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    SubjectRe: How to pass software configuration to driver built as module in boot up phase
    On Tue, Oct 31, 2023 at 10:56:23AM +0800, Tingwei Zhang wrote:
    > On 10/30/2023 7:30 PM, Greg Kroah-Hartman wrote:
    > > On Mon, Oct 30, 2023 at 07:21:48PM +0800, Tingwei Zhang wrote:
    > > > Hi Masami, Greg and Rafael,
    > > >
    > > > I have one driver that needs a bunch to software configuration like 1000
    > > > settings. These settings can be different according to the use case.
    > >
    > > That seems very odd, what type of driver is this?
    > The example use case is below DCC driver which is a DMA engine. It can be
    > configured to read/write registers while whose registers need to be
    > configured by software. It's mainly used to debug device crash issue.
    > https://lore.kernel.org/lkml/cover.1691496290.git.quic_schowdhu@quicinc.com/T/

    Given that no one listened to my last review cycle of that driver, why
    are you asking us again?

    > > > They are required in boot up phase so we can't reply on user space to make
    > > > the configuration.
    > > >
    > > > Boot config is not preferred since we'd like to build that driver as dynamic
    > > > load Kernel module.
    > > >
    > > > Could you let me know if there's any mechanism in Kernel to do that?
    > >
    > > What is wrong with the existing ways of doing this that all other
    > > drivers use?
    > I'm not aware of all the existing ways. Below ways are what I know and they
    > may not be suitable for some reason.
    > 1. Let user space to configure with sysfs/debugfs/ioctl interface. Since we
    > need this configuration to be done in early stage before user space is up.

    I really doubt that you need this before userspace starts, as that's not
    what "device crash" stuff should be dealing with. That happens after
    init starts, because you have a working kernel (i.e. this is not for
    hardware bringup.)

    > This doesn't work.

    Why do you need this before init? Specific reasons please.

    > 2. Use device tree to pass the configuration to driver. Since the
    > configuration is software configuration instead of hardware descirption. It
    > doesn't fit in device tree.
    > 3. Boot config or commandline parameter. If the driver is built in, it can
    > work. But it doesn't work for dynamically loadable Kernel module.

    If you have a module, then you can do this after init starts, so you
    are reporting conflicting "requirements" here, which make this
    impossible for us to understand :(

    Please work with the kernel developers at your company to come up with a
    solution for this, you have the experience, do not require the community
    to do your work for you.

    thanks,

    greg k-h

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