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Subject: Re: [PATCH 12/12] arm64: dts: exynos: Add Exynos850 SoC support
From:   Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
To:     Sam Protsenko <semen.protsenko@linaro.org>,
        =?UTF-8?Q?Pawe=c5=82_Chmiel?= <pawel.mikolaj.chmiel@gmail.com>
Cc:     Sylwester Nawrocki <s.nawrocki@samsung.com>,
        Chanwoo Choi <cw00.choi@samsung.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Tomasz Figa <tomasz.figa@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Jiri Slaby <jirislaby@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Charles Keepax <ckeepax@opensource.wolfsonmicro.com>,
        Ryu Euiyoul <ryu.real@samsung.com>,
        Tom Gall <tom.gall@linaro.org>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        John Stultz <john.stultz@linaro.org>,
        Amit Pundir <amit.pundir@linaro.org>,
        devicetree <devicetree@vger.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
        linux-clk <linux-clk@vger.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Samsung SOC <linux-samsung-soc@vger.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>
References: <20210730144922.29111-1-semen.protsenko@linaro.org>
 <20210730144922.29111-13-semen.protsenko@linaro.org>
 <455cfb5e-dff7-a5c0-3875-49abe3e900f3@canonical.com>
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 <68734f6c-fc76-595c-8d34-8924dbbbb845@canonical.com>
 <CAPLW+4n_JKj5xeBHXONcv__vyAFvx3fhXoxJa17NTHK1RSJFJw@mail.gmail.com>
 <b753796c-2ce6-4166-7c20-289e950237ad@canonical.com>
Message-ID: <bb08f7a4-1da9-fb20-f091-6a3c37a1f898@canonical.com>
Date:   Fri, 6 Aug 2021 14:48:11 +0200
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On 06/08/2021 14:32, Krzysztof Kozlowski wrote:
> On 06/08/2021 14:07, Sam Protsenko wrote:
>> On Fri, 6 Aug 2021 at 10:49, Krzysztof Kozlowski
>> <krzysztof.kozlowski@canonical.com> wrote:
>>>
>>> On 06/08/2021 01:06, Sam Protsenko wrote:
>>>> On Sat, 31 Jul 2021 at 12:03, Krzysztof Kozlowski
>>>> <krzysztof.kozlowski@canonical.com> wrote:
>>>>
>>>>>>
>>>>>> This patch adds minimal SoC support. Particular board device tree files
>>>>>> can include exynos850.dtsi file to get SoC related nodes, and then
>>>>>> reference those nodes further as needed.
>>>>>>
>>>>>> Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
>>>>>> ---
>>>>>>  .../boot/dts/exynos/exynos850-pinctrl.dtsi    | 782 ++++++++++++++++++
>>>>>>  arch/arm64/boot/dts/exynos/exynos850-usi.dtsi |  30 +
>>>>>>  arch/arm64/boot/dts/exynos/exynos850.dtsi     | 245 ++++++
>>>>>
>>>>> Not buildable. Missing Makefile, missing DTS. Please submit with initial
>>>>> DTS, otherwise no one is able to verify it even compiles.
>>>>>
>>>>
>>>> This device is not available for purchase yet. I'll send the patch for
>>>> board dts once it's announced. I can do all the testing for now, if
>>>> you have any specific requests. Would it be possible for us to review
>>>> and apply only SoC support for now? Will send v2 soon...
>>>
>>> What you propose is equal to adding a driver (C source code) without
>>> ability to compile it. What's the point of having it in the kernel? It's
>>> unverifiable, unbuildable and unusable.
>>>
>>
>> Yes, I understand. That's adding code with no users, and it's not a
>> good practice.
>>
>>> We can review the DTSI however merging has to be with a DTS. Usually the
>>> SoC vendor adds first an evalkit (e.g. SMDK board). Maybe you have one
>>> for Exynos850? Otherwise if you cannot disclose the actual board, the
>>> DTSI will have to wait. You can submit drivers, though.
>>>
>>
>> Sure, let's go this way. I'll send v2 soon. Improving patches and
>> having Reviewed-by tag for those would good enough for me at this
>> point. I'll continue to prepare another Exynos850 related patches
>> until the actual board is announced, like proper clock driver, reset,
>> MMC, etc. Is it ok if I send those for a review too (so I can fix all
>> issues ahead)?
> 
> Sure, prepare all necessary drivers earlier. I suspect clocks will be a
> real pain because of significant changes modeled in vendor kernel. I
> remember Paweł Chmiel (+Cc) was doing something for these:
> https://github.com/PabloPL/linux/tree/exynos7420
> 
> I mentioned before - you should also modify the chipid driver. Check
> also other drivers in drivers/soc/samsung, although some are needed only
> for suspend&resume.
> 

You can also take a look at Exynos8895 efforts:
https://github.com/ivoszbg/linux/commits/for-upstream/exynos8895

Since knowledge, datasheets and efforts are quite spread all over, I
keep track of some work here:
https://exynos.wiki.kernel.org/community


Best regards,
Krzysztof