[PATCH] powerpc/pasemi: Defer Nemo IRQ initialization

[PATCH] powerpc/pasemi: Defer Nemo IRQ initialization

[chzigotzky]

From: Christian Zigotzky A-EON Open Source <info@xenosoft.de>

Since pas_pci_init() is now called later during boot, the i8259
initialization in pas_init_IRQ() happens too early and accesses
registers that are not yet mapped, preventing the board from booting.

Move the Nemo-specific i8259 initialization to pas_add_bridge(),
after the ISA bridge has been discovered.

Suggested-by: Darren Stevens <darren@stevens-zone.net>
Tested-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Signed-off-by: Christian Zigotzky A-EON Open Source <info@xenosoft.de>
---
 arch/powerpc/platforms/pasemi/pasemi.h |  6 ++++++
 arch/powerpc/platforms/pasemi/pci.c    |  5 +++++
 arch/powerpc/platforms/pasemi/setup.c  | 12 ++++--------
 3 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/platforms/pasemi/pasemi.h b/arch/powerpc/platforms/pasemi/pasemi.h
index 6f6743b8e48d..01bcfa258625 100644
--- a/arch/powerpc/platforms/pasemi/pasemi.h
+++ b/arch/powerpc/platforms/pasemi/pasemi.h
@@ -7,6 +7,12 @@ extern void pas_pci_init(void);
 struct pci_dev;
 extern void pas_pci_dma_dev_setup(struct pci_dev *dev);
 
+#ifdef CONFIG_PPC_PASEMI_NEMO
+void __init nemo_init_IRQ(void);
+#else
+static inline void __init nemo_init_IRQ(void) { }
+#endif
+
 void __iomem *__init pasemi_pci_getcfgaddr(struct pci_dev *dev, int offset);
 
 extern void __init pasemi_map_registers(void);
diff --git a/arch/powerpc/platforms/pasemi/pci.c b/arch/powerpc/platforms/pasemi/pci.c
index 2df955274652..fb53782da7ec 100644
--- a/arch/powerpc/platforms/pasemi/pci.c
+++ b/arch/powerpc/platforms/pasemi/pci.c
@@ -265,6 +265,11 @@ static int __init pas_add_bridge(struct device_node *dev)
 	 */
 	isa_bridge_find_early(hose);
 
+	/*
+	 * ISA bridge is now active, add the i8259 cascade (if needed)
+	 */
+	nemo_init_IRQ();
+
 	return 0;
 }
 
diff --git a/arch/powerpc/platforms/pasemi/setup.c b/arch/powerpc/platforms/pasemi/setup.c
index 45792ecd5dfd..7a961f2a228f 100644
--- a/arch/powerpc/platforms/pasemi/setup.c
+++ b/arch/powerpc/platforms/pasemi/setup.c
@@ -216,10 +216,12 @@ static void sb600_8259_cascade(struct irq_desc *desc)
 	chip->irq_eoi(&desc->irq_data);
 }
 
-static void __init nemo_init_IRQ(struct mpic *mpic)
+void __init nemo_init_IRQ(void)
 {
 	struct device_node *np;
 	int gpio_virq;
+	struct mpic *mpic;
+
 	/* Connect the SB600's legacy i8259 controller */
 	np = of_find_node_by_path("/pxp@0,e0000000");
 	i8259_init(np, 0);
@@ -230,14 +232,10 @@ static void __init nemo_init_IRQ(struct mpic *mpic)
 	irq_set_chained_handler(gpio_virq, sb600_8259_cascade);
 	mpic_unmask_irq(irq_get_irq_data(gpio_virq));
 
+	mpic = irq_get_chip_data(gpio_virq);
 	irq_set_default_domain(mpic->irqhost);
 }
 
-#else
-
-static inline void nemo_init_IRQ(struct mpic *mpic)
-{
-}
 #endif
 
 static __init void pas_init_IRQ(void)
@@ -300,8 +298,6 @@ static __init void pas_init_IRQ(void)
 		mpic_unmask_irq(irq_get_irq_data(nmi_virq));
 	}
 
-	nemo_init_IRQ(mpic);
-
 	of_node_put(mpic_node);
 	of_node_put(root);
 }
-- 
2.43.0

[PATCH] powerpc/pasemi: Defer Nemo IRQ initialization

[Christian Zigotzky]

Hi all,

I have created a new patch. I hope it is OK. It works without any problems.

