Contributing a driver to mainline Linux takes significant time and effort up front. You can't just throw anything over the Linux fence and expect that already-overworked kernel maintainers keep tending for it for the next decades.

Slapping together a half-working out-of-tree kernel module and calling it a day is not only much cheaper; it also buys you the time you need to write the new driver for next year's hot shit SoC that smartphone vendors demand.

Precisely.

What would you want as a buyer. A driver that has already demonstrated that it is good enough to be included in the kernel, or one of unknown quality that may need extra work to integrate with the kernel.

I get why suppliers don't want to do the work. I just don't understand why there isn't enough value add for buyers to justify the premium for the benefits of a mainline driver, and/or why sellers don't try and capture that premium

I don't think buyers are actually going to pay enough for the sellers to justify the added cost. Remember that the buyers have to pass their costs on to their end customers (e.g. consumer phone purchasers), and those people won't accept all phones becoming $50 more expensive or whatever.

Also consider the cultural context. The culture of hardware manufacturers is much different than that of software vendors. They don't view software as a product, but more a necessary evil to make their hardware work with existing software infrastructure. They want to spend as little time on it as possible and then move onto the next thing.

I'm not endorsing this status quo, merely trying to explain it.

The way it seems to me is that a driver takes X hours to make, integrate, etc. It's cheaper for the vendor to spend those X hours, rather than each individual purchaser each spending those X hours.

Not a lot of software requires a bleeding edge kernel. If vendor B has a superior chip at a viable price it makes sense to go with them.

Because the buyers are consumer hardware companies. This means a) there's an expectation that software works just like their hardware: they put it together once and then throw it onto the market. Updating or supporting it is not a particular consideration, unless they re-engineer something significantly to reduce costs. and b) the bean-counters and hardware engineers have more sway than the software engineers: lower cost, better battery life, features, etc on paper will win out over good software support over the life of the product.

because you don't care to give the customer longer term software support

many consumers are not aware about the danger a unmaintained/non-updatable software stack introduces or that their (mainly) phone is unmaintained

so phone vendor buys from B because A is often just not an option (not available for the hardware you need) and then dumps the problem subtle and mostly unnoticeable on the user

there are some exceptions, e.g. Fairphone is committed to quite long term software support so they try to use vendor As or vendor Bs which have contractual long term commitment for driver maintaince

but in the space of phones (and implicit IoT using phone parts) sadly sometimes (often) the only available option for the hardware you need is vendor B where any long term diver maintenance commitment contracts are just not affordable if you are not operating on a scale of a larger phone vendor

E.g. as far as I remember Fairphone had to do some reserve engineering/patching to continue support for the FP3 until today (and well I think another 2 or so years), and I vaguely remember that they where somewhat lucky that some open source driver work for some parts was already ongoing and getting some support with some of the vendors. For the FP5 they manage to have a more close cooperation with Qualcomm allowing them to provide a 5 year extended warranty and target software support for 8 years (since release of phone).

So without phone producer either being legally forced to have a certain amount of software support (e.g. 3 years after last first party selling) or at least be largely visible transparent about the amount of software support they do provide upfront and also inform their user when the software isn't supported anymore I don't expect to see any larger industry wide changes there.

Through some countries are considering laws like that.

Sadly, far too often, software support simply nevers enter the picture in sourcing decisions. Back when I was privy to this process at an OEM, the only factors that mattered were:

1. Hit to the BOM (i.e. cost); and chip

2. Suppliability (i.e., can we get enough pieces, by the time we need them, preferably from fewer suppliers).

In the product I was involved in building (full OS, from bootloader to apps), I was lucky that the hardware team (separate company) was willing to base their decisions on my inputs. The hardware company would bear the full brunt of BOM costs, but without software the hardware was DOA and wouldn't even go to manufacturing. This symbiotic relationship, I think, is what made it necessary for them to listen to our inputs.

Even so, I agreed software support wasn't a super strong input because:

1. There's more room for both compromises and making up for compromises, in software; and

2. Estimating level of software support and quality is more nuanced than just a "Has mainline drivers?" checkbox.

For example, RPi 3B vs. Freescale iMX6. The latter had complete mainline support (for our needs) but the former was still out-of-tree for major subsystems. The RPi was cheaper. A lot cheaper.

