Subject: Re: [PATCH v2 1/4] PCI/MSI: Conservatively generalize no_64bit_msi into msi_addr_mask

From: Takashi Iwai <[email-masked]>
Date: Wed, 21 Jan 2026 09:21:44 +0100

On Wed, 21 Jan 2026 04:49:37 +0100,
Vivian Wang wrote:
> 
> Some PCI devices have PCI_MSI_FLAGS_64BIT in the MSI capability, but
> implement less than 64 address bits. This breaks on platforms where such
> a device is assigned an MSI address higher than what's reachable.
> 
> Currently, we deal with this with a single no_64bit_msi flag, and
> (notably on powerpc) forces 32-bit MSI address for these devices.
> However, on some platforms the MSI doorbell address is above 32-bit but
> within device ability.
> 
> As a first step to enabling MSI on those combinations of devices and
> platforms, conservatively generalize the single-bit flag no_64bit_msi
> into msi_addr_mask. (The name msi_addr_mask is chosen to avoid confusion
> with msi_mask.)
> 
> The translation is essentially:
> 
> - no_64bit_msi = 1    ->    msi_addr_mask = DMA_BIT_MASK(32)
> - no_64bit_msi = 0    ->    msi_addr_mask = DMA_BIT_MASK(64)
> - if (no_64bit_msi)   ->    if (msi_addr_mask < DMA_BIT_MASK(64))
> 
> Since no values other than DMA_BIT_MASK(32) and DMA_BIT_MASK(64) is
> used, no functional change is intended. Future patches that make use of
> intermediate values of msi_addr_mask will follow, allowing devices that
> cannot use full 64-bit addresses for MSI to work on platforms with MSI
> doorbell above 32-bit address space.
> 
> Signed-off-by: Vivian Wang <[email-masked]>

For the sound part:

