linux-kernel - Re: [PATCH v2 2/2] RISC-V: defconfig: Enable Goldfish RTC driver

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Message-ID: <alpine.DEB.2.21.9999.1910231105170.16536@viisi.sifive.com>
Date:   Wed, 23 Oct 2019 11:20:43 -0700 (PDT)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Alistair Francis <Alistair.Francis@....com>
cc:     "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Atish Patra <Atish.Patra@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "rkir@...gle.com" <rkir@...gle.com>,
        Anup Patel <Anup.Patel@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "anup@...infault.org" <anup@...infault.org>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>
Subject: Re: [PATCH v2 2/2] RISC-V: defconfig: Enable Goldfish RTC driver

On Wed, 23 Oct 2019, Alistair Francis wrote:

> On Tue, 2019-10-22 at 18:06 -0700, Paul Walmsley wrote:
> > On Tue, 22 Oct 2019, Alistair Francis wrote:
> > 
> > > I think it makese sense for this to go into Linux first.
> > > 
> > > The QEMU patches are going to be accepted, just some nit picking to 
> > > do first :)
> > > 
> > > After that we have to wait for a PR and then a QEMU release until 
> > > most people will see the change in QEMU. In that time Linux 5.4 will 
> > > be released, if this can make it into 5.4 then everyone using 5.4 
> > > will get the new RTC as soon as they upgrade QEMU (QEMU provides the 
> > > device tree). If this has to wait until QEMU has support then it 
> > > won't be supported for users until even later.
> > > 
> > > Users are generally slow to update kernels (buildroot is still using 
> > > 5.1 by default for example) so the sooner changes like this go in 
> > > the better.
> > 
> > The defconfigs are really just for kernel developers.  We expect users 
> > to define their own Kconfigs for their own needs.
> 
> From experience most people use the defconfig, at least as a starting
> point.

We'll definitely add it to the defconfigs, but I think it makes sense to 
do that once the patches hit the QEMU master branch.  (No need to wait for 
a QEMU release.)

That roughly matches what I understand the Linux kernel's approach is to 
adding hardware support: no point in adding hardware support until it 
looks likely that it will actually exist.  Otherwise it just adds churn 
and maintenance burden.

> I was under the impression that everyone was on board with this going
> in. In QEMU land it doesn't make sense to add it if the kernel isn't
> going to, so we need to be on the same page here.

Whatever RTC gets added into QEMU, we'll take defconfig patches for.  I 
don't care which one it is.  Based on the patches that hit the kernel 
lists, it initially looked like the Goldfish RTC was more complicated than 
it needed to be; but it turned out I just didn't look deeply enough.

> From the other discussions it looks like you are happy with this change
> overall right?

Yes


- Paul