Thanks,
Christian

On 24/10/26 09:55, chzigotzky@xenosoft.de wrote:
> From: Christian Zigotzky A-EON Open Source <info@xenosoft.de>
>
> Since pas_pci_init() is now called later during boot, the i8259
> initialization in pas_init_IRQ() happens too early and accesses
> registers that are not yet mapped, preventing the board from booting.
>
> Move the Nemo-specific i8259 initialization to pas_add_bridge(),
> after the ISA bridge has been discovered.
>
> Suggested-by: Darren Stevens <darren@stevens-zone.net>
> Tested-by: Christian Zigotzky <chzigotzky@xenosoft.de>
> Signed-off-by: Christian Zigotzky A-EON Open Source <info@xenosoft.de>
> ---
>   arch/powerpc/platforms/pasemi/pasemi.h |  6 ++++++
>   arch/powerpc/platforms/pasemi/pci.c    |  5 +++++
>   arch/powerpc/platforms/pasemi/setup.c  | 12 ++++--------
>   3 files changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pasemi/pasemi.h b/arch/powerpc/platforms/pasemi/pasemi.h
> index 6f6743b8e48d..01bcfa258625 100644
> --- a/arch/powerpc/platforms/pasemi/pasemi.h
> +++ b/arch/powerpc/platforms/pasemi/pasemi.h
> @@ -7,6 +7,12 @@ extern void pas_pci_init(void);
>   struct pci_dev;
>   extern void pas_pci_dma_dev_setup(struct pci_dev *dev);
>   
> +#ifdef CONFIG_PPC_PASEMI_NEMO
> +void __init nemo_init_IRQ(void);
> +#else
> +static inline void __init nemo_init_IRQ(void) { }
> +#endif
> +
>   void __iomem *__init pasemi_pci_getcfgaddr(struct pci_dev *dev, int offset);
>   
>   extern void __init pasemi_map_registers(void);
> diff --git a/arch/powerpc/platforms/pasemi/pci.c b/arch/powerpc/platforms/pasemi/pci.c
> index 2df955274652..fb53782da7ec 100644
> --- a/arch/powerpc/platforms/pasemi/pci.c
> +++ b/arch/powerpc/platforms/pasemi/pci.c
> @@ -265,6 +265,11 @@ static int __init pas_add_bridge(struct device_node *dev)
>   	 */
>   	isa_bridge_find_early(hose);
>   
> +	/*
> +	 * ISA bridge is now active, add the i8259 cascade (if needed)
> +	 */
> +	nemo_init_IRQ();
> +
>   	return 0;
>   }
>   
> diff --git a/arch/powerpc/platforms/pasemi/setup.c b/arch/powerpc/platforms/pasemi/setup.c
> index 45792ecd5dfd..7a961f2a228f 100644
> --- a/arch/powerpc/platforms/pasemi/setup.c
> +++ b/arch/powerpc/platforms/pasemi/setup.c
> @@ -216,10 +216,12 @@ static void sb600_8259_cascade(struct irq_desc *desc)
>   	chip->irq_eoi(&desc->irq_data);
>   }
>   
> -static void __init nemo_init_IRQ(struct mpic *mpic)
> +void __init nemo_init_IRQ(void)
>   {
>   	struct device_node *np;
>   	int gpio_virq;
> +	struct mpic *mpic;
> +
>   	/* Connect the SB600's legacy i8259 controller */
>   	np = of_find_node_by_path("/pxp@0,e0000000");
>   	i8259_init(np, 0);
> @@ -230,14 +232,10 @@ static void __init nemo_init_IRQ(struct mpic *mpic)
>   	irq_set_chained_handler(gpio_virq, sb600_8259_cascade);
>   	mpic_unmask_irq(irq_get_irq_data(gpio_virq));
>   
> +	mpic = irq_get_chip_data(gpio_virq);
>   	irq_set_default_domain(mpic->irqhost);
>   }
>   
> -#else
> -
> -static inline void nemo_init_IRQ(struct mpic *mpic)
> -{
> -}
>   #endif
>   
>   static __init void pas_init_IRQ(void)
> @@ -300,8 +298,6 @@ static __init void pas_init_IRQ(void)
>   		mpic_unmask_irq(irq_get_irq_data(nmi_virq));
>   	}
>   
> -	nemo_init_IRQ(mpic);
> -
>   	of_node_put(mpic_node);
>   	of_node_put(root);
>   }


