linux-kernel - Re: [RFC v0 7/8] Input: ims-pcu: use firmware

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Date:	Mon, 1 Aug 2016 14:26:04 +0200
From:	Daniel Wagner <daniel.wagner@...-carit.de>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	Arend van Spriel <arend.vanspriel@...adcom.com>
CC:	Bjorn Andersson <bjorn.andersson@...aro.org>,
	Daniel Wagner <wagi@...om.org>,
	Bastien Nocera <hadess@...ess.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Johannes Berg <johannes.berg@...el.com>,
	Kalle Valo <kvalo@...eaurora.org>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	<linux-input@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
	<linux-wireless@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v0 7/8] Input: ims-pcu: use firmware_stat instead of
 completion

On 07/31/2016 09:23 AM, Dmitry Torokhov wrote:
> On July 30, 2016 9:58:17 AM PDT, "Luis R. Rodriguez" <mcgrof@...nel.org> wrote:
>> On Sat, Jul 30, 2016 at 02:42:41PM +0200, Arend van Spriel wrote:
>>> On 29-07-16 08:13, Daniel Wagner wrote:
>>>> On 07/28/2016 09:01 PM, Bjorn Andersson wrote:
>>>>> On Thu 28 Jul 11:33 PDT 2016, Dmitry Torokhov wrote:

>>> + Luis (again) ;-)

That was not on purpose :) My attempt to keep the Cc list a bit shorter 
was a failure.

>>>>>> Do not quite like it... I'd rather asynchronous request give out
>>>>>> firmware status pointer that could be used later on.
>>>
>>> Excellent. Why not get rid of the callback function as well and have
>>> fw_loading_wait() return result (0 = firmware available, < 0 = fail).
>>> Just to confirm, you are proposing a new API function next to
>>> request_firmware_nowait(), right?
>>
>> If proposing new firmware_class patches please bounce / Cc me, I've
>> recently asked for me to be added to MAINTAINERS so I get these
>> e-mails as I'm working on a new flexible API which would allow us
>> to extend the firmware API without having to care about the old
>> stupid usermode helper at all.

These patches here are a first attempt to clean up a bit of the code 
around the completion API. As Dmitry correctly pointed out, it makes 
more sense to go bit further and make the async loading a bit more 
convenient for the drivers.

> I am not sure why we started calling usermode helper "stupid". We
> only  had to implement direct kernel firmware loading because udev/stsremd
> folks had "interesting" ideas how events should be handled; but having
> userspace to feed us data is not stupid.

I was ignorant on all the nasty details around the firmware loading. If 
I parse Luis' patches correctly they introduce an API which calls 
kernel_read_file_from_path() asynchronously:

sysdata_file_request_async(..., &cookie)
   *coookie = async_schedule_domain(request_sysdata_file_work_func(), ..)

   request_sysdata_file_work_fun()
     _sysdata_file_request()
       fw_get_filesystem_firmware()
	kernel_read_file_from_path()

sysdata_synchronize_request(&cookie);

Doesn't look like what your asking for.

> If we want to overhaul firmware loading support we need to figure
> out  how to support case when a driver want to [asynchronously] request
> firmware/config/blob and the rest of the system is not ready. Even if we
> want kernel to do read/load the data we need userspace to tell kernel
> when firmware partition is available, until then the kernel should not
> fail the request.

I gather from Luis' blog post and comments that he is on the quest on 
removing userspace support completely.

Maybe this attempt here could be a step before. Step 1 would be changing 
request_firmware_nowait() to request_firmware_async so drivers don't 
have to come up with their own sync primitives, e.g.

   cookie = request_firmware_async()
   fw_load_wait(cookie)

Step 2 could be something more towards sysdata approach.

cheers,
daniel