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

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Message-ID: <086655b0-b9d2-30ed-1496-47cdc6346003@canonical.com>
Date:   Mon, 7 Feb 2022 16:26:30 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
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,
        tali.perry@...oton.com, Avi.Fishman@...oton.com,
        tomer.maimon@...oton.com, KWLIU@...oton.com, JJLIU0@...oton.com,
        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?

> 
> And every time another platform is added, this approach will make the
> code less readable.
> 
> A more future-proof approach is probably to have a struct with chip-
> specific data (such as the I2CSECCTL initialization value), which is
> then selected via the .data field in of_device_id.


Best regards,
Krzysztof