linux-kernel - Re: [PATCH] firmware_class: Add firmware filename overrides

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Message-ID: <CAJ34Pp7nK-4JiqkBSx25PaSDtRO8P6cJQsOuwKxaeuN9j_q6AA@mail.gmail.com>
Date:	Thu, 5 Mar 2015 09:52:23 -0800
From:	Charles Mooney <charliemooney@...gle.com>
To:	Marcel Holtmann <marcel@...tmann.org>
Cc:	Ming Lei <ming.lei@...onical.com>,
	Dmitry Torokhov <dtor@...omium.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] firmware_class: Add firmware filename overrides

On Thu, Mar 5, 2015 at 9:39 AM, Marcel Holtmann <marcel@...tmann.org> wrote:
> Hi Charles,
>
>> Specifically this was motivated by a situation where we have one
>> device with a dual-sourced touchscreen. Both use the same driver but
>> have different hardware & fw. Our FW updating software therefore,
>> needs to be able to update with the correct FW and detect all this at
>> runtime due to a read-only partition (so moving the firmware binaries
>> around isn't really an option)
>> Here the device has only one touchscreen at a time, but it isn't known
>> until run-time which will be present.
>>
>> So in this case the driver is serving the same function in each
>> situation (running a touchscreen) but may be working with different
>> hardware.
>>
>> Another situation where I've personally wanted this functionality is
>> on a device that uses the same touch driver for both a touchscreen and
>> a touchpad on the same device. If the driver only grabs a copy of FW
>> from, say, /lib/firmware/touch_fw.bin then you either need to move the
>> firmware binaries around on disk to update either device, or have a
>> change like this that allows you to override which filename it loads.
>> The moving option is not viable if you're using a RO filesystem.
>
> what is the actual problem here? We have drivers that load multiple firmware files and we have drivers that pick a different firmware depending on some parameters it reads from the device.
>
> Seems this is all possible already at the moment with the existing framework. You just need to update the drivers to operate properly.
>
> Regards
>
> Marcel
>

I totally agree, this functionality is not novel.  We could have added
this feature into the specific driver in question, but then we will
have to do the same thing on all the other drivers we might want to do
this on.  I guess the real problem that this solves is by adding the
change here, it allows you to override firmware names for *any* driver
without having to duplicate the functionality in each one as they come
up.

For a specific instance, here at ChromiumOS we have devices that use
Atmel, Cypress, Synaptics, and Elan touchpads and touchscreens that
all can encounter this issue.  The Atmel driver has a similar version
of this feature baked into it but the others don't.  We could add a
fw_filename attribute to each of these drivers, but then it would have
to be maintained across (at least) four drivers.
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