linux-kernel - Re: [PATCH v3 15/15] media: qcom: camss: Comment CSID dt

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Date:   Mon, 28 Aug 2023 16:43:08 +0100
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>, rfoss@...nel.org,
        todor.too@...il.com, agross@...nel.org, andersson@...nel.org,
        mchehab@...nel.org, hverkuil-cisco@...all.nl,
        laurent.pinchart@...asonboard.com, sakari.ailus@...ux.intel.com,
        andrey.konovalov@...aro.org
Cc:     linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 15/15] media: qcom: camss: Comment CSID dt_id field

On 28/08/2023 16:38, Konrad Dybcio wrote:
> On 28.08.2023 17:34, Bryan O'Donoghue wrote:
>> On 26/08/2023 11:18, Konrad Dybcio wrote:
>>>> +        /*
>>>> +         * A value caled 'CID' gets generated internal to CAMSS logic
>>>> +         * which is a concatenation of [vc:6 | dt_id:2] hence we reuse
>>>> +         * the least significant two bits of the VC to 'stuff' the CID value.
>>>> +         */
>>>>            u8 dt_id = vc;
>>> And where are you discarding the non-2-lsb?
>>
>> At the assignment of dt_id
>>
>> vc:6
>> dt_id:2
>>
>> =>
>>
>> cid:8 = [vc:6 | dt_id:2]
>> vc == 00110110
>> cid = [110110 | 10]
>>
>> I have no more information what CID is or how the bitfield is populated than I have already indicated in the comment/commit log.
>>
> OK so you're discarding the 2 lsb of the [vc:6|dt_id:2]
> 
> however
> 
> the way I read the comment would suggest that you're taking
> vc[6:2]
> 
> Konrad

Fair enough, obvs the comment needs work so.

---
bod