[Buildroot] Buildroot: enable lib/firmware/brcm for rpi0w

[Peter Seiderer <ps.report@gmx.net>]

Hello Andreas,

On Fri, 26 Mar 2021 12:47:21 +0000, Andreas Ziegler <br015@umbiko.net> wrote:

> Hello Peter,
>
> On 2021-03-25 21:20, Peter Seiderer wrote:
> >
> > Many thanks for doing the tests!
> >
>
> Not at all; after getting confused with different versions and
> repositories, I wanted to understand the reason behind this.
>
> Short summary of my findings; I may state the obvious here, but it was
> new for me and maybe it helps someone with the same hazy knowledge about
> hardware engineering as myself:
>
> Broadcom sold its RF division to Cypress in 2016. Cypress now supports
> the legacy wireless /bluetooth /radio hardware from Broadcom; that is
> the reason why BCM* and CYW* versions of firmware exist, and
> linux-firmware removed the original Broadcom supplied binaries.
>
> Cypress does not directly sell to end customers, but provides silicon to
> hardware partners (AzureWave, Murata, ...), which in turn sell RF
> solutions. Cypress distributes firmware for their silicon chips
> (probably to same hardware partners).
>
> End product is some type of SOC (subsystem on chip); the benefit is that
> tuning and regulatory issues have been taken care of. The SOC
> manufacturer is responsible for supplying bluetooth patch (HCD),
> regulatory data (CLM) and firmware configuration (TXT).
>
> That means the firmware binary (BIN) can be obtained from any source,
> the other items (HCD, CLM, TXT) need to be sourced from the implementer.
>
> >> The LibreELEC repository (rpi-wifi-firmware) seems to have adopted
> >> this
> >> version in commit 7dbd877545ae15069f2bd0e73893af942500e23d on Jan. 25.
> >
> > So a good reason to stay with LibreELEC (and fix the firmware package
> > to
> > provide raspberrypi,4-model-b.txt as a link or copy, do you know if
> > missing
> > it has some disadvantages or produces only the firmware load warning or
> > is
> > there a fallback to plain brcmfmac43455-sdio.txt?), keeping up with
> > RPi-Distro...
>
> Yes, also my opinion to stay with LibreELEC. The repository is small, is
> updated in a timely manner, and is (slightly) better documented than
> RPi-Distro.
>
> There is one thing (apart from providing the missing link) I would
> propose: merge rpi-bt-firmware and rpi-wifi-firmware into
> rpi-rf-firmware, combining the code from both .mk and Config.in files.
> Functionality would be identical, but one less firmware package. If
> anyone is interested, I could provide a patch.

+1 from my side...

>
> In recent kernels, firmware load tries board-specific path first, then
> falls back to firmware derived path [1]. If I remember correctly, in
> kernels < 5.0 the firmware load failed.
>
> >> There seem to be some bigger changes in the pipeline: linux-firmware
> >> removed the Broadcom redistributed binaries in January [4] for the
> >> 20210208 release; instead Cypress firmware should be used. The
> >> upstream
> >> repository for this firmware seems to be murata-wireless /
> >> cyw-fmac-fw [5]
> >>
> >> I need to look into this in detail at some other time ...
> >
> > Seems kind of (another) firmware mess...., different versions at
> > different
> > repositories...., all with the same name (instead of clear version
> > string)...
>
> There are at least three different versions available in Buildroot:
>
> (available in Buildroot, repo 'master' version listed respectively)
>    libreELEC		build 2021-01-04	version 7.45.229
>    linux-firmware	build 2020-09-18	version 7.45.221
>    murata-wireless	build 2020-09-18	version 7.45.221
> (not in buildroot)
>    rpi-distro		build 2021-01-04	version 7.45.229
>
> > Regards,
> > Peter
>
> Kind regards,
> Andreas

Thanks again for the detailed information (and testing)!

Did just sent out an patch adding the convenience firmware configuration
links for RPi3A+, RPi3B+ and RPi4B (see [2])...

Regards,
Peter

[2] https://patchwork.ozlabs.org/project/buildroot/patch/20210329184503.10514-1-ps.report at gmx.net/

>
> [1]
> https://elixir.bootlin.com/linux/v5.10.21/source/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c#L616
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