linux-kernel - Re: [PATCH v6 1/3] drm/lsdc: add drm driver for loongson display controller

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Date:   Wed, 16 Feb 2022 14:43:34 +0000
From:   Daniel Stone <daniel@...ishbar.org>
To:     Sui Jingfeng <15330273260@....cn>
Cc:     Maxime Ripard <maxime@...no.tech>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        suijingfeng <suijingfeng@...ngson.cn>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org,
        Randy Dunlap <rdunlap@...radead.org>,
        Roland Scheidegger <sroland@...are.com>,
        linux-mips@...r.kernel.org, Krzysztof Kozlowski <krzk@...nel.org>,
        linux-kernel@...r.kernel.org,
        Andrey Zhizhikin <andrey.zhizhikin@...ca-geosystems.com>,
        Rob Herring <robh+dt@...nel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v6 1/3] drm/lsdc: add drm driver for loongson display controller

On Wed, 16 Feb 2022 at 14:13, Sui Jingfeng <15330273260@....cn> wrote:
> On 2022/2/16 21:46, Daniel Stone wrote:
> > Other systems have this limitation, and Mesa's 'kmsro' concept makes
> > this work transparently, as long as your driver can export dmabufs
> > when running in 'VRAM' mode.
>
> When using vram helper based driver, the framebuffer  is locate at video
> ram. the backing memory fb is manage by TTM.
>
> while bo of etnaviv is locate at system ram. Currently i can't figure
> out how does the buffer going to be shared.

kmsro will allocate from the KMS device (usually using dumb buffers),
export that BO as a dmabuf, then import into etnaviv. etnaