linux-kernel - Re: [PATCH 2/2] phy: qualcomm: eusb2-repeater: Drop the redundant zeroing

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Date: Fri, 5 Jan 2024 11:09:33 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Abel Vesa <abel.vesa@...aro.org>
Cc: Bjorn Andersson <andersson@...nel.org>, Vinod Koul <vkoul@...nel.org>,
 Kishon Vijay Abraham I <kishon@...nel.org>, linux-arm-msm@...r.kernel.org,
 linux-phy@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] phy: qualcomm: eusb2-repeater: Drop the redundant
 zeroing

On 5.01.2024 10:16, Abel Vesa wrote:
> On 24-01-04 23:50:48, Konrad Dybcio wrote:
>> On 4.01.2024 15:52, Abel Vesa wrote:
>>> The local init_tlb is already zero initialized, so the entire zeroing loop
>>> is useless in this case, since the initial values are copied over anyway,
>>> before being written.
>>>
>>> Fixes: 99a517a582fc ("phy: qualcomm: phy-qcom-eusb2-repeater: Zero out untouched tuning regs")
>>> Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
>>> ---
>>
>> That's another good spot.. partial struct initialization of
>> pm8550b_init_tbl zeroes out the uninitialized fields.
>>
>>
>>>  drivers/phy/qualcomm/phy-qcom-eusb2-repeater.c | 10 ----------
>>>  1 file changed, 10 deletions(-)
>>>
>>> diff --git a/drivers/phy/qualcomm/phy-qcom-eusb2-repeater.c b/drivers/phy/qualcomm/phy-qcom-eusb2-repeater.c
>>> index 5f5862a68b73..3060c0749797 100644
>>> --- a/drivers/phy/qualcomm/phy-qcom-eusb2-repeater.c
>>> +++ b/drivers/phy/qualcomm/phy-qcom-eusb2-repeater.c
>>> @@ -156,16 +156,6 @@ static int eusb2_repeater_init(struct phy *phy)
>>>  
>>>  	regmap_field_update_bits(rptr->regs[F_EN_CTL1], EUSB2_RPTR_EN, EUSB2_RPTR_EN);
>>>  
>>> -	for (i = 0; i < F_NUM_TUNE_FIELDS; i++) {
>>> -		if (init_tbl[i]) {
>>> -			regmap_field_update_bits(rptr->regs[i], init_tbl[i], init_tbl[i]);
>>> -		} else {
>>> -			/* Write 0 if there's no value set */
>>> -			u32 mask = GENMASK(regfields[i].msb, regfields[i].lsb);
>>> -
>>> -			regmap_field_update_bits(rptr->regs[i], mask, 0);
>>> -		}
>>> -	}
>>>  	memcpy(init_tbl, rptr->cfg->init_tbl, sizeof(init_tbl));
>>
>> I think this patchset can be made even better, this memcpy is also
>> useless and we can simply initialize init_tbl=rptr->cfg->init_tbl.
> 
> Actually no. The init_tbl in cfg is a pointer to const. Plus, if you do
> that, you will end up with the same situation like in the other patch,
> as there are some overrides based on DT values below this.

Hm, you're right. Maybe we should simple store *base and stop
modifying these tables then. There's not a whole lot of regmap_rw
calls, so making the first argument "rptr->base + rptr->regs[ASDF]"
shouldn't add much fluff. Then we can make the cfg referernce const.

Konrad

> 
> But now that I've had another look, maybe doing the exact same thing as
> the other patch does (kmemdup) will probably look better anyway,
> specially if we do that on probe.
> 
>>
>> Konrad