linux-kernel - Re: [PATCH v1 7/9] media: verisilicon: Add Rockchip AV1 decoder

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Message-ID: <cb95838c835aa91cd69e7067c8a3b747f89d2e95.camel@collabora.com>
Date:   Fri, 23 Dec 2022 20:15:38 -0300
From:   Daniel Almeida <daniel.almeida@...labora.com>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        Nicolas Dufresne <nicolas@...fresne.ca>,
        ezequiel@...guardiasur.com.ar, p.zabel@...gutronix.de,
        mchehab@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, heiko@...ech.de,
        nicolas.dufresne@...labora.co.uk
Cc:     linux-media@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH v1 7/9] media: verisilicon: Add Rockchip AV1 decoder

> > +	int cur_offset[V4L2_AV1_NUM_REF_FRAMES - 1];
> > +	int cur_roffset[V4L2_AV1_NUM_REF_FRAMES - 1];
> 
> This looks like V4L2_AV1_REFS_PER_FRAME. Daniel, should be remove
> this
> V4L2_AV1_NUM_REF_FRAMES ? Its redundant with
> V4L2_AV1_TOTAL_REFS_PER_FRAME ...

Hi. These are different. NUM_REF_FRAMES is the size of the "DPB" while
TOTAL_REFS_PER_FRAME is the maximum number of references a frame can
use. It just so happens that in AV1 these two are close in absolute
value (i.e. 7 vs 8).

Using VP9 as a comparison, the DPB size is still 8, but REFS_PER_FRAME
is 3 (meaning a frame can specificy LAST, GOLDEN and ALTREF values).

As this is per spec and a mere convenience, I vote for keeping it. 

-- Daniel