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

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Message-ID: <8310417c-bba9-49ed-9049-bee5b23c2e3f@linaro.org>
Date:   Mon, 28 Aug 2023 17:38:17 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Bryan O'Donoghue <bryan.odonoghue@...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 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