Date:   Wed, 18 Nov 2020 12:00:05 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Vikas Gupta <vikas.gupta@...adcom.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vikram Prakash <vikram.prakash@...adcom.com>,
        Srinath Mannam <srinath.mannam@...adcom.com>,
        Manish Kurup <manish.kurup@...adcom.com>
Subject: Re: [RFC, v1 0/3] msi support for platform devices

Hi Vikas,

On 11/17/20 5:36 PM, Vikas Gupta wrote:
> Hi Eric,
> 
> On Tue, Nov 17, 2020 at 1:55 PM Auger Eric <eric.auger@...hat.com> wrote:
>>
>> Hi Vikas,
>>
>> On 11/17/20 9:05 AM, Auger Eric wrote:
>>> Hi Vikas,
>>>
>>> On 11/17/20 7:25 AM, Vikas Gupta wrote:
>>>> Hi Eric,
>>>>
>>>> On Mon, Nov 16, 2020 at 6:44 PM Auger Eric <eric.auger@...hat.com> wrote:
>>>>>
>>>>> Hi Vikas,
>>>>>
>>>>> On 11/13/20 6:24 PM, Vikas Gupta wrote:
>>>>>> Hi Eric,
>>>>>>
>>>>>> On Fri, Nov 13, 2020 at 12:10 AM Auger Eric <eric.auger@...hat.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)|
>>>>> No I really meant this list of indices: IRQ0|IRQ1|......|IRQ-(n-1)|MSI|MSIX|
>>>>> and potentially later on IRQ0|IRQ1|......|IRQ-(n-1)|MSI|MSIX| ERR| REQ
>>>>> if ERR/REQ were to be added.
>>>> I agree on this. Actually the map I drew incorrectly above but wanted
>>>> to demonstrate the same. It was a child-parent relationship for MSI
>>>> and its members and similarly for MSIX as well.
>>>>>
>>>>> I think the userspace could query the total number of indices using
>>>>> VFIO_DEVICE_GET_INFO and retrieve num_irqs (corresponding to the n wire
>>>>> interrupts + MSI index + MSIX index)
>>>>>
>>>>> Then userspace can loop on all the indices using
>>>>> VFIO_DEVICE_GET_IRQ_INFO. For each index it uses count to determine the
>>>>> first indices related to wire interrupts (count = 1). Then comes the MSI
>>>>> index, and after the MSI index. If any of those is supported, count >1,
>>>>> otherwise count=0. The only thing I am dubious about is can the device
>>>>> use a single MSI/MSIX? Because my hypothesis here is we use count to
>>>>> discriminate between wire first indices and other indices.
>>>> I believe count can be one as well, especially for ERR/REQ as you
>>>> mentioned above.
>>> Given ERR and REQ indices would follow MSI and MSIX ones, MSI index
>>> could be recognized by the first index whose count != 1. But indeed I am
>>> not sure the number of supported vectors cannot be 1. In your case it is
>>> induced by the size of the ring so it is OK but for other devices this
>>> may be different.
>>>
>>> I think we can not rely on the count > 1. Now, this is
>>>> blocking and we are not left with options unless we consider adding
>>>> more enums in flags in vfio_irq_info to tell userspace that particular
>>>> index is wired, MSI, MSIX etc. for the platform device.
>>>> What do you think?
>>> If count is not reliable to discriminate the first n wired interrupts
>>> from the subsequen MSI and MSIx index, Alex suggested to add a
>>> capability extension in the vfio_irq_info structure. Something similar
>>> to what was done for vfio_region_info.
>>>
>>> Such kind of thing was attempted in
>>> https://lore.kernel.org/kvmarm/20201116110030.32335-8-eric.auger@redhat.com/T/#u
>>>
>>> ` [PATCH v11 07/13] vfio: Use capability chains to handle device
>>> specific irq
>>> ` [PATCH v11 08/13] vfio/pci: Add framework for custom interrupt indices
>>> ` [PATCH v11 09/13] vfio: Add new IRQ for DMA fault reporting
>>
>> By the way I was mentionning MSI/MSIx in my previous reply but, as Alex
>> pointed out, with platform device only a single MSI index does make
>> sense, no?
> Yes, I think single MSI should be OK.
> This single MSI index should be implemented as ext_irqs, similar to,
> as you implemented in the mentioned patch. Is my understanding
> correct?
Yes, if count !=1 cannot be used to detect the MSI index, I think using
a capability would do the job and this is aligned with last Alex'
suggestion.

Thanks

Eric
> Thanks,
> Vikas
>>
>> Thanks
>>
>> Eric
>>>
>>> Note this has not been reviewed yet.
>>>
>>> Thanks
>>>
>>> Eric
>>>
>>>>>
>>>>>
>>>>>
>>>>>> With this implementation user space can know that, at indexes n and
>>>>>> n+1, edge triggered interrupts are present.
>>>>> note wired interrupts can also be edge ones.
>>>>>>    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.As wired interrupts and MSI interrupts coexist, I would store in vdev an
>>>>> array of wired interrupts (the existing vdev->irqs) and a new array for
>>>>> MSI(x) as done in the PCI code.
>>>>>
>>>>> vdev->ctx = kcalloc(nvec, sizeof(struct vfio_pci_irq_ctx), GFP_KERNEL);
>>>>>
>>>>> Does it make sense?
>>>> Yes, we can use similar kinds of allocations.
>>>>
>>>> Thanks,
>>>> Vikas
>>>>>
>>>>>>    };
>>>>>>                          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.
>>>>> indeed, but can't you loop over all indices looking until count !=1? At
>>>>> this point you know if have finished emurating the wires. Holds if
>>>>> MSI(x) count !=1 of course.
>>>>>
>>>>> Thanks
>>>>>
>>>>> Eric
>>>>>
>>>>>>
>>>>>> 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
>>>>>>>>
>>>>>>>
>>>>>
>>

Powered by blists - more mailing lists