[bug report] powerpc: per device MSI irq domain

[Nilay Shroff]

Hi Nam,

A gentle ping on this one...

I just rebased to the latest kernel and found that this patch is not 
yet made to the upstream. So may I ask you to submit this change now 
formally to the upstream?

Thanks,
--Nilay

On 12/8/25 5:33 PM, Nilay Shroff wrote:
> 
> 
> On 12/6/25 8:08 PM, Nam Cao wrote:
>> Nilay Shroff <nilay at linux.ibm.com> writes:
>>> Yes you can find the architecture document here: 
>>> https://github.com/linuxppc/public-docs/blob/main/LoPAPR/LoPAR-20200812.pdf
>>>
>>> You may refer section 7 in the above document, which describes RTAS API.
>>
>> Thank you, that helped a lot.
>>
>> Can you please confirm that the below diff fixes the problem? It brings
>> back the "fallback" thing that you mentioned.
>>
>> Best regards,
>> Nam
>>
>> diff --git a/arch/powerpc/platforms/pseries/msi.c b/arch/powerpc/platforms/pseries/msi.c
>> index a82aaa786e9e..8898a968a59b 100644
>> --- a/arch/powerpc/platforms/pseries/msi.c
>> +++ b/arch/powerpc/platforms/pseries/msi.c
>> @@ -19,6 +19,11 @@
>>  
>>  #include "pseries.h"
>>  
>> +struct pseries_msi_device {
>> +	unsigned int msi_quota;
>> +	unsigned int msi_used;
>> +};
>> +
>>  static int query_token, change_token;
>>  
>>  #define RTAS_QUERY_FN		0
>> @@ -433,8 +438,26 @@ static int pseries_msi_ops_prepare(struct irq_domain *domain, struct device *dev
>>  	struct msi_domain_info *info = domain->host_data;
>>  	struct pci_dev *pdev = to_pci_dev(dev);
>>  	int type = (info->flags & MSI_FLAG_PCI_MSIX) ? PCI_CAP_ID_MSIX : PCI_CAP_ID_MSI;
>> +	int ret;
>> +
>> +	struct pseries_msi_device *pseries_dev __free(kfree)
>> +		= kmalloc(sizeof(*pseries_dev), GFP_KERNEL);
>> +	if (!pseries_dev)
>> +		return -ENOMEM;
>> +
>> +	ret = rtas_prepare_msi_irqs(pdev, nvec, type, arg);
>> +	if (ret > 0) {
>> +		nvec = ret;
>> +		ret = rtas_prepare_msi_irqs(pdev, nvec, type, arg);
>> +	}
>> +	if (ret < 0)
>> +		return ret;
>>  
>> -	return rtas_prepare_msi_irqs(pdev, nvec, type, arg);
>> +	pseries_dev->msi_quota = nvec;
>> +	pseries_dev->msi_used = 0;
>> +
>> +	arg->scratchpad[0].ptr = no_free_ptr(pseries_dev);
>> +	return 0;
>>  }
>>  
>>  /*
>> @@ -443,9 +466,13 @@ static int pseries_msi_ops_prepare(struct irq_domain *domain, struct device *dev
>>   */
>>  static void pseries_msi_ops_teardown(struct irq_domain *domain, msi_alloc_info_t *arg)
>>  {
>> +	struct pseries_msi_device *pseries_dev = arg->scratchpad[0].ptr;
>>  	struct pci_dev *pdev = to_pci_dev(domain->dev);
>>  
>>  	rtas_disable_msi(pdev);
>> +
>> +	WARN_ON(pseries_dev->msi_used);
>> +	kfree(pseries_dev);
>>  }
>>  
>>  static void pseries_msi_shutdown(struct irq_data *d)
>> @@ -546,12 +573,18 @@ static int pseries_irq_domain_alloc(struct irq_domain *domain, unsigned int virq
>>  				    unsigned int nr_irqs, void *arg)
>>  {
>>  	struct pci_controller *phb = domain->host_data;
>> +	struct pseries_msi_device *pseries_dev;
>>  	msi_alloc_info_t *info = arg;
>>  	struct msi_desc *desc = info->desc;
>>  	struct pci_dev *pdev = msi_desc_to_pci_dev(desc);
>>  	int hwirq;
>>  	int i, ret;
>>  
>> +	pseries_dev = info->scratchpad[0].ptr;
>> +
>> +	if (pseries_dev->msi_used + nr_irqs > pseries_dev->msi_quota)
>> +		return -ENOSPC;
>> +
>>  	hwirq = rtas_query_irq_number(pci_get_pdn(pdev), desc->msi_index);
>>  	if (hwirq < 0) {
>>  		dev_err(&pdev->dev, "Failed to query HW IRQ: %d\n", hwirq);
>> @@ -567,9 +600,10 @@ static int pseries_irq_domain_alloc(struct irq_domain *domain, unsigned int virq
>>  			goto out;
>>  
>>  		irq_domain_set_hwirq_and_chip(domain, virq + i, hwirq + i,
>> -					      &pseries_msi_irq_chip, domain->host_data);
>> +					      &pseries_msi_irq_chip, pseries_dev);
>>  	}
>>  
>> +	pseries_dev->msi_used++;
>>  	return 0;
>>  
>>  out:
>> @@ -582,9 +616,11 @@ static void pseries_irq_domain_free(struct irq_domain *domain, unsigned int virq
>>  				    unsigned int nr_irqs)
>>  {
>>  	struct irq_data *d = irq_domain_get_irq_data(domain, virq);
>> -	struct pci_controller *phb = irq_data_get_irq_chip_data(d);
>> +	struct pseries_msi_device *pseries_dev = irq_data_get_irq_chip_data(d);
>> +	struct pci_controller *phb = domain->host_data;
>>  
>>  	pr_debug("%s bridge %pOF %d #%d\n", __func__, phb->dn, virq, nr_irqs);
>> +	pseries_dev->msi_used -= nr_irqs;
>>  	irq_domain_free_irqs_parent(domain, virq, nr_irqs);
>>  }
>>  
> 
> Thnaks for the patch! I tested it on my system and I confirmed that
> this patch fixes the bug reported earlier. That said, if you're
> planning to send a formal patch upstream with the above change then
> please feel free to add,
> 
> Acked-by: Nilay Shroff <nilay at inux.ibm.com>