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Date:   Tue, 31 Oct 2023 07:58:00 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Tingwei Zhang <quic_tingweiz@quicinc.com>
Cc:     Masami Hiramatsu <mhiramat@kernel.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        linux-kernel@vger.kernel.org, Trilok Soni <quic_tsoni@quicinc.com>,
        Jinlong Mao <quic_jinlmao@quicinc.com>
Subject: Re: How to pass software configuration to driver built as module in
 boot up phase
Message-ID: <2023103108-guacamole-neurotic-f59b@gregkh>
References: <1c001c6f-9902-4803-9406-39e3325422bf@quicinc.com>
 <2023103021-revolving-clapper-632d@gregkh>
 <c244eae0-d3d8-414b-8d1f-c902bd46bd61@quicinc.com>
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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