Re: [PATCH] firmware_class: Add firmware filename overrides

[Ming Lei]

On Thu, Mar 5, 2015 at 8:48 AM, Dmitry Torokhov <dtor@xxxxxxxxxxxx> wrote:
> On Wed, Mar 04, 2015 at 03:57:09PM -0800, Greg KH wrote:
>> On Wed, Mar 04, 2015 at 03:25:10PM -0800, Charlie Mooney wrote:
>> > This patch adds an additional feature to the firmware_class.c module.
>> > To allow a unified method of specifying new firmware locations when
>> > drivers request a firmware binary to update their devices with, we
>> > have added the concept of a "fw override"
>> >
>> > A fw override is a rule that matches firmware requests based on the
>> > name of the device requesting the fw and what the filename for the
>> > fw they are requesting is, and overrides their requests with a new
>> > value.
>> >
>> > Overrides are set up by piping a description of the override into
>> > an attribute set up at /sys/class/firmware/fw_override.  The string
>> > should be a null-deliminited list of the firmware name you want to
>> > over ride, the new name to replace it with, and the device name that
>> > you want the override to apply to.   For example you could set up
>> > an override for a device called "my_device" so that any time it
>> > requests a firmware called "my_fw.bin" it instead gets "new_fw.bin"
>> > with the following command:
>> >
>> > echo -e 'my_fw.bin\0new_fw.bin\0my_device\0' >
>> >                             /sys/class/firmware/fw_override
>>
>> I hate to ask, but I have to, why do you need this?
>
> We may have single driver serve several devices (a touchscreen and a
> touchpad) that require different firmware/config file to function. We have

I remember some wifi drivers have similar usage too: one driver serves
several functions, and each function need its own firmware. So looks
it is fine to use different firmware name for each different function, or
my understanding about the use case is wrong?

Thanks,
Ming Lei

> several options:
>
> - modify the driver to allow changing firmware name from userspace - gets
>   old when there are several drivers that need that;
> - encode part numbers in the driver and request different firmware - not
>   easily maintainable, still has an issue that same part might be used for
>   different devices;
> - replace the firmware file on disk before initiating firmware load - does
>   not work well with read-only file systems;
> - have udev supply different data - udev went out of fashion;
> - have one central place (firmware loader) that users can control to
>   override the names - this solution.
>
> Thanks.
>
> --
> Dmitry
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