Message-ID: <20210119154523.00179254@omen.home.shazbot.org>
Date:   Tue, 19 Jan 2021 15:45:23 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     Vikas Gupta <vikas.gupta@...adcom.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>,
        Ashwin Kamath <ashwin.kamath@...adcom.com>,
        Zac Schroff <zachary.schroff@...adcom.com>,
        Manish Kurup <manish.kurup@...adcom.com>
Subject: Re: [RFC v3 2/2] vfio/platform: msi: add Broadcom platform devices

On Fri, 15 Jan 2021 10:24:33 +0100
Auger Eric <eric.auger@...hat.com> wrote:

> Hi Vikas,
> On 1/15/21 7:35 AM, Vikas Gupta wrote:
> > Hi Eric,
> > 
> > On Tue, Jan 12, 2021 at 2:52 PM Auger Eric <eric.auger@...hat.com> wrote:  
> >>
> >> Hi Vikas,
> >>
> >> On 12/14/20 6:45 PM, Vikas Gupta wrote:  
> >>> Add msi support for Broadcom platform devices
> >>>
> >>> Signed-off-by: Vikas Gupta <vikas.gupta@...adcom.com>
> >>> ---
> >>>  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  | 49 +++++++++++++++++++
> >>>  5 files changed, 62 insertions(+)
> >>>  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  
> >> what does plt mean?  
> > This(plt) is a generic name for Broadcom platform devices, which we`ll
> >  plan to add in this file. Currently we have only one in this file.
> > Do you think this name does not sound good here?  
> 
> we have VFIO_PLATFORM_BCMFLEXRM_RESET config which also applied to vfio
> flex-rm platform device.
> 
> I think it would be more homegenous to have VFIO_PLATFORM_BCMFLEXRM_MSI
> in case we keep a separate msi module.
> 
> also in reset dir we have vfio_platform_bcmflexrm.c
> 
> 
> >>>
> >>> diff --git a/drivers/vfio/platform/Kconfig b/drivers/vfio/platform/Kconfig
> >>> index dc1a3c44f2c6..7b8696febe61 100644
> >>> --- a/drivers/vfio/platform/Kconfig
> >>> +++ b/drivers/vfio/platform/Kconfig
> >>> @@ -21,3 +21,4 @@ config VFIO_AMBA
> >>>         If you don't know what to do here, say N.
> >>>
> >>>  source "drivers/vfio/platform/reset/Kconfig"
> >>> +source "drivers/vfio/platform/msi/Kconfig"
> >>> diff --git a/drivers/vfio/platform/Makefile b/drivers/vfio/platform/Makefile
> >>> index 3f3a24e7c4ef..9ccdcdbf0e7e 100644
> >>> --- a/drivers/vfio/platform/Makefile
> >>> +++ b/drivers/vfio/platform/Makefile
> >>> @@ -5,6 +5,7 @@ vfio-platform-y := vfio_platform.o
> >>>  obj-$(CONFIG_VFIO_PLATFORM) += vfio-platform.o
> >>>  obj-$(CONFIG_VFIO_PLATFORM) += vfio-platform-base.o
> >>>  obj-$(CONFIG_VFIO_PLATFORM) += reset/
> >>> +obj-$(CONFIG_VFIO_PLATFORM) += msi/
> >>>
> >>>  vfio-amba-y := vfio_amba.o
> >>>
> >>> diff --git a/drivers/vfio/platform/msi/Kconfig b/drivers/vfio/platform/msi/Kconfig
> >>> new file mode 100644
> >>> index 000000000000..54d6b70e1e32
> >>> --- /dev/null
> >>> +++ b/drivers/vfio/platform/msi/Kconfig
> >>> @@ -0,0 +1,9 @@
> >>> +# SPDX-License-Identifier: GPL-2.0-only
> >>> +config VFIO_PLATFORM_BCMPLT_MSI
> >>> +     tristate "MSI support for Broadcom platform devices"
> >>> +     depends on VFIO_PLATFORM && (ARCH_BCM_IPROC || COMPILE_TEST)
> >>> +     default ARCH_BCM_IPROC
> >>> +     help
> >>> +       Enables the VFIO platform driver to handle msi for Broadcom devices
> >>> +
> >>> +       If you don't know what to do here, say N.
> >>> diff --git a/drivers/vfio/platform/msi/Makefile b/drivers/vfio/platform/msi/Makefile
> >>> new file mode 100644
> >>> index 000000000000..27422d45cecb
> >>> --- /dev/null
> >>> +++ b/drivers/vfio/platform/msi/Makefile
> >>> @@ -0,0 +1,2 @@
> >>> +# SPDX-License-Identifier: GPL-2.0
> >>> +obj-$(CONFIG_VFIO_PLATFORM_BCMPLT_MSI) += vfio_platform_bcmplt.o
> >>> diff --git a/drivers/vfio/platform/msi/vfio_platform_bcmplt.c b/drivers/vfio/platform/msi/vfio_platform_bcmplt.c
> >>> new file mode 100644
> >>> index 000000000000..a074b5e92d77
> >>> --- /dev/null
> >>> +++ b/drivers/vfio/platform/msi/vfio_platform_bcmplt.c
> >>> @@ -0,0 +1,49 @@
> >>> +// SPDX-License-Identifier: GPL-2.0
> >>> +/*
> >>> + * Copyright 2020 Broadcom.
