linux-kernel - Re: [RESEND PATCH v6 17/17] media: qcom: camss: Comment CSID dt

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Message-ID: <d799f653-e00c-43be-9487-381a8ef4c849@linaro.org>
Date:   Wed, 27 Sep 2023 13:03:46 +0100
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Hans Verkuil <hverkuil@...all.nl>, linux-arm-msm@...r.kernel.org,
        linux-media@...r.kernel.org, laurent.pinchart@...asonboard.com,
        rfoss@...nel.org, todor.too@...il.com, agross@...nel.org,
        andersson@...nel.org, konrad.dybcio@...aro.org, mchehab@...nel.org,
        sakari.ailus@...ux.intel.com, andrey.konovalov@...aro.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v6 17/17] media: qcom: camss: Comment CSID dt_id
 field

On 27/09/2023 12:42, Hans Verkuil wrote:
>> +		/*
>> +		 * DT_ID is a two bit bitfield that is concatenated with
>> +		 * the four least significant bits of the six bit VC
>> +		 * bitfield to generate an internal CID value.
>> +		 *
>> +		 * CSID_RDI_CFG0(vc)
>> +		 * DT_ID : 28:27
>> +		 * VC    : 26:22
> This is 5 bits, not 6 bits as the comment above says. Which is right?

Yes you're right I had "DT" which is six bits in my head when I wrote 
this. The VC bitfield is five.

> 
>> +		 * DT    : 21:16
>> +		 *
>> +		 * CID   : VC 3:0 << 2 | DT_ID 1:0
>> +		 */
>>   		u8 dt_id = vc;
> So if dt_id is 2 bits, and vc can be more than 2 bits in the future,
> shouldn't this read "vc & 3"?

Hmm...

val |= dt_id << RDI_CFG0_DT_ID;

yes that would overrun otherwise.

---
bod