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Date:   Wed, 3 Mar 2021 11:38:39 +0100
From:   Krzysztof Kozlowski <krzk@kernel.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Arnd Bergmann <arnd@arndb.de>
Cc:     taehyun cho <taehyun.cho@samsung.com>, balbi@kernel.org,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] usb: dwc3: make USB_DWC3_EXYNOS independent
Message-ID: <20210303103839.it7grj3vtrdmngbd@kozik-lap>
References: <CGME20210303022537epcas2p1b85ab825ceca3a411a177cc1af8a2c7b@epcas2p1.samsung.com>
 <20210303022628.6540-1-taehyun.cho@samsung.com>
 <c9ac155c-56c2-4025-d1ae-d0c6c95533b8@kernel.org>
 <YD9lTjWc25Nn7jAR@kroah.com>
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On Wed, Mar 03, 2021 at 11:30:38AM +0100, Greg Kroah-Hartman wrote:
> On Wed, Mar 03, 2021 at 11:24:01AM +0100, Krzysztof Kozlowski wrote:
> > On 03/03/2021 03:26, taehyun cho wrote:
> > > 'ARCH_EXYNOS' is not suitable for DWC3_EXYNOS config.
> > > 'USB_DWC3_EXYNOS' is glue layer which can be used with
> > > Synopsys DWC3 controller on Exynos SoCs. USB_DWC3_EXYNOS'
> > > can be used from Exynos5 to Exynos9.
> > > 
> > > Signed-off-by: taehyun cho <taehyun.cho@samsung.com>
> > 
> > NACK because you ignored comments from March. Please respond to them instead
> > of resending the same patch.
> > 
> > Anyway, when resending you need to version your patches and explain the
> > differences. Please also Cc reviewers and other maintainers. I pointed out
> > this before:
> > scripts/get_maintainer.pl -f drivers/usb/dwc3/dwc3-exynos.c
> > 
> > The driver - in current form - should not be available for other
> > architectures. It would clutter other platforms and kernel config selection.
> > If you want to change this, you need to provide rationale (usually by adding
> > support to new non-Exynos platform).
> 
> No, these crazy "ARCH_FOO" things need to go away.  For systems that
> want to build "universal" kernels, why are they being forced to enable
> "ARCH_*" just so they can pick specific drivers?  That is not done on
> other architectures, why is ARM64 so "special" in this regard.
> 
> How do you "know" that these cores/devices are tied to specific ARCH_
> platforms?  We don't, so that dependency should not be there.
> 
> Just let any arch pick any driver if it can be built, you never know
> what it might be run on.  Removing ARCH_ dependencies in Kconfig files
> is a good thing, please do not discourage that from happening.

It's getting more generic topic, so let me Cc Arnd and Guenter (I think
once I discussed this with Guenter around watchdog).

This is so far component of a SoC, so it cannot be re-used outside of
SoC. Unless it appears in a new SoC (just like recent re-use of Samsung
serial driver for Apple M1). Because of the architecture, you cannot
build universal kernel without ARCH_EXYNOS. You need it. Otherwise the
kernel won't boot on hardware with DWC Exynos.

Since DWC Exynos won't work without ARCH_EXYNOS - the user will not get
any usable binary - I think all, or almost all, SoC specific drivers are
limited per ARCH. This limits the amount of choices for distro people
and other kernel configuring folks, so they won't have to consider
useless options.

Anyway, that's the convention or consensus so far for entire SoC. If we
want to change it - sure, but let's make it for everyone, not for just
this one USB driver.

Best regards,
Krzysztof