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[PATCH] powerpc/pasemi: Defer Nemo IRQ initialization

[Christian Zigotzky]

On 10/30/2026 05:21 PM, Ritesh Harjani (IBM) wrote:
 > Let's ask Christian directly :)
 > @Christian - Once we have v2, would you kindly help us test that
 > please?
 >
 > We think the other approach which Narayana suggested might be a better
 > fix for this and it can avoid preempt_enable/disable() dance. However,
 > looks like we may not have the board where we can reproduce this.
 >
 >
 > -ritesh
 >

Hi all,

Is it possible to add the following patch to the kernel?

Link: 
https://lists.ozlabs.org/pipermail/linuxppc-dev/2026-October/305189.html

It is more important for us because the Nemo board can't boot without 
this patch.

Thanks,
Christian

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Re: [PATCH] powerpc/pasemi: Defer Nemo IRQ initialization

[Ritesh Harjani]

chzigotzky@xenosoft.de writes:

> From: Christian Zigotzky A-EON Open Source <info@xenosoft.de>
>
> Since pas_pci_init() is now called later during boot, the i8259
> initialization in pas_init_IRQ() happens too early and accesses
> registers that are not yet mapped, preventing the board from booting.
>
> Move the Nemo-specific i8259 initialization to pas_add_bridge(),
> after the ISA bridge has been discovered.


That make sense to me. The patch looks good. However, shouldn't we also
add Fixes tag and Cc: stable tag - so that this gets backported to older
stable kernels.


Fixes: c144bc719234 ("powerpc/pasemi: Move PHB discovery")
Cc: stable@vger.kernel.org

I think the fixes tag should be above - but feel free to correct that.

Otherwise looks good to me. Feel free to add:
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>


