linux-kernel - RE: [EXT] Re: [PATCH] media: videobuf2-dma-sg: limit the sg segment size

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Message-ID: <DB9PR04MB9284404C1E1F1300EEF5A70487F1A@DB9PR04MB9284.eurprd04.prod.outlook.com>
Date:   Tue, 12 Sep 2023 07:43:25 +0000
From:   Hui Fang <hui.fang@....com>
To:     Tomasz Figa <tfiga@...omium.org>
CC:     Anle Pan <anle.pan@....com>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jindong Yue <jindong.yue@....com>,
        Xuegang Liu <xuegang.liu@....com>, Xu Yang <xu.yang_2@....com>
Subject: RE: [EXT] Re: [PATCH] media: videobuf2-dma-sg: limit the sg segment
 size

On Tue, Sep 12, 2023 at 4:11 PM Tomasz Figa <tfiga@...omium.org> wrote:
> Is your DMA device restricted only to the bottom-most 4 GB (32-bit DMA
> address)? If yes, would it make sense to also allocate from that area rather
> than bouncing the memory?

The DMA device use 32-bit DMA address.
From user space, can't control the v4l2 buffer address, may still change the
code of vb2_dma_sg_alloc().

BRs,
Fang Hui