linux-kernel - Re: [PATCH v3 1/3] input: pm8xxx-vib: refactor to easily support new SPMI vibrator

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Date:   Thu, 27 Jul 2023 15:43:51 +0800
From:   Fenglin Wu <quic_fenglinw@...cinc.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <robh+dt@...nel.org>,
        <agross@...nel.org>, <andersson@...nel.org>,
        <dmitry.baryshkov@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        <linux-input@...r.kernel.org>
CC:     <quic_collinsd@...cinc.com>, <quic_subbaram@...cinc.com>,
        <quic_kamalw@...cinc.com>, <jestar@....qualcomm.com>
Subject: Re: [PATCH v3 1/3] input: pm8xxx-vib: refactor to easily support new
 SPMI vibrator



On 7/27/2023 3:07 PM, Krzysztof Kozlowski wrote:
> On 25/07/2023 08:16, Fenglin Wu wrote:
>>>>    
>>>> -static const struct pm8xxx_regs pm8058_regs = {
>>>> -	.drv_addr = 0x4A,
>>>> -	.drv_mask = 0xf8,
>>>> -	.drv_shift = 3,
>>>> -	.drv_en_manual_mask = 0xfc,
>>>> +static struct reg_field ssbi_vib_regs[VIB_MAX_REG] = {
>>>
>>> Change from const to non-const is wrong. How do you support multiple
>>> devices? No, this is way too fragile now.
>>>
>>
>> The register definition is no longer used as the match data, hw_type is
>> used.
>>
>> The last suggestion was getting the register base address from the DT
>> and it has to be added into the offset of SPMI vibrator registers
>> (either in the previous hard-coded format or the later the reg_filed
>> data structure), so it's not appropriated to make it constant.
>>
>> I don't understand this question: "How do you support multiple devices?"
>> For SSBI vibrator, since all the registers are fixed, and I would assume
>> that there is no chance to support multiple vibrator devices on the same
>> SSBI bus. If they are not on the same bus, the regmap device will be
>> different while the registers definition is the same, and we are still
>> able to support multiple devices, right?
> 
> No, you have static memory. One device probes and changes static memory
> to reg+=base1. Second device probes and changes the same to reg+=base2.

Thanks, got it.  I can update it with following 2 options:

1) keep the register definition in 'reg_filed' data structure and make 
it constant, copy it to a dynamically allocated memory before adding the 
'reg_base' to the '.reg' variable.

2) Define the register offsets as constant data and add the 'reg_base' 
to the 'reg' while using 'regmap_read()'/'regmap_write()' functions.

which one is the preferred way?

> 
>> The similar story for SPMI vibrators and it can support multiple devices
>> if they are located on different SPMI bus, or even if they are on the
>> same SPMI bus but just having different SID or PID.
> 
> Sorry, such code cannot go in. These must stay const and you must write
> driver without any static allocations or singleton-like patterns.
> 
> 
> Best regards,
> Krzysztof
>