>
> Suggested-by: Darren Stevens <darren@stevens-zone.net>
> Tested-by: Christian Zigotzky <chzigotzky@xenosoft.de>
> Signed-off-by: Christian Zigotzky A-EON Open Source <info@xenosoft.de>
> ---
>  arch/powerpc/platforms/pasemi/pasemi.h |  6 ++++++
>  arch/powerpc/platforms/pasemi/pci.c    |  5 +++++
>  arch/powerpc/platforms/pasemi/setup.c  | 12 ++++--------
>  3 files changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pasemi/pasemi.h b/arch/powerpc/platforms/pasemi/pasemi.h
> index 6f6743b8e48d..01bcfa258625 100644
> --- a/arch/powerpc/platforms/pasemi/pasemi.h
> +++ b/arch/powerpc/platforms/pasemi/pasemi.h
> @@ -7,6 +7,12 @@ extern void pas_pci_init(void);
>  struct pci_dev;
>  extern void pas_pci_dma_dev_setup(struct pci_dev *dev);
>  
> +#ifdef CONFIG_PPC_PASEMI_NEMO
> +void __init nemo_init_IRQ(void);
> +#else
> +static inline void __init nemo_init_IRQ(void) { }
> +#endif
> +
>  void __iomem *__init pasemi_pci_getcfgaddr(struct pci_dev *dev, int offset);
>  
>  extern void __init pasemi_map_registers(void);
> diff --git a/arch/powerpc/platforms/pasemi/pci.c b/arch/powerpc/platforms/pasemi/pci.c
> index 2df955274652..fb53782da7ec 100644
> --- a/arch/powerpc/platforms/pasemi/pci.c
> +++ b/arch/powerpc/platforms/pasemi/pci.c
> @@ -265,6 +265,11 @@ static int __init pas_add_bridge(struct device_node *dev)
>  	 */
>  	isa_bridge_find_early(hose);
>  
> +	/*
> +	 * ISA bridge is now active, add the i8259 cascade (if needed)
> +	 */
> +	nemo_init_IRQ();
> +
>  	return 0;
>  }
>  
> diff --git a/arch/powerpc/platforms/pasemi/setup.c b/arch/powerpc/platforms/pasemi/setup.c
> index 45792ecd5dfd..7a961f2a228f 100644
> --- a/arch/powerpc/platforms/pasemi/setup.c
> +++ b/arch/powerpc/platforms/pasemi/setup.c
> @@ -216,10 +216,12 @@ static void sb600_8259_cascade(struct irq_desc *desc)
>  	chip->irq_eoi(&desc->irq_data);
>  }
>  
> -static void __init nemo_init_IRQ(struct mpic *mpic)
> +void __init nemo_init_IRQ(void)
>  {
>  	struct device_node *np;
>  	int gpio_virq;
> +	struct mpic *mpic;
> +
>  	/* Connect the SB600's legacy i8259 controller */
>  	np = of_find_node_by_path("/pxp@0,e0000000");
>  	i8259_init(np, 0);
> @@ -230,14 +232,10 @@ static void __init nemo_init_IRQ(struct mpic *mpic)
>  	irq_set_chained_handler(gpio_virq, sb600_8259_cascade);
>  	mpic_unmask_irq(irq_get_irq_data(gpio_virq));
>  
> +	mpic = irq_get_chip_data(gpio_virq);
>  	irq_set_default_domain(mpic->irqhost);
>  }
>  
> -#else
> -
> -static inline void nemo_init_IRQ(struct mpic *mpic)
> -{
> -}
>  #endif
>  
>  static __init void pas_init_IRQ(void)
> @@ -300,8 +298,6 @@ static __init void pas_init_IRQ(void)
>  		mpic_unmask_irq(irq_get_irq_data(nmi_virq));
>  	}
>  
> -	nemo_init_IRQ(mpic);
> -
>  	of_node_put(mpic_node);
>  	of_node_put(root);
>  }
> -- 
> 2.43.0

Re: [PATCH] powerpc/pasemi: Defer Nemo IRQ initialization

[Christian Zigotzky]

On 11/02/2026 04:34 AM, Ritesh Harjani (IBM) wrote:
> chzigotzky@xenosoft.de writes:
>
>> From: Christian Zigotzky A-EON Open Source <info@xenosoft.de>
>>
>> Since pas_pci_init() is now called later during boot, the i8259
>> initialization in pas_init_IRQ() happens too early and accesses
>> registers that are not yet mapped, preventing the board from booting.
>>
>> Move the Nemo-specific i8259 initialization to pas_add_bridge(),
>> after the ISA bridge has been discovered.
>
> That make sense to me. The patch looks good. However, shouldn't we also
> add Fixes tag and Cc: stable tag - so that this gets backported to older
> stable kernels.
>
>
> Fixes: c144bc719234 ("powerpc/pasemi: Move PHB discovery")
> Cc: stable@vger.kernel.org
>
> I think the fixes tag should be above - but feel free to correct that.
>
> Otherwise looks good to me. Feel free to add:
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
>
Great! Just for info. I don't need this patch for the stable long-term 
kernel 5.10 but it is at least necessary for the stable long-term 
kernels 6.12 [1] and 6.18.

