linux-kernel - Re: [PATCH v2 2/3] PCI: hv: Allow dynamic MSI-X vector allocation

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Message-ID: <20250429084656.GB10839@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Tue, 29 Apr 2025 01:46:56 -0700
From: Shradha Gupta <shradhagupta@...ux.microsoft.com>
To: Michael Kelley <mhklinux@...look.com>
Cc: "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nipun Gupta <nipun.gupta@....com>,
	Yury Norov <yury.norov@...il.com>, Jason Gunthorpe <jgg@...pe.ca>,
	Jonathan Cameron <Jonathan.Cameron@...ei.com>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Kevin Tian <kevin.tian@...el.com>, Long Li <longli@...rosoft.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Rob Herring <robh@...nel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Krzysztof Wilczy?ski <kw@...ux.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Dexuan Cui <decui@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Konstantin Taranov <kotaranov@...rosoft.com>,
	Simon Horman <horms@...nel.org>, Leon Romanovsky <leon@...nel.org>,
	Maxim Levitsky <mlevitsk@...hat.com>,
	Erni Sri Satya Vennela <ernis@...ux.microsoft.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	Paul Rosswurm <paulros@...rosoft.com>,
	Shradha Gupta <shradhagupta@...rosoft.com>
Subject: Re: [PATCH v2 2/3] PCI: hv: Allow dynamic MSI-X vector allocation

On Mon, Apr 28, 2025 at 01:47:22PM +0000, Michael Kelley wrote:
> From: Shradha Gupta <shradhagupta@...ux.microsoft.com> Sent: Friday, April 25, 2025 3:54 AM
> > 
> > Allow dynamic MSI-X vector allocation for pci_hyperv PCI controller
> > by adding support for the flag MSI_FLAG_PCI_MSIX_ALLOC_DYN and using
> > pci_msix_prepare_desc() to prepare the descriptors.
> 
> I'm unclear from the code below whether the intent is to support dynamic
> allocation only x86, or on both x86 and arm64. On arm64, you've defined
> hv_msi_prepare_desc as NULL, but hv_msi_prepare is also defined as NULL
> on arm64, so I'm not sure what to conclude. MSI_FLAG_PCI_MSIX_ALLOC_DYN
> is being set for both architectures.
> 
> In any case, please be explicit about your intent in the commit message.
> If the intent is to not support arm64, why is that?
> 
> Michael

Thank you for the comments Michael, in my recent testing on arm64, turns
out this function is indeed needed for the complete support.
I will test this out more thoroughly on arm64 and include the arm64 support
in next version.

Regards,
Shradha.
> 
> > 
> > Signed-off-by: Shradha Gupta <shradhagupta@...ux.microsoft.com>
> > Reviewed-by: Haiyang Zhang <haiyangz@...rosoft.com>
> > ---
> >  Changes in v2:
> >  * split the patch to keep changes in PCI and pci_hyperv controller
> >    seperate
> >  * replace strings "pci vectors" by "MSI-X vectors"
> > ---
> >  drivers/pci/controller/pci-hyperv.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> > index ac27bda5ba26..f2fa6bdb6bb8 100644
> > --- a/drivers/pci/controller/pci-hyperv.c
> > +++ b/drivers/pci/controller/pci-hyperv.c
> > @@ -598,7 +598,8 @@ static unsigned int hv_msi_get_int_vector(struct irq_data *data)
> >  	return cfg->vector;
> >  }
> > 
> > -#define hv_msi_prepare		pci_msi_prepare
> > +#define hv_msi_prepare			pci_msi_prepare
> > +#define hv_msix_prepare_desc		pci_msix_prepare_desc
> > 
> >  /**
> >   * hv_arch_irq_unmask() - "Unmask" the IRQ by setting its current
> > @@ -727,6 +728,7 @@ static void hv_arch_irq_unmask(struct irq_data *data)
> >  #define FLOW_HANDLER		NULL
> >  #define FLOW_NAME		NULL
> >  #define hv_msi_prepare		NULL
> > +#define hv_msix_prepare_desc	NULL
> > 
> >  struct hv_pci_chip_data {
> >  	DECLARE_BITMAP(spi_map, HV_PCI_MSI_SPI_NR);
> > @@ -2063,6 +2065,7 @@ static struct irq_chip hv_msi_irq_chip = {
> >  static struct msi_domain_ops hv_msi_ops = {
> >  	.msi_prepare	= hv_msi_prepare,
> >  	.msi_free	= hv_msi_free,
> > +	.prepare_desc	= hv_msix_prepare_desc,
> >  };
> > 
> >  /**
> > @@ -2084,7 +2087,7 @@ static int hv_pcie_init_irq_domain(struct hv_pcibus_device *hbus)
> >  	hbus->msi_info.ops = &hv_msi_ops;
> >  	hbus->msi_info.flags = (MSI_FLAG_USE_DEF_DOM_OPS |
> >  		MSI_FLAG_USE_DEF_CHIP_OPS | MSI_FLAG_MULTI_PCI_MSI |
> > -		MSI_FLAG_PCI_MSIX);
> > +		MSI_FLAG_PCI_MSIX | MSI_FLAG_PCI_MSIX_ALLOC_DYN);
> >  	hbus->msi_info.handler = FLOW_HANDLER;
> >  	hbus->msi_info.handler_name = FLOW_NAME;
> >  	hbus->msi_info.data = hbus;
> > --
> > 2.34.1
> >