Re: [RFC] ath10k: silence firmware file probing warnings

[Arend Van Spriel <arend.vanspriel@broadcom.com>]

On 22-7-2016 12:26, Stanislaw Gruszka wrote:
> On Fri, Jul 22, 2016 at 10:38:24AM +0200, Arend Van Spriel wrote:
>> + Luis
>>
>> On 21-7-2016 13:51, Stanislaw Gruszka wrote:
>>> (cc: firmware and brcmfmac maintainers)
>>>
>>> On Thu, Jul 21, 2016 at 06:23:11AM -0400, Prarit Bhargava wrote:
>>>>
>>>>
>>>> On 07/21/2016 04:05 AM, Stanislaw Gruszka wrote:
>>>>> On Thu, Jul 21, 2016 at 10:36:42AM +0300, Emmanuel Grumbach wrote:
>>>>>> On Thu, Jul 21, 2016 at 10:09 AM, Stanislaw Gruszka <sgruszka@redhat.com> wrote:
>>>>>>> On Tue, Jul 19, 2016 at 03:00:37PM +0200, Michal Kazior wrote:
>>>>>>>> Firmware files are versioned to prevent older
>>>>>>>> driver instances to load unsupported firmware
>>>>>>>> blobs. This is reflected with a fallback logic
>>>>>>>> which attempts to load several firmware files.
>>>>>>>>
>>>>>>>> This however produced a lot of unnecessary
>>>>>>>> warnings sometimes confusing users and leading
>>>>>>>> them to rename firmware files making things even
>>>>>>>> more confusing.
>>>>>>>
>>>>>>> This happens on kernels configured with
>>>>>>> CONFIG_FW_LOADER_USER_HELPER_FALLBACK and cause not only ugly warnings,
>>>>>>> but also 60 seconds delay before loading next firmware version.
>>>>>>> For some reason RHEL kernel needs above config option, so this
>>>>>>> patch is very welcome from my perspective.
>>>>>>>
>>>>>>
>>>>>> Sorry for my ignorance but how does the firmware loading work if not
>>>>>> with udev's help?
>>>>>
>>>>> I'm not sure exactly, but I think kernel VFS layer is capable to copy
>>>>> file data directly from mounted filesystem without user space helper.
>>>>
>>>> Here's the situation: request_firmware() waits 60 seconds for udev to do its
>>>> loading magic via a "usermode helper".  This delay is there to allow, for
>>>> example, userspace to unpack or download a new firmware image or verify the
>>>> firmware image *in userspace* before providing it to the driver to apply to the HW.
>>>>
>>>> Why 60 seconds?  It is arbitrary and there is no way for udev & the kernel to
>>>> handshake on completion.
>>>>
>>>>>
>>>>>> As you can imagine, iwlwifi is suffering from the
>>>>>> same problem and I would be interested in applying the same change,
>>>>>> but I'd love to understand a bit more :)
>>>>>
>>>>> Yes, iwlwifi (and some other drivers) suffer from this. However this
>>>>> happen when the newest firmware version is not installed on the system
>>>>> and CONFIG_FW_LOADER_USER_HELPER_FALLBACK is enabled. What I suppose
>>>>> it's not common.
>>>>
>>>> request_firmware_direct() was introduced at my request because (as you've
>>>> noticed) when CONFIG_FW_LOADER_USER_HELPER_FALLBACK=y drivers may stall for long
>>>> periods of time when starting.  The bug that this introduced was a 60 second
>>>> delay per logical cpu when starting a system.  On a 64 cpu system that meant the
>>>> boot would complete in a little over one hour.
>>>>
>>>>>
>>>>> I started to see this currently, because that option was enabled on 
>>>>> RHEL kernel. BTW: I think Prarit iwlwifi thermal_zone problem was
>>>>> happened because of that, i.e. thermal device was not functional
>>>>> because f/w wasn't loaded due to big delay.
>>>>>
>>>>> I'm not sure if replacing to request_firmware_direct() is a good
>>>>> fix though. For example I can see this problem also on brcmfmac, which
>>>>> use request_firmware_nowait(). I think I would rather prefer special
>>>>> helper for firmware drivers that needs user helper and have
>>>>> request_firmware() be direct as default.
>>>>>
>>>>
>>>> The difference between request_firmware_direct() and request_firmware() is that
>>>> the _direct() version does not wait the 60 seconds for udev interaction.  The
>>>> only userspace check performed is to see if the file is there, and if the file
>>>> does exist it is provided to the driver to be applied to the hardware.
>>>>
>>>> So the real question to ask here is whether or not the ath10k, brcmfmac, and