- Christian

[1] 
https://raw.githubusercontent.com/chzigotzky/kernels/refs/heads/6_12/patches/X1000/pas_pci_init_v6.patch
>> Suggested-by: Darren Stevens <darren@stevens-zone.net>
>> Tested-by: Christian Zigotzky <chzigotzky@xenosoft.de>
>> Signed-off-by: Christian Zigotzky A-EON Open Source <info@xenosoft.de>
>> ---
>>   arch/powerpc/platforms/pasemi/pasemi.h |  6 ++++++
>>   arch/powerpc/platforms/pasemi/pci.c    |  5 +++++
>>   arch/powerpc/platforms/pasemi/setup.c  | 12 ++++--------
>>   3 files changed, 15 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/powerpc/platforms/pasemi/pasemi.h b/arch/powerpc/platforms/pasemi/pasemi.h
>> index 6f6743b8e48d..01bcfa258625 100644
>> --- a/arch/powerpc/platforms/pasemi/pasemi.h
>> +++ b/arch/powerpc/platforms/pasemi/pasemi.h
>> @@ -7,6 +7,12 @@ extern void pas_pci_init(void);
>>   struct pci_dev;
>>   extern void pas_pci_dma_dev_setup(struct pci_dev *dev);
>>   
>> +#ifdef CONFIG_PPC_PASEMI_NEMO
>> +void __init nemo_init_IRQ(void);
>> +#else
>> +static inline void __init nemo_init_IRQ(void) { }
>> +#endif
>> +
>>   void __iomem *__init pasemi_pci_getcfgaddr(struct pci_dev *dev, int offset);
>>   
>>   extern void __init pasemi_map_registers(void);
>> diff --git a/arch/powerpc/platforms/pasemi/pci.c b/arch/powerpc/platforms/pasemi/pci.c
>> index 2df955274652..fb53782da7ec 100644
>> --- a/arch/powerpc/platforms/pasemi/pci.c
>> +++ b/arch/powerpc/platforms/pasemi/pci.c
>> @@ -265,6 +265,11 @@ static int __init pas_add_bridge(struct device_node *dev)
>>   	 */
>>   	isa_bridge_find_early(hose);
>>   
>> +	/*
>> +	 * ISA bridge is now active, add the i8259 cascade (if needed)
>> +	 */
>> +	nemo_init_IRQ();
>> +
>>   	return 0;
>>   }
>>   
>> diff --git a/arch/powerpc/platforms/pasemi/setup.c b/arch/powerpc/platforms/pasemi/setup.c
>> index 45792ecd5dfd..7a961f2a228f 100644
>> --- a/arch/powerpc/platforms/pasemi/setup.c
>> +++ b/arch/powerpc/platforms/pasemi/setup.c
>> @@ -216,10 +216,12 @@ static void sb600_8259_cascade(struct irq_desc *desc)
>>   	chip->irq_eoi(&desc->irq_data);
>>   }
>>   
>> -static void __init nemo_init_IRQ(struct mpic *mpic)
>> +void __init nemo_init_IRQ(void)
>>   {
>>   	struct device_node *np;
>>   	int gpio_virq;
>> +	struct mpic *mpic;
>> +
>>   	/* Connect the SB600's legacy i8259 controller */
>>   	np = of_find_node_by_path("/pxp@0,e0000000");
>>   	i8259_init(np, 0);
>> @@ -230,14 +232,10 @@ static void __init nemo_init_IRQ(struct mpic *mpic)
>>   	irq_set_chained_handler(gpio_virq, sb600_8259_cascade);
>>   	mpic_unmask_irq(irq_get_irq_data(gpio_virq));
>>   
>> +	mpic = irq_get_chip_data(gpio_virq);
>>   	irq_set_default_domain(mpic->irqhost);
>>   }
>>   
>> -#else
>> -
>> -static inline void nemo_init_IRQ(struct mpic *mpic)
>> -{
>> -}
>>   #endif
>>   
>>   static __init void pas_init_IRQ(void)
>> @@ -300,8 +298,6 @@ static __init void pas_init_IRQ(void)
>>   		mpic_unmask_irq(irq_get_irq_data(nmi_virq));
>>   	}
>>   
>> -	nemo_init_IRQ(mpic);
>> -
>>   	of_node_put(mpic_node);
>>   	of_node_put(root);
>>   }
>> -- 
>> 2.43.0


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