netdev - Re: [PATCH 0/3] ixgbe: request_firmware for configuration parameters

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Date:	Fri, 16 Aug 2013 15:14:31 -0700
From:	Ali Ayoub <ali@....mellanox.co.il>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	Shannon Nelson <shannon.nelson@...el.com>, netdev@...r.kernel.org,
	davem@...emloft.net, dwmw2@...radead.org,
	jeffrey.t.kirsher@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] ixgbe: request_firmware for configuration parameters

On 1/11/2013 11:41 AM, Greg KH wrote:
> On Fri, Jan 11, 2013 at 11:30:54AM -0800, Shannon Nelson wrote:
>> On Fri, Jan 11, 2013 at 10:25 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
>>> On Thu, Jan 10, 2013 at 06:02:20PM -0800, Shannon Nelson wrote:
>>>> Most networking dials and knobs can be set using ethtool, ifconfig, ip link
>>>> commands, or sysfs entries, all of which can be driven by startup scripts
>>>> and other configuration tools.  However, they all depend on having a netdev
>>>> already set up, and we have some low-level device functionality that needs
>>>> to be sorted out before we start setting up MSI-x and memory allocations.
>>
>>> Ick, please don't abuse request_firmware() for this type of thing.
>>
>> Yeah, it seemed ugly to me at first as well, but it grew on me as I
>> realized that it does solve a problem in a rather elegant way.  While
>> working this up I discussed this with Mr. Woodhouse thinking that as a
>> firmware tree maintainer he'd have a similar reaction, but he actually
>> wasn't opposed to it (David, please speak up if I'm misrepresenting
>> your comments).
> 
> David maintains the external firmware tree repo, not the in-kernel
> firmware core code (which I used to maintain.)
> 
>>> What's wrong with configfs?  It sounds like it will fit your need, and
>>> that is what is created for.
>>
>> configfs has similar problems as sysfs - the driver needs to create
>> the hooks before it has all the info it might need for some hooks,
>> there is no persistence across reboots, and I don't think it will help
>> for initrd images.  Additionally, there would need to be some userland
>> mechanism to notice that the hooks were there and to feed it the
>> startup info.  Using a file in the firmware path gives us persistence
>> and a way for the driver to get info before having to set up
>> filesystem hooks.  It also gives us a way to get special config info
>> into the boot image.  And the whole mechanism already exists,
>> including UDEV hooks that can do more fancy stuff if needed.
> 
> Yes, but you are now starting to use "configuration files" for kernel
> drivers, which we have resisted for 20+ years for a variety of good
> reasons. You can't just ignore all of the arguments to not do this all
> of a sudden because you feel your driver is somehow "special" here.

Other device drivers of other vendors (not only netdevs) need such a
mechanism as well, I think it's a general requirement for many drivers
that normally need low level configurations for device initialization in
the very first stage of the driver load.

> All of the above issues you seem to have with sysfs and configfs can be
> resolved with userspace code, and having your driver not do anything to
> the hardware until it is told to by userspace.

To tell the driver not to do anything until it's configured by a
userspace code will require a module param for non-default-configs
(which brings us back to the original argument of avoiding module params).

By having userspace code to feed configfs/sysfs nodes, and making it
available in initrd; we will end up having similar mechanism to
request_firmware().

I think this kind of "low level init configuration" can be seen as a
firmware configuration, we can put some limitation on fetching the
config file, or propose a new function such as request_firmware_config()
that uses the same uevent hooks, and leverages the available userspace
tools that already supported in initrd and meant to serve the same
purpose - of feeding the driver the suitable firmware and configuration
to get started.

Ali;
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