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    SubjectRE: [RFC PATCH 0/2] add support for CDX bus MSI domain
    Date
    [AMD Official Use Only - General]



    > -----Original Message-----
    > From: Robin Murphy <robin.murphy@arm.com>
    > Sent: Wednesday, August 3, 2022 7:46 PM
    > To: Gupta, Nipun <Nipun.Gupta@amd.com>; linux-kernel@vger.kernel.org;
    > linux-arm-kernel@lists.infradead.org; gregkh@linuxfoundation.org;
    > rafael@kernel.org; maz@kernel.org; tglx@linutronix.de
    > Cc: okaya@kernel.org; Anand, Harpreet <harpreet.anand@amd.com>;
    > Simek, Michal <michal.simek@amd.com>; Agarwal, Nikhil
    > <nikhil.agarwal@amd.com>
    > Subject: Re: [RFC PATCH 0/2] add support for CDX bus MSI domain
    >
    > [CAUTION: External Email]
    >
    > On 2022-08-03 13:26, Nipun Gupta wrote:
    > > Devices in FPGA can be added/modified dynamically on run-time.
    > > These devices are exposed on system bus to embedded CPUs.
    > >
    > > CDX is an upcoming bus, that caters to the requirement for
    > > dynamically discovered FPGA devices. These devices are added
    > > as platform devices where fwnode is created using 'software
    > > nodes' in Linux framework.
    > >
    > > This RFC targets to solves 2 issues when adding devices
    > > dynamically using platform_device_register API.
    > >
    > > 1. It creates a MSI domain for CDX bus devices, which can
    > > discover device ID used by GIC ITS without depending
    > > on of_node.
    > > 2. Since these devices are not present in device tree, it
    > > creates a sysfs entry to expose the compatible string.
    >
    > Isn't this pretty much what CONFIG_OF_DYNAMIC is for? From the look of
    > these patches this thing is still completely tied to devicetree, so why
    > reinvent that wheel?

    According to our analysis, device tree modification via OF_DYNAMIC is
    mostly designed as a boot time patching mechanism but it was never
    designed to be runtime used as a "bus" mechanism.

    Most firmware patches ACPI/DT during boot but we want to go beyond
    boot time configuration and would like to be able to dynamically
    remove/insert objects during FPGA servicing. As an example, a new FPGA
    can be programmed to the system where either the attributes are
    changed or new devices are introduced.

    Another concern about OF_DYNAMIC is about security.
    We'd like to keep device-tree contents intact at boot and never
    touch again as a good security principle.

    >
    > Robin.
    >
    > > Nipun Gupta (2):
    > > irqchip: cdx-bus: add cdx-MSI domain with gic-its domain as parent
    > > driver core: add compatible string in sysfs for platform devices
    > >
    > > drivers/base/platform.c | 15 +++
    > > drivers/irqchip/Makefile | 1 +
    > > drivers/irqchip/irq-gic-v3-its-cdx-msi.c | 114 +++++++++++++++++++++++
    > > include/linux/cdx/cdx.h | 15 +++
    > > 4 files changed, 145 insertions(+)
    > > create mode 100644 drivers/irqchip/irq-gic-v3-its-cdx-msi.c
    > > create mode 100644 include/linux/cdx/cdx.h
    > >
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