>>>> iwlwifi require udev to do anything beyond checking for the existence and
>>>> loading the firmware image.  If they don't, then it is better to use
>>>> request_firmware_direct().
>>>
>>> They don't need that, like 99% of the drivers I think, hence changing the
>>> default seems to be more reasonable. However changing 3 drivers would work
>>> for me as well, and that change do not introduce risk of broking drivers
>>> that require udev fw download.
>>>
>>> iwlwifi and ath10k are trivial, bcrmfmac is a bit more complex as it
>>> use request_firmware_nowait(), so it first need to be converted to
>>> ordinary request_firmware(), but this should be doable and I can do
>>> that.
>>
>> I am going bonkers here. This is the Nth time a discussion pops up on
>> firmware API usage. I stopped counting N :-( So the first issue was that
>> the INIT was taking to long as we were requesting firmware during probe
>> which was executed in the INIT context. So we added a worker and
>> register the driver from there. There was probably a reason for
>> switching to _no_wait() as well, but I do not recall the details. The
>> things is I don't know if I need user-space or not. I just need firmware
>> to get the device up and running. We have changed our driver a couple of
>> times now to accommodate something that in my opinion should have been
>> abstracted behind the firmware API in the first place and now here is
>> another proposal to change the drivers. Come on!
> 
> I understand you dislike that :-) Just to clarify the issue here:
> 
> Some drivers (including brcmfmac) request new firmware images, which are
> not yet available (i.e. development F/W versions) and then fall-back
> to older firmware version and works perfectly fine.
> 
> However with CONFIG_FW_LOADER_USER_HELPER_FALLBACK=y configured, in case
> of missing F/W image, request firmware involve user space helper and
> waits 60s (loading_timeout value from drivers/base/firmware_class.c),
> what delays creating network interface and confuse users.
> 
> For brcmfmac this looks like this:
> 
> [   15.160923] brcmfmac 0000:03:00.0: Direct firmware load for brcm/brcmfmac4356-pcie.txt failed with error -2
> [   15.170759] brcmfmac 0000:03:00.0: Falling back to user helper
> <snip>
> [   75.709397] brcmfmac: brcmf_c_preinit_dcmds: Firmware version = wl0: Oct 22 2015 06:16:41 version 7.35.180.119 (r594535) FWID 01-1a5c4016
> [   75.736941] brcmfmac: brcmf_cfg80211_reg_notifier: not a ISO3166 code (0x30 0x30)
> 
> Without CONFIG_FW_LOADER_USER_HELPER_FALLBACK first firmware request
> silently fail and then instantly next F/W image is loaded.
> 
> Another option to solve to problem would be stop requesting not
> available publicly firmware. However, I assume some drivers would
> like to preserve that option.

Actually, this is not the case with brcmfmac. We do need a firmware
file, ie. brcm/brcmfmac4356-pcie.bin, and also request for a nvram file,
ie. brcm/brcmfmac4356-pcie.txt. The latter is optional and the device
works fine without it.

What is still unclear to me is when request_firmware_direct() would fail
and in what circumstances the udev helper is a valid callback. Can you
explain such a scenario. Another question I have is what the reasons are
behind the 60 seconds timeout.

>>> However I wonder if changing that will not broke the case when
>>> driver is build-in in the kernel and f/w is not yet available when
>>> driver start to initialize. Or maybe nowadays this is not the case
>>> any longer, i.e. the MODULE_FIRMWARE macros assure proper f/w 
>>> images are build-in in the kernel or copied to initramfs?
>>
>> That is a nice idea, but I have not seen any change in that area. Could
>> have missed it.
> 
> I believe this is how the things are already done, IOW switching to
> request_firmware_direct() in the driver should be no harm.

Ok. What are the consequences when:
- driver is built-in.
- driver+firmware present on initramfs.
- driver on initramfs, firmware only present on rootfs.
- driver+firmware only on rootfs.

I assume the third one would be considered a configuration issue.

Regards,
Arend