> >>> + */
> >>> +
> >>> +#include <linux/module.h>
> >>> +#include <linux/device.h>
> >>> +#include <linux/interrupt.h>
> >>> +#include <linux/msi.h>
> >>> +#include <linux/vfio.h>
> >>> +
> >>> +#include "../vfio_platform_private.h"
> >>> +
> >>> +#define RING_SIZE            (64 << 10)
> >>> +
> >>> +#define RING_MSI_ADDR_LS     0x03c
> >>> +#define RING_MSI_ADDR_MS     0x040
> >>> +#define RING_MSI_DATA_VALUE  0x064  
> >> Those 3 defines would not be needed anymore with that implementation option.  
> >>> +
> >>> +static u32 bcm_num_msi(struct vfio_platform_device *vdev)
> >>> +{
> >>> +     struct vfio_platform_region *reg = &vdev->regions[0];
> >>> +
> >>> +     return (reg->size / RING_SIZE);
> >>> +}
> >>> +
> >>> +static struct vfio_platform_msi_node vfio_platform_bcmflexrm_msi_node = {
> >>> +     .owner = THIS_MODULE,
> >>> +     .compat = "brcm,iproc-flexrm-mbox",
> >>> +     .of_get_msi = bcm_num_msi,
> >>> +};
> >>> +
> >>> +static int __init vfio_platform_bcmflexrm_msi_module_init(void)
> >>> +{
> >>> +     __vfio_platform_register_msi(&vfio_platform_bcmflexrm_msi_node);
> >>> +
> >>> +     return 0;
> >>> +}
> >>> +
> >>> +static void __exit vfio_platform_bcmflexrm_msi_module_exit(void)
> >>> +{
> >>> +     vfio_platform_unregister_msi("brcm,iproc-flexrm-mbox");
> >>> +}
> >>> +
> >>> +module_init(vfio_platform_bcmflexrm_msi_module_init);
> >>> +module_exit(vfio_platform_bcmflexrm_msi_module_exit);  
> >> One thing I would like to discuss with Alex.
> >>
> >> As the reset module is mandated (except if reset_required is forced to
> >> 0), I am wondering if we shouldn't try to turn the reset module into a
> >> "specialization" module and put the msi hooks there. I am afraid we may
> >> end up having modules for each and every vfio platform feature
> >> specialization. At the moment that's fully bearable but I can't predict
> >> what's next.
> >>
> >> As the mandated feature is the reset capability maybe we could just keep
> >> the config/module name terminology, tune the kconfig help message to
> >> mention the msi support in case of flex-rm?
> >>  
> > As I understand, your proposal is that we should not have a separate
> > module for MSI, rather we add in the existing reset module for
> > flex-rm. Thus, this way reset modules do not seem to be specialized
> > just for reset functionality only but for MSI as well. Apart from this
> > we need not to load the proposed msi module in this patch series. Is
> > my understanding correct?  
> 
> yes it is.
> > For me it looks OK to consolidate MSI in the existing 'reset' module.
> > Let me know your views so that I can work for the next patch set accordingly.  
> 
> Before you launch into the rewriting I would like to get the
> confirmation Alex is OK or if he prefers to keep separate modules.

If I understand correctly, the proposal here creates an entirely
parallel vfio-msi request module interface like we have for vfio-reset,
so the question is whether we should simplify vfio-platform-core to do
a single module request per compat string and the device specific
module would register multiple features rather than one per module.  Is
that right?

It seems the submodules are pretty simple, there's not a lot to be
gained from duplicate boilerplate code in the modules themselves.  The
core code would clearly be simplified slightly to avoid multiple module
requests, but for a more grand benefit is seems the registration
interfaces would also need to be consolidated, perhaps providing a
feature "ops" structure.  As you indicate, having only two features at
this point with a fairly small number of modules each, it's not yet too
burdensome, but I could imagine it being a useful project.

More importantly in the short term, I'd expect modules handling the
same compat string to be named similarly and enabled by a common
Kconfig option.  Thanks,

Alex

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