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Subject: Re: [PATCH] usb: dwc3: make USB_DWC3_EXYNOS independent
From:   Krzysztof Kozlowski <krzk@kernel.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>
Cc:     Guenter Roeck <linux@roeck-us.net>,
        taehyun cho <taehyun.cho@samsung.com>,
        Felipe Balbi <balbi@kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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Message-ID: <159d72a6-e200-913f-6ec1-4668db797a04@kernel.org>
Date:   Wed, 3 Mar 2021 17:50:31 +0100
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On 03/03/2021 17:49, Krzysztof Kozlowski wrote:
>> And "new drivers" are almost always not really "new" as everyone uses
>> much the same IP blocks.  As proof of this patch where the DWC3 IP block
>> is being used by multiple SoC vendors.  To handle that, you split out
>> the SoC-specific portions into sub-drivers, so that you can build a
>> single image of the driver that works on multiple platforms.  Nothing
>> new, we've been doing this for years, it's just that out-of-mainline SoC
>> trees that think they can touch "core IP block code" break this all the
>> time, which is what I am pushing back on.
> 
> I am perfectly fine with (and like it!) putting dwc3 exynos back into 
> base/main dwc3  and getting rid of USB_DWC3_EXYNOS entirely. But this 
> was not part of this patch...
> 
>>
>> Anyway, this is just me as a driver subsystem maintainer being grumpy to
>> see ARCH_ dependancies on tiny little things like SoC-portions for
>> generic IP drivers.  Or on individual drivers (i.e. Samsung serial port
>> driver), where they don't belong at all.
> 
> At least with Samsung serial driver we see adding new SoC - Apple M1.
> 
> Here, the guys in Samsung want to tweak several kernel parts to work 
> with their out-of-tree code without contributing this code back. It's 
> not a community-friendly approach. The upstream kernel should be tweaked 
> to the out-of-tree unknown, hidden and uncontrollable code.

Eh, obviously I wanted to say:
The upstream kernel should *not* be tweaked to the out-of-tree unknown, 
hidden and uncontrollable code.

> 
> Instead I expect from Samsung to contribute the basic Exynos9 support to 
> the upstream.

Best regards,
Krzysztof