);
> >  		ret = host->reset_slot(host, dev);
> 
> Nit:  Capitalize terms as the PCIe Base Spec does, i.e. "Root Port".
> 

Ack.

> "The device state" is ambiguous as the Root Port is a device itself
> and even referred to by the "dev" variable.  I think what you mean
> is "The Endpoint state".
> 

Yes! Will fix them while applying, thanks!

- Mani

-- 
மணிவண்ணன் சதாசிவம்
Re: [PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary_bus()
Posted by Lukas Wunner 6 months, 3 weeks ago 
On Sun, May 25, 2025 at 01:28:18PM +0530, Manivannan Sadhasivam wrote:
> On Sun, May 25, 2025 at 09:22:03AM +0200, Lukas Wunner wrote:
> > "The device state" is ambiguous as the Root Port is a device itself
> > and even referred to by the "dev" variable.  I think what you mean
> > is "The Endpoint state".
> > 
> 
> Yes! Will fix them while applying, thanks!

ICYMI, current controller/dw-rockchip branch still uses
"The device state", not "The Endpoint state" in commit
56eecfc8f46f ("PCI/ERR: Add support for resetting the
Root Ports in a platform specific way").

Otherwise LGTM.

Thanks,

Lukas
Re: [PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary_bus()
Posted by Manivannan Sadhasivam 6 months, 3 weeks ago 
On Mon, May 26, 2025 at 08:54:37AM +0200, Lukas Wunner wrote:
> On Sun, May 25, 2025 at 01:28:18PM +0530, Manivannan Sadhasivam wrote:
> > On Sun, May 25, 2025 at 09:22:03AM +0200, Lukas Wunner wrote:
> > > "The device state" is ambiguous as the Root Port is a device itself
> > > and even referred to by the "dev" variable.  I think what you mean
> > > is "The Endpoint state".
> > > 
> > 
> > Yes! Will fix them while applying, thanks!
> 
> ICYMI, current controller/dw-rockchip branch still uses
> "The device state", not "The Endpoint state" in commit
> 56eecfc8f46f ("PCI/ERR: Add support for resetting the
> Root Ports in a platform specific way").
> 

Ah, missed this comment. Incorported now!

- Mani

-- 
மணிவண்ணன் சதாசிவம்
Re: [PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary_bus()
Posted by Wilfred Mallawa 6 months, 4 weeks ago 
On Sun, 2025-05-25 at 00:23 +0530, Manivannan Sadhasivam wrote:
> host_bridge::reset_slot() is supposed to reset the PCI root
> port/slot. Once
> that happens, the config space content would be lost. This was
> reported by
> Niklas on the dw-rockchip based platform where the MPS setting of the
> root
> port was lost after the host_bridge::reset_slot() callback. Hence,
> save the
> config space before calling the host_bridge::reset_slot() callback
> and
> restore it afterwards.
> 
> While at it, make sure that the callback is only called for root
> ports by
> checking if the bridge is behind the root bus.
> 
> Fixes: d5c1e1c25b37 ("PCI/ERR: Add support for resetting the slots in
> a platform specific way")
> Reported-by: Niklas Cassel <cassel@kernel.org>
> Closes: https://lore.kernel.org/linux-pci/aC9OrPAfpzB_A4K2@ryzen
> Suggested-by: Lukas Wunner <lukas@wunner.de>
> Signed-off-by: Manivannan Sadhasivam
> <manivannan.sadhasivam@linaro.org>
> ---
>  drivers/pci/pci.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 4d396bbab4a8..6d6e9ce2bbcc 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4985,10 +4985,19 @@ void __weak
> pcibios_reset_secondary_bus(struct pci_dev *dev)
>  	struct pci_host_bridge *host = pci_find_host_bridge(dev-
> >bus);
>  	int ret;
>  
> -	if (host->reset_slot) {
> +	if (pci_is_root_bus(dev->bus) && host->reset_slot) {
> +		/*
> +		 * Save the config space of the root port before
> doing the
> +		 * reset, since the state could be lost. The device
> state
> +		 * should've been saved by the caller.
> +		 */
> +		pci_save_state(dev);
>  		ret = host->reset_slot(host, dev);
>  		if (ret)
>  			pci_err(dev, "failed to reset slot: %d\n",
> ret);
> +		else
> +			/* Now restore it on success */
> +			pci_restore_state(dev);
>  
>  		return;
>  	}
Reviewed-by: Wilfred Mallawa <wilfred.mallawa@wdc.com>
Re: [PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary_bus()
Posted by Niklas Cassel 6 months, 4 weeks ago 
On Sun, May 25, 2025 at 12:23:03AM +0530, Manivannan Sadhasivam wrote:
> host_bridge::reset_slot() is supposed to reset the PCI root port/slot. Once
> that happens, the config space content would be lost. This was reported by
> Niklas on the dw-rockchip based platform where the MPS setting of the root
> port was lost after the host_bridge::reset_slot() callback. Hence, save the
> config space before calling the host_bridge::reset_slot() callback and
> restore it afterwards.
> 
> While at it, make sure that the callback is only called for root ports by
> checking if the bridge is behind the root bus.
> 
> Fixes: d5c1e1c25b37 ("PCI/ERR: Add support for resetting the slots in a platform specific way")
> Reported-by: Niklas Cassel <cassel@kernel.org>
> Closes: https://lore.kernel.org/linux-pci/aC9OrPAfpzB_A4K2@ryzen
> Suggested-by: Lukas Wunner <lukas@wunner.de>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
>  drivers/pci/pci.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 4d396bbab4a8..6d6e9ce2bbcc 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4985,10 +4985,19 @@ void __weak pcibios_reset_secondary_bus(struct pci_dev *dev)
>  	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
>  	int ret;
>  
> -	if (host->reset_slot) {
> +	if (pci_is_root_bus(dev->bus) && host->reset_slot) {
> +		/*
> +		 * Save the config space of the root port before doing the
> +		 * reset, since the state could be lost. The device state
> +		 * should've been saved by the caller.
> +		 */
> +		pci_save_state(dev);
>  		ret = host->reset_slot(host, dev);
>  		if (ret)
>  			pci_err(dev, "failed to reset slot: %d\n", ret);
> +		else
> +			/* Now restore it on success */
> +			pci_restore_state(dev);
>  
>  		return;
>  	}
> -- 
> 2.43.0
> 

Looks good to me:
Reviewed-by: Niklas Cassel <cassel@kernel.org>

Patchew 2.1-devel-b67e4c2

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