linux-kernel - Re: [PATCH v1 6/6] i2c: npcm: Support NPCM845

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Date:   Tue, 8 Feb 2022 08:59:05 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Tali Perry <tali.perry1@...il.com>
Cc:     Jonathan Neuschäfer <j.neuschaefer@....net>,
        Tyrone Ting <warp5tw@...il.com>, avifishman70@...il.com,
        Tomer Maimon <tmaimon77@...il.com>,
        Patrick Venture <venture@...gle.com>,
        Nancy Yuen <yuenn@...gle.com>,
        Benjamin Fair <benjaminfair@...gle.com>,
        Rob Herring <robh+dt@...nel.org>, semen.protsenko@...aro.org,
        yangyicong@...ilicon.com, Wolfram Sang <wsa@...nel.org>,
        jie.deng@...el.com, sven@...npeter.dev, bence98@....bme.hu,
        lukas.bulwahn@...il.com, arnd@...db.de, olof@...om.net,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Tali Perry <tali.perry@...oton.com>,
        Avi Fishman <Avi.Fishman@...oton.com>,
        tomer.maimon@...oton.com, KWLIU@...oton.com, JJLIU0@...oton.com,
        kfting@...oton.com, devicetree <devicetree@...r.kernel.org>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Linux I2C <linux-i2c@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 6/6] i2c: npcm: Support NPCM845

On 08/02/2022 08:14, Tali Perry wrote:
>> -----Original Message-----
>> From: Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
>> Sent: Monday, February 7, 2022 5:27 PM
>> To: Jonathan Neuschäfer <j.neuschaefer@....net>; Tyrone Ting <warp5tw@...il.com>
>> Cc: avifishman70@...il.com; tmaimon77@...il.com; tali.perry1@...il.com; venture@...gle.com; yuenn@...gle.com; benjaminfair@...gle.com; robh+dt@...nel.org; semen.protsenko@...aro.org; yangyicong@...ilicon.com; wsa@...nel.org; jie.deng@...el.com; sven@...npeter.dev; bence98@....bme.hu; lukas.bulwahn@...il.com; arnd@...db.de; olof@...om.net; andriy.shevchenko@...ux.intel.com; IS20 Tali Perry <tali.perry@...oton.com>; IS20 Avi Fishman <Avi.Fishman@...oton.com>; IS20 Tomer Maimon <tomer.maimon@...oton.com>; CS20 KWLiu <KWLIU@...oton.com>; CS20 JJLiu0 <JJLIU0@...oton.com>; CS20 KFTing <KFTING@...oton.com>; devicetree@...r.kernel.org; openbmc@...ts.ozlabs.org; linux-i2c@...r.kernel.org; linux-kernel@...r.kernel.org
>> Subject: Re: [PATCH v1 6/6] i2c: npcm: Support NPCM845
>>
>> On 07/02/2022 13:00, Jonathan Neuschäfer wrote:
>>> Hello,
>>>
>>> On Mon, Feb 07, 2022 at 02:33:38PM +0800, Tyrone Ting wrote:
>>>> From: Tyrone Ting <kfting@...oton.com>
>>>>
>>>> NPCM8XX uses a similar i2c module as NPCM7XX.
>>>> The only difference is that the internal HW FIFO is larger.
>>>>
>>>> Related Makefile and Kconfig files are modified to support as well.
>>>>
>>>> Fixes: 56a1485b102e ("i2c: npcm7xx: Add Nuvoton NPCM I2C controller
>>>> driver")
>>>
>>> It's not really a bug fix, but rather an additional feature.
>>> Therefore, I suggest removing the Fixes tag from this patch.
>>>
>>>> Signed-off-by: Tyrone Ting <kfting@...oton.com>
>>>> Signed-off-by: Tali Perry <tali.perry1@...il.com>
>>>> ---
>>> [...]
>>>>  /* init register and default value required to enable module */
>>>>  #define NPCM_I2CSEGCTL 0xE4
>>>> +#ifdef CONFIG_ARCH_NPCM7XX
>>>>  #define NPCM_I2CSEGCTL_INIT_VAL 0x0333F000
>>>> +#else
>>>> +#define NPCM_I2CSEGCTL_INIT_VAL 0x9333F000
>>>> +#endif
>>>
>>> This is going to cause problems when someone tries to compile a kernel
>>> that runs on both NPCM7xx and NPCM8xx (because the driver will then
>>> only work on NPCM7xx).
>>
>> Yes, good catch.
>>
>> The NPCM7XX is multiplatform, I guess NPCM8xx will be as well, so this looks like an invalid code. How such code is supposed to work on multiplatform kernel?
>>
> 
> NPCM7xx and NPCM8xx are very different devices.
> They share same driver sources for some of the modules but it's not ABI.
> Users cannot compile a single kernel with two separate DTS.
> In case of the i2c controller, the npcm7xx has a 16 byte HW FIFO,
> and the NPCM8xx has 32 bytes HW FIFO.
> This also means that registers fields are slightly different.
> For init data we can move it to the DTS, but register field sizes
> can't be handled with this approach.
> 

What do you mean they cannot compile a kernel with different DTS? Of
course they can - when we talk about multiplatform sub-architectures!
Maybe there is something specific in NPCMxxx which stops it but then it
should not be marked multiplatform.


Best regards,
Krzysztof