From: Thomas Gleixner <tglx@linutronix.de>

Leverage the interrupt redirection infrastructure to enable CPU affinity
support for MSI interrupts. Since the parent interrupt affinity cannot
be changed, affinity control for the child interrupt (MSI) is achieved
by redirecting the handler to run in IRQ work context on the target CPU.

This patch was originally prepared by Thomas Gleixner (see Link tag
below) in a patch series that was never submitted as is, and only
parts of that series have made it upstream so far.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/linux-pci/878qpg4o4t.ffs@tglx/
Co-developed-by: Radu Rendec <rrendec@redhat.com>
Signed-off-by: Radu Rendec <rrendec@redhat.com>
---
 .../pci/controller/dwc/pcie-designware-host.c | 27 +++++++++++++++----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 3ee6a464726ec..a3d4b423a2ab9 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -24,9 +24,21 @@
 static struct pci_ops dw_pcie_ops;
 static struct pci_ops dw_child_pcie_ops;
 
+static void dw_pcie_msi_ack(struct irq_data *d) { }
+
+static bool dw_pcie_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
+				      struct irq_domain *real_parent, struct msi_domain_info *info)
+{
+	if (!msi_lib_init_dev_msi_info(dev, domain, real_parent, info))
+		return false;
+
+	info->chip->irq_ack = dw_pcie_msi_ack;
+	info->chip->irq_pre_redirect = irq_chip_pre_redirect_parent;
+	return true;
+}
+
 #define DW_PCIE_MSI_FLAGS_REQUIRED (MSI_FLAG_USE_DEF_DOM_OPS		| \
 				    MSI_FLAG_USE_DEF_CHIP_OPS		| \
-				    MSI_FLAG_NO_AFFINITY		| \
 				    MSI_FLAG_PCI_MSI_MASK_PARENT)
 #define DW_PCIE_MSI_FLAGS_SUPPORTED (MSI_FLAG_MULTI_PCI_MSI		| \
 				     MSI_FLAG_PCI_MSIX			| \
@@ -36,9 +48,8 @@ static const struct msi_parent_ops dw_pcie_msi_parent_ops = {
 	.required_flags		= DW_PCIE_MSI_FLAGS_REQUIRED,
 	.supported_flags	= DW_PCIE_MSI_FLAGS_SUPPORTED,
 	.bus_select_token	= DOMAIN_BUS_PCI_MSI,
-	.chip_flags		= MSI_CHIP_FLAG_SET_ACK,
 	.prefix			= "DW-",
-	.init_dev_msi_info	= msi_lib_init_dev_msi_info,
+	.init_dev_msi_info	= dw_pcie_init_dev_msi_info,
 };
 
 /* MSI int handler */
@@ -59,7 +70,7 @@ void dw_handle_msi_irq(struct dw_pcie_rp *pp)
 			continue;
 
 		for_each_set_bit(pos, &status, MAX_MSI_IRQS_PER_CTRL)
-			generic_handle_domain_irq(pp->irq_domain, irq_off + pos);
+			generic_handle_demux_domain_irq(pp->irq_domain, irq_off + pos);
 	}
 }
 
@@ -121,7 +132,9 @@ static void dw_pci_bottom_unmask(struct irq_data *d)
 	dw_pcie_writel_dbi(pci, PCIE_MSI_INTR0_MASK + res, pp->irq_mask[ctrl]);
 }
 
-static void dw_pci_bottom_ack(struct irq_data *d)
+static void dw_pci_bottom_ack(struct irq_data *d) { }
+
+static void dw_pci_pre_redirect(struct irq_data *d)
 {
 	struct dw_pcie_rp *pp  = irq_data_get_irq_chip_data(d);
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
@@ -140,6 +153,10 @@ static struct irq_chip dw_pci_msi_bottom_irq_chip = {
 	.irq_compose_msi_msg	= dw_pci_setup_msi_msg,
 	.irq_mask		= dw_pci_bottom_mask,
 	.irq_unmask		= dw_pci_bottom_unmask,
+#ifdef CONFIG_SMP
+	.irq_pre_redirect	= dw_pci_pre_redirect,
+	.irq_set_affinity	= irq_chip_redirect_set_affinity,
+#endif
 };
 
 static int dw_pcie_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
-- 
2.51.0

Hi Radu,

kernel test robot noticed the following build errors:

[auto build test ERROR on tip/irq/core]
[also build test ERROR on pci/next pci/for-linus mani-mhi/mhi-next linus/master v6.17 next-20251003]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Radu-Rendec/genirq-Add-interrupt-redirection-infrastructure/20251004-000948
base:   tip/irq/core
patch link:    https://lore.kernel.org/r/20251003160421.951448-4-rrendec%40redhat.com
patch subject: [PATCH 3/3] PCI: dwc: Enable MSI affinity support
config: x86_64-randconfig-002-20251004 (https://download.01.org/0day-ci/archive/20251004/202510041550.xoRbz92p-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251004/202510041550.xoRbz92p-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202510041550.xoRbz92p-lkp@intel.com/

All errors (new ones prefixed by >>):

   ld: vmlinux.o: in function `dw_pcie_init_dev_msi_info':
>> drivers/pci/controller/dwc/pcie-designware-host.c:36:(.text+0x21dd630): undefined reference to `irq_chip_pre_redirect_parent'


vim +36 drivers/pci/controller/dwc/pcie-designware-host.c

    28	
    29	static bool dw_pcie_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
    30					      struct irq_domain *real_parent, struct msi_domain_info *info)
    31	{
    32		if (!msi_lib_init_dev_msi_info(dev, domain, real_parent, info))
    33			return false;
    34	
    35		info->chip->irq_ack = dw_pcie_msi_ack;
  > 36		info->chip->irq_pre_redirect = irq_chip_pre_redirect_parent;
    37		return true;
    38	}
    39	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Hi Radu,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tip/irq/core]
[also build test WARNING on pci/next pci/for-linus mani-mhi/mhi-next linus/master v6.17 next-20251003]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Radu-Rendec/genirq-Add-interrupt-redirection-infrastructure/20251004-000948
base:   tip/irq/core
patch link:    https://lore.kernel.org/r/20251003160421.951448-4-rrendec%40redhat.com
patch subject: [PATCH 3/3] PCI: dwc: Enable MSI affinity support
config: i386-randconfig-002-20251004 (https://download.01.org/0day-ci/archive/20251004/202510041241.KgbWC5KM-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251004/202510041241.KgbWC5KM-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202510041241.KgbWC5KM-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/pci/controller/dwc/pcie-designware-host.c:137:13: warning: 'dw_pci_pre_redirect' defined but not used [-Wunused-function]
     137 | static void dw_pci_pre_redirect(struct irq_data *d)
         |             ^~~~~~~~~~~~~~~~~~~


vim +/dw_pci_pre_redirect +137 drivers/pci/controller/dwc/pcie-designware-host.c

   136	
 > 137	static void dw_pci_pre_redirect(struct irq_data *d)
   138	{
   139		struct dw_pcie_rp *pp  = irq_data_get_irq_chip_data(d);
   140		struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
   141		unsigned int res, bit, ctrl;
   142	
   143		ctrl = d->hwirq / MAX_MSI_IRQS_PER_CTRL;
   144		res = ctrl * MSI_REG_CTRL_BLOCK_SIZE;
   145		bit = d->hwirq % MAX_MSI_IRQS_PER_CTRL;
   146	
   147		dw_pcie_writel_dbi(pci, PCIE_MSI_INTR0_STATUS + res, BIT(bit));
   148	}
   149	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki