linux-kernel - Re: [PATCH v3 7/8] watchdog: max77714: add driver for the watchdog in the MAX77714 PMIC

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Date:   Fri, 12 Nov 2021 11:23:39 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Luca Ceresoli <luca@...aceresoli.net>,
        linux-kernel@...r.kernel.org
Cc:     Lee Jones <lee.jones@...aro.org>, Rob Herring <robh+dt@...nel.org>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        devicetree@...r.kernel.org, linux-rtc@...r.kernel.org,
        linux-watchdog@...r.kernel.org,
        Chiwoong Byun <woong.byun@...sung.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v3 7/8] watchdog: max77714: add driver for the watchdog in
 the MAX77714 PMIC

On 11/12/21 8:07 AM, Krzysztof Kozlowski wrote:
> On 12/11/2021 17:02, Luca Ceresoli wrote:
>> Hi Guenter,
>>
>> On 12/11/21 15:57, Guenter Roeck wrote:
>>> On 11/11/21 2:58 PM, Luca Ceresoli wrote:
>>>> Add a simple driver to support the watchdog embedded in the Maxim
>>>> MAX77714
>>>> PMIC.
>>>>
>>>> Signed-off-by: Luca Ceresoli <luca@...aceresoli.net>
>>>>
>>>
>>> I just realized that this is effectively a rewrite of
>>> drivers/watchdog/max77620_wdt.c.
>>> The only difference I can see is is the register offsets (0x91 and 0x92
>>> vs. 1 and 2) and some implementation details. Please add support for this
>>> watchdog to the other driver or provide a _really_ good reason why that
>>> is not possible.
>>
>> I initially started developing MAX77714 watchdog support as an addition
>> to max77620_wdt.c as the procedures look identical at least for the
>> basic features.
>>
>> But the register content seems completely different. Here are the notes
>> I took at that time:
>>
>> -------------------------8<-------------------------
>>
>> MAX77620 has reg ONOFFCNFG1  at 0x41, ONOFFCNFG2  at 0x42.
>> MAX77714 has reg CNFG1_ONOFF at 0x93, CNFG2_ONOFF at 0x94.
>> OK, we can handle this with a register indirection table, indexed by
>> chip model.
>>
>> MAX77620 has MAX77620_REG_FPS_CFG0 register.
>> On MAX77714 I was unable to find any such register (I haven't looked at
>> FPS in detail though).
>> OK, we can handle this with some if()s or entirely disable PM on the
>> 77714 until anybody cares.
>>
>> MAX77620 ONOFFCNFG1  has SFT_RST in bit 7.
>> MAX77714 CNFG1_ONOFF has SFT_RST is bit 6.
>> Uhm, should we have a _bit_ indirection table in addition to the
>> _register_ indirection table?
>>
>> MAX77620 ONOFFCNFG2  bit 5 is SLP_LPM_MSK, involved in FPS.
>> MAX77620 ONOFFCNFG2  bit 6 is WD_RTS_WK, configures the watchdog timer.
>> MAX77714 CNFG2_ONOFF bit 5 is WD_RTS_WK, configures the watchdog timer.
>> On MAX77714 I haven't found SLP_LPM_MSK.
>>
>> MAX77620 has 6 CID registers with "ES version" in CID5.
>> MAX77714 has 5 CID registers with "DEVICE id" in CID3.
>> CID registers would be useful to get the chip model directly from the
>> chip, if only they had the same structure.
>>
>> Almost all of the registers I have been looking into have similar
>> differences.
>>
>> -------------------------8<-------------------------
>>
>> When I started adding indirection tables the driver started growing
>> bigger and uglier, and that little simple driver started being big and
>> complex. So I opted to add a new driver.
>>
> 
> The register offset differences are trivial and we do it in several
> drivers. Also in rtc-max77686 used by you here.
> Lack of features as well - just have a variant/driver data which defines
> certain features (true/false) or quirk bits (see s3c2410_wdt).
> 
> The second driver - s3c2410_wdt - also customizes the bits.
> 
> Therefore if the generic device operating configuration is similar (same
> generic control flow) and differences are in bits and offsets, then it
> should be one driver.
> 

Exactly.

Thanks,
Guenter