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From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Lee Jones <lee.jones@linaro.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
	Will McVicker <willmcvicker@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	"Cc: Android Kernel" <kernel-team@android.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
	Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v1 2/4] soc: samsung: change SOC_SAMSUNG default config logic
Date: Thu, 23 Sep 2021 20:05:41 +0200	[thread overview]
Message-ID: <CAMuHMdVj4nEVUN=+gmknKvGSkZtOyE3hXcZ5cim+iJz491S-gw@mail.gmail.com> (raw)
In-Reply-To: <CAMuHMdUaHPoCDnu3sD7WOnvyaMp5qNjuRGaFxEDQp1ZoFkcrvg@mail.gmail.com>

On Thu, Sep 23, 2021 at 6:19 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> On Thu, Sep 23, 2021 at 3:42 PM Lee Jones <lee.jones@linaro.org> wrote:
> > On Thu, 23 Sep 2021, Krzysztof Kozlowski wrote:
> > > On 23/09/2021 14:39, Lee Jones wrote:
> > > > As I've explained before, the trigger for all of this was
> > > > SERIAL_SAMSUNG which is required for early console on supported
> > > > Samsung platforms i.e. this symbol *has* to be built-in.
> > >
> > > Actually SERIAL_SAMSUNG does not have to be built-in. It is necessary
> > > for built-in only for debugging or development, not for real products.
> >
> > Right.  And in the early stages, GKI is used for early (non-released)
> > H/W (this is also the part of the reason these differences can't be
> > upstreamed early/now/yet) and sometimes changes break things requiring
> > low-level debugging techniques to solve (inc. early console).
> >
> > > Unlike other drivers which have to be built-in, e.g. clocks or pinctrl,
> > > or heavily tested whether setup from initrd works. Plus not breaking
> > > distros who like to have everything as module (solution from Geert?)...
> >
> > We don't know which drivers *need* to be built-in yet.
> >
> > Clocks is probably not a good example even, since the power-on default
> > is most likely all-on, which is fine.  Pinctrl remains to be seen.
>
> Clocks is an excellent example: if a clock is missing, the driver
> will fail to probe (unless the clock is considered optional by
> the driver), regardless of the power-on or boot loader defaults.
> With fw_devlinks=on (which is the default now, and developed by a
> Google engineer (GKI or another division?)), the driver won't even
> get to the probing point.
>
> Pinctrl is different, as unless I'm mistaken, drivers will still
> probe if the pin control driver is missing, so they will work if the
> power-on or boot loader defaults of pin control are fine.

In addition, relying on implicit power-on or boot loader state comes
with its own set of pitfalls, which may break other use cases.
On a heavily power-managed mobile device, clocks and/or power domains
can be turned off, so a kernel launched from kexec or kdump may start
in a state not adhering to these implicit dependencies.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

  reply	other threads:[~2021-09-23 18:05 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-20 19:03 [PATCH v1 0/4] arm64: Kconfig: Update ARCH_EXYNOS select configs Will McVicker
2021-09-20 19:03 ` [PATCH v1 1/4] clk: samsung: change COMMON_CLK_SAMSUNG default config logic Will McVicker
2021-09-21  7:29   ` Krzysztof Kozlowski
2021-09-21  7:50     ` Geert Uytterhoeven
2021-09-21  8:35       ` Krzysztof Kozlowski
2021-09-21 17:58         ` Will McVicker
2021-09-21 18:04           ` Krzysztof Kozlowski
2021-09-23 12:57             ` Lee Jones
2021-09-23 13:27               ` Krzysztof Kozlowski
2021-09-23 14:18                 ` Lee Jones
2021-09-23 16:27                   ` Krzysztof Kozlowski
2021-09-23 16:30                     ` Krzysztof Kozlowski
2021-09-20 19:03 ` [PATCH v1 2/4] soc: samsung: change SOC_SAMSUNG " Will McVicker
2021-09-20 20:57   ` Will McVicker
2021-09-21  7:23   ` Krzysztof Kozlowski
2021-09-21  8:19     ` Lee Jones
2021-09-21 17:45       ` Will McVicker
2021-09-21 18:20         ` Krzysztof Kozlowski
2021-09-23 12:39           ` Lee Jones
2021-09-23 12:57             ` Krzysztof Kozlowski
2021-09-23 13:41               ` Lee Jones
2021-09-23 16:19                 ` Geert Uytterhoeven
2021-09-23 18:05                   ` Geert Uytterhoeven [this message]
2021-09-20 19:03 ` [PATCH v1 3/4] pinctrl: samsung: change PINCTRL_EXYNOS " Will McVicker
2021-09-21  7:27   ` Krzysztof Kozlowski
2021-09-21  8:18     ` Lee Jones
2021-09-23 21:52   ` Linus Walleij
2021-09-21  7:08 ` [PATCH v1 0/4] arm64: Kconfig: Update ARCH_EXYNOS select configs Lee Jones
2021-09-21  7:19 ` Krzysztof Kozlowski
2021-09-21  7:22   ` Krzysztof Kozlowski
2021-09-21  8:11   ` Lee Jones
2021-09-21  8:25     ` Krzysztof Kozlowski
2021-09-21  8:41       ` Lee Jones
2021-09-25  2:17       ` Saravana Kannan
2021-09-27  8:08         ` Krzysztof Kozlowski
2021-09-27  8:16           ` Geert Uytterhoeven
2021-09-27 18:07           ` Saravana Kannan
2021-09-27 19:54             ` Geert Uytterhoeven

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