Re: [RFC, v1 0/3] msi support for platform devices

Vikas Gupta
2020-11-13T17:25:10Z

[-- Attachment #1: Type: text/plain, Size: 4041 bytes --]

Hi Eric,

On Fri, Nov 13, 2020 at 12:10 AM Auger Eric <eric.auger@redhat.com> wrote:
>
> Hi Vikas,
>
> On 11/12/20 6:58 PM, Vikas Gupta wrote:
> > This RFC adds support for MSI for platform devices.
> > a) MSI(s) is/are added in addition to the normal interrupts.
> > b) The vendor specific MSI configuration can be done using
> > callbacks which is implemented as msi module.
> > c) Adds a msi handling module for the Broadcom platform devices.
> >
> > Changes from:
> > -------------
> > v0 to v1:
> > i) Removed MSI device flag VFIO_DEVICE_FLAGS_MSI.
> > ii) Add MSI(s) at the end of the irq list of platform IRQs.
> > MSI(s) with first entry of MSI block has count and flag
> > information.
> > IRQ list: Allocation for IRQs + MSIs are allocated as below
> > Example: if there are 'n' IRQs and 'k' MSIs
> > -------------------------------------------------------
> > |IRQ-0|IRQ-1|....|IRQ-n|MSI-0|MSI-1|MSI-2|......|MSI-k|
> > -------------------------------------------------------
> I have not taken time yet to look at your series, but to me you should have
> |IRQ-0|IRQ-1|....|IRQ-n|MSI|MSIX
> then for setting a given MSIX (i) you would select the MSIx index and
> then set start=i count=1.

As per your suggestion, we should have, if there are n-IRQs, k-MSIXs
and m-MSIs, allocation of IRQs should be done as below

|IRQ0|IRQ1|......|IRQ-(n-1)|MSI|MSIX|
| |
|
|MSIX0||MSIX1||MSXI2|....|MSIX-(k-1)|
|MSI0||MSI1||MSI2|....|MSI-(m-1)|
With this implementation user space can know that, at indexes n and
n+1, edge triggered interrupts are present.
We may add an element in vfio_platform_irq itself to allocate MSIs/MSIXs
struct vfio_platform_irq{
.....
.....
struct vfio_platform_irq *block; => this points to the block
allocation for MSIs/MSIXs and all msi/msix are type of IRQs.
};
OR
Another structure can be defined in 'vfio_pci_private.h'
struct vfio_msi_ctx {
struct eventfd_ctx *trigger;
char *name;
};
and
struct vfio_platform_irq {
.....
.....
struct vfio_msi_ctx *block; => this points to the block allocation
for MSIs/MSIXs
};
Which of the above two options sounds OK to you? Please suggest.

> to me individual MSIs are encoded in the subindex and not in the index.
> The index just selects the "type" of interrupt.
>
> For PCI you just have:
> VFIO_PCI_INTX_IRQ_INDEX,
> VFIO_PCI_MSI_IRQ_INDEX, -> MSI index and then you play with
> start/count
> VFIO_PCI_MSIX_IRQ_INDEX,
> VFIO_PCI_ERR_IRQ_INDEX,
> VFIO_PCI_REQ_IRQ_INDEX,
>
> (include/uapi/linux/vfio.h)

In pci case, type of interrupts is fixed so they can be 'indexed' by
these enums but for VFIO platform user space will need to iterate all
(num_irqs) indexes to know at which indexes edge triggered interrupts
are present.

Thanks,
Vikas
>
> Thanks
>
> Eric
> > MSI-0 will have count=k set and flags set accordingly.
> >
> > Vikas Gupta (3):
> > vfio/platform: add support for msi
> > vfio/platform: change cleanup order
> > vfio/platform: add Broadcom msi module
> >
> > drivers/vfio/platform/Kconfig | 1 +
> > drivers/vfio/platform/Makefile | 1 +
> > drivers/vfio/platform/msi/Kconfig | 9 +
> > drivers/vfio/platform/msi/Makefile | 2 +
> > .../vfio/platform/msi/vfio_platform_bcmplt.c | 74 ++++++
> > drivers/vfio/platform/vfio_platform_common.c | 86 ++++++-
> > drivers/vfio/platform/vfio_platform_irq.c | 238 +++++++++++++++++-
> > drivers/vfio/platform/vfio_platform_private.h | 23 ++
> > 8 files changed, 419 insertions(+), 15 deletions(-)
> > create mode 100644 drivers/vfio/platform/msi/Kconfig
> > create mode 100644 drivers/vfio/platform/msi/Makefile
> > create mode 100644 drivers/vfio/platform/msi/vfio_platform_bcmplt.c
> >