I okayed RPi for our base board because:

1. Its out-of-tree kernel was kept up-to-date with mainline with a small delay, and would have supported the next LTS kernel by the time our development was expected to finish (a year);

2. Its out-of-tree code was quite easy (almost straightforward) to integrate into the Gentoo-based stack I wanted to build the OS on; and

3. I was already up-and-running with a prototype on RPi with ArchLinuxARM while we were waiting for iMX6 devkits to be sourced. If ArchLinuxARM could support this board natively, I figured it wouldn't be hard to port it to Gentoo; turned out Gentoo already had built-in support for its out-of-tree code.

Of course, not every sourcing decision was as easy as that. I did have to write a driver for an audio chip because its mainline driver did not support the full range of features the hardware did. But even in that case, the decision to go ahead with that chip was only made after I was certain that we could write and maintain said driver.

Yup, exactly. I last worked in this field in 2009, and BOM cost (tempered with component availability) was king. This was also a time when hardware was much less capable, so they usually ran something like vxWorks (or, ::shudder::, uClinux). Building the cheapest product that could get to market fastest (so as to beat competitors to the latest WiFi draft standard) was all that mattered.

Your Raspberry Pi example is IMO even more illustrative than you let on. I'll reiterate that even that platform is not open and doesn't have a full set of mainlined drivers, after a decade of incredibly active development, by a team that is much more dedicated to openness than most other device manufacturers. Granted, they picked a base (ugh, Broadcom) that is among the worst when it comes to documentation and open source, but I think that also proves a point: device manufacturers don't have a ton of choice, and need to strike a balance between openness and practical considerations. The Raspberry Pi folks had price and capability targets to go with their openness needs, and they couldn't always get everything they wanted.

The easy answer is that buyers largely don't care. Most people get their phones from their ISP provider, so that's the main target. They get a data plan that comes bundled with a phone and pay it off for 2 years. After 2 years they get a new plan with a new phone.

Caring about long-term maintenance isn't what most buyers do. Going SIM-only on your data plan is out of the ordinary.

Also in my experience people largely pick their phones based on the surface level hardware rather than the long-term reliability. Hence why Apple keeps putting fancier cameras into every iPhone even though I'm pretty sure a good chunk of customers don't need a fancy camera. Heck, just getting a phone that fits in my hand was a struggle because buyers somehow got convinced that bigger phone = better phone and now most smartphones on the market are just half-size tablets.

That trend at least seems to be somewhat reversing though.

The trend is sadly not reversing fast enough. Apple already discontinued their line of slightly too big phones (mini series), and now they only sell oversized phablets. I might not have viable iOS-based hardware options when I upgrade in 2-3 years, and I'm not comfortable switching to an operating system made by an adtech company. I do hope they go back to smaller sizes before then. Kind of baffling to me how Apple otherwise puts a lot of effort into accessibility, but their main line of phones are awkward and uncomfortable to hold even for a fully able-bodied person with average size hands.

I think by “buyer” they mean the phone manufacturer buying parts

I agree, but consider that the buyer must also consider what the end-customer cares about. The buyer is not going to pay the chip manufacturer extra for mainlined (or at least open source) drivers unless their end-customers are asking for that (since those costs will be passed on to the customer). And outside of niche products like Librem's, the vast majority of customers don't even know about chipset drivers, let alone care.

Because you don't have much choice, and each choice has trade offs. If you pick the part from vendor A, you get the mainlined driver, but maybe you get slower performance, or higher power consumption, or a larger component footprint that doesn't work with your form factor.

And most vendors are like vendor B because they're leading the pack in terms of performance, power consumption, and die size (among other things) and have the market power to avoid having to do everything their customers want them to do.

Still, some headway has been made: Google and Samsung have been gradually getting some manufacturers (mainly Qualcomm) to support their chips for longer. It's been a slow process, though.

As for mainlining: it's a long, difficult process, and the vendor-B types just don't care, and mostly don't need to care.