[Replicant] LTE support in Replicant 6 and 9 (was: Replicant 6.0 0004 RC1)

[Kurtis Hanna]

Hello Sam,

Sam Noble:
> On Wed, Jan 15, 2020 at 01:41:21AM +0100, Denis 'GNUtoo' Carikli wrote:
>> On Tue, 14 Jan 2020 14:31:36 +0000
>> Josh Branning <lovell.joshyyy at gmail.com> wrote:
>> The I9305 modem should be supported by upstream Linux, but I don't know
>> if the support is fully complete, or how loading its firmware with such
>> kernel. 
> 
> While we're talking i9305, how closely has anyone looked at the n7105
> (LTE Note II) am I being overly optimistic in imagining that when/if the
> ofono_rild for i9305 is working the n7105 will follow shortly behind? 
> Or are there more differences between the two than I'm envisioning?
> 

The oFono work that has been done so far in Replicant 6 was done on the
SGH-T889, the T-Mobile version of the Note II. This was because the
developer, Joey Hewitt, is based in the United States and the LTE bands
supported by the i9305 doesn't work with US carriers. You can see the
status of this work here: https://redmine.replicant.us/issues/1958

The schematics for the SGH-T889 are here:
https://fcc.report/FCC-ID/A3LSGHT889/1797529ACPM-7500-SG1

The schematics say that the SGH-T889's cellular modem is the Qualcomm
MDM8215M. It is my understanding that the i9305 uses the Qualcomm MDM9615.

Issue #1958 says that the LTG oFono work that was done on the SGH-T889
might be able to be ported to the i9305, but to test this, it would
require using the proper manifest and someone porting a patch like this
and its parent patch to the i9305 device tree:
https://git.replicant.us/contrib/scintill/device_samsung_t0lte/commit/?h=replicant-6.0&id=e11c95a091cd8b1dbdda8307565283b0c2377de2

It is my understanding that this porting and testing work hasn't started
yet by any European Replicant developers.

If we are able to prove that Joey's oFono work on the SGH-T889 version
of the Note II can be ported to the i9305 we could then have a device
that American Replicant developers could hack on to work out the bugs
and a device that European Replicant developers could hack onto work out
bugs, hopefully resulting in two devices that both support LTE in
Replicant 6.

This would then perhaps allow us to add support for more LTE versions of
the Note II, S3, and Note 8.0 listed here:
https://redmine.replicant.us/projects/replicant/wiki/Exynos4412Devices.
This might even include some CDMA device support, unless I'm mistaken
about how to add support for that.

The issue of Replicant 9 is a different one. Since Replicant 9 will use
the upstream kernel, and since neither the N7100 nor the N7105 have
their display drivers upstreamed, they currently don't have the
foundational conditions required for support for Replicant 9 so it
doesn't make sense currently to work on peripheral issues like modem
support.

While I don't think that we have a support matrix for the upstream
status of the N7100 nor the N7105 on Replicant's wiki, this issue to
referenced here:
https://redmine.replicant.us/projects/replicant/wiki/GalaxyNote2N7105#For-Replicant-9

There is a support matrix for the upstream status for the N7100 and
N7105 on forkbomb's website here:
https://blog.forkwhiletrue.me/pages/midas-mainline/ I think that this
was recently updated by forkbomb at the request of Denis, so I think it
is currently up to date.

Based on the links on that matrix, it looks like most of forkbomb's Note
II display work can be found in the more recent commits in his
wip/t0-display branch here:
https://github.com/fourkbomb/linux/commits/wip/t0-display

I don't know if any of these Note II display patches have been submitted
upstream for review yet. I don't think they have.

As for the i9305, we are much closer to having upstream kernel support.
It is my understanding that it currently mainly only lacks upstream
support for the Qualcomm modem. Since its Qualcomm MDM9615 modem is
currently already in the upstream kernel due to it being added for
another device, we might be able to just add it to the i9305's Device
Tree Reference and see if it works and make some tweaks if it doesn't.
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/log/drivers/clk/qcom/gcc-mdm9615.c

It is currently unknown how much of the upstream Qualcomm MDM9615 code
will need to be modified in order to also add upstream support for the
Qualcomm MDM8215M.

Once the Note II's display and MDM8215M modem is upstreamed though,
Joey's oFono code for Replicant 6 can begin to be ported to Replicant 9.

This is my currently understanding of the situation, at least. I hope it
helps!

In Solidarity,
Kurtis Hanna