Acked-by: Takashi Iwai <[email-masked]>

thanks,

Takashi

> 
> ---
> 
> v2: Minor rewording. No code changes.
> 
> checkpatch complains about the comment include/linux/pci.h, which I have
> formatted similarly with other comments in the vicinity.
> ---
>  arch/powerpc/platforms/powernv/pci-ioda.c           | 2 +-
>  arch/powerpc/platforms/pseries/msi.c                | 4 ++--
>  drivers/gpu/drm/radeon/radeon_irq_kms.c             | 2 +-
>  drivers/net/ethernet/pensando/ionic/ionic_bus_pci.c | 2 +-
>  drivers/pci/msi/msi.c                               | 2 +-
>  drivers/pci/msi/pcidev_msi.c                        | 2 +-
>  drivers/pci/probe.c                                 | 7 +++++++
>  include/linux/pci.h                                 | 8 +++++++-
>  sound/hda/controllers/intel.c                       | 2 +-
>  9 files changed, 22 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index b0c1d9d16fb5..1c78fdfb7b03 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -1666,7 +1666,7 @@ static int __pnv_pci_ioda_msi_setup(struct pnv_phb *phb, struct pci_dev *dev,
>  		return -ENXIO;
>  
>  	/* Force 32-bit MSI on some broken devices */
> -	if (dev->no_64bit_msi)
> +	if (dev->msi_addr_mask < DMA_BIT_MASK(64))
>  		is_64 = 0;
>  
>  	/* Assign XIVE to PE */
> diff --git a/arch/powerpc/platforms/pseries/msi.c b/arch/powerpc/platforms/pseries/msi.c
> index a82aaa786e9e..7473c7ca1db0 100644
> --- a/arch/powerpc/platforms/pseries/msi.c
> +++ b/arch/powerpc/platforms/pseries/msi.c
> @@ -383,7 +383,7 @@ static int rtas_prepare_msi_irqs(struct pci_dev *pdev, int nvec_in, int type,
>  	 */
>  again:
>  	if (type == PCI_CAP_ID_MSI) {
> -		if (pdev->no_64bit_msi) {
> +		if (pdev->msi_addr_mask < DMA_BIT_MASK(64)) {
>  			rc = rtas_change_msi(pdn, RTAS_CHANGE_32MSI_FN, nvec);
>  			if (rc < 0) {
>  				/*
> @@ -409,7 +409,7 @@ static int rtas_prepare_msi_irqs(struct pci_dev *pdev, int nvec_in, int type,
>  		if (use_32bit_msi_hack && rc > 0)
>  			rtas_hack_32bit_msi_gen2(pdev);
>  	} else {
> -		if (pdev->no_64bit_msi)
> +		if (pdev->msi_addr_mask < DMA_BIT_MASK(64))
>  			rc = rtas_change_msi(pdn, RTAS_CHANGE_32MSIX_FN, nvec);
>  		else
>  			rc = rtas_change_msi(pdn, RTAS_CHANGE_MSIX_FN, nvec);
> diff --git a/drivers/gpu/drm/radeon/radeon_irq_kms.c b/drivers/gpu/drm/radeon/radeon_irq_kms.c
> index 9961251b44ba..d550554a6f3f 100644
> --- a/drivers/gpu/drm/radeon/radeon_irq_kms.c
> +++ b/drivers/gpu/drm/radeon/radeon_irq_kms.c
> @@ -252,7 +252,7 @@ static bool radeon_msi_ok(struct radeon_device *rdev)
>  	 */
>  	if (rdev->family < CHIP_BONAIRE) {
>  		dev_info(rdev->dev, "radeon: MSI limited to 32-bit\n");
> -		rdev->pdev->no_64bit_msi = 1;
> +		rdev->pdev->msi_addr_mask = DMA_BIT_MASK(32);
>  	}
>  
>  	/* force MSI on */
> diff --git a/drivers/net/ethernet/pensando/ionic/ionic_bus_pci.c b/drivers/net/ethernet/pensando/ionic/ionic_bus_pci.c
> index 70d86c5f52fb..0671deae9a28 100644
> --- a/drivers/net/ethernet/pensando/ionic/ionic_bus_pci.c
> +++ b/drivers/net/ethernet/pensando/ionic/ionic_bus_pci.c
> @@ -331,7 +331,7 @@ static int ionic_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>  
>  #ifdef CONFIG_PPC64
>  	/* Ensure MSI/MSI-X interrupts lie within addressable physical memory */
> -	pdev->no_64bit_msi = 1;
> +	pdev->msi_addr_mask = DMA_BIT_MASK(32);
>  #endif
>  
>  	err = ionic_setup_one(ionic);
> diff --git a/drivers/pci/msi/msi.c b/drivers/pci/msi/msi.c
> index 34d664139f48..48f5f03d1479 100644
> --- a/drivers/pci/msi/msi.c
> +++ b/drivers/pci/msi/msi.c
> @@ -322,7 +322,7 @@ static int msi_verify_entries(struct pci_dev *dev)
>  {
>  	struct msi_desc *entry;
>  
> -	if (!dev->no_64bit_msi)
> +	if (dev->msi_addr_mask == DMA_BIT_MASK(64))
>  		return 0;
>  
>  	msi_for_each_desc(entry, &dev->dev, MSI_DESC_ALL) {
> diff --git a/drivers/pci/msi/pcidev_msi.c b/drivers/pci/msi/pcidev_msi.c
> index 5520aff53b56..0b0346813092 100644
> --- a/drivers/pci/msi/pcidev_msi.c
> +++ b/drivers/pci/msi/pcidev_msi.c
> @@ -24,7 +24,7 @@ void pci_msi_init(struct pci_dev *dev)
>  	}
>  
>  	if (!(ctrl & PCI_MSI_FLAGS_64BIT))
> -		dev->no_64bit_msi = 1;
> +		dev->msi_addr_mask = DMA_BIT_MASK(32);
>  }
>  
>  void pci_msix_init(struct pci_dev *dev)
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 41183aed8f5d..a2bff57176a3 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2047,6 +2047,13 @@ int pci_setup_device(struct pci_dev *dev)
>  	 */
>  	dev->dma_mask = 0xffffffff;
>  
> +	/*
> +	 * Assume 64-bit addresses for MSI initially. Will be changed to 32-bit
> +	 * if MSI (rather than MSI-X) capability does not have
> +	 * PCI_MSI_FLAGS_64BIT. Can also be overridden by driver.
> +	 */
> +	dev->msi_addr_mask = DMA_BIT_MASK(64);
> +
>  	dev_set_name(&dev->dev, "%04x:%02x:%02x.%d", pci_domain_nr(dev->bus),
>  		     dev->bus->number, PCI_SLOT(dev->devfn),
>  		     PCI_FUNC(dev->devfn));
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 864775651c6f..0fe32fef0331 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -377,6 +377,13 @@ struct pci_dev {
>  					   0xffffffff.  You only need to change
>  					   this if your device has broken DMA
>  					   or supports 64-bit transfers.  */
> +	u64		msi_addr_mask;	/* Mask of the bits of bus address for
> +					   MSI that this device implements.
> +					   Normally set based on device
> +					   capabilities. You only need to
> +					   change this if your device claims
> +					   to support 64-bit MSI but implements
> +					   fewer than 64 address bits. */
>  
>  	struct device_dma_parameters dma_parms;
>  
> @@ -441,7 +448,6 @@ struct pci_dev {
>  
>  	unsigned int	is_busmaster:1;		/* Is busmaster */
>  	unsigned int	no_msi:1;		/* May not use MSI */
> -	unsigned int	no_64bit_msi:1;		/* May only use 32-bit MSIs */
>  	unsigned int	block_cfg_access:1;	/* Config space access blocked */
>  	unsigned int	broken_parity_status:1;	/* Generates false positive parity */
>  	unsigned int	irq_reroute_variant:2;	/* Needs IRQ rerouting variant */
> diff --git a/sound/hda/controllers/intel.c b/sound/hda/controllers/intel.c
> index 1e8e3d61291a..c9542ebdf7e2 100644
> --- a/sound/hda/controllers/intel.c
> +++ b/sound/hda/controllers/intel.c
> @@ -1905,7 +1905,7 @@ static int azx_first_init(struct azx *chip)
>  
>  	if (chip->msi && chip->driver_caps & AZX_DCAPS_NO_MSI64) {
>  		dev_dbg(card->dev, "Disabling 64bit MSI\n");
> -		pci->no_64bit_msi = true;
> +		pci->msi_addr_mask = DMA_BIT_MASK(32);
>  	}
>  
>  	pci_set_master(pci);
> 
> -- 
> 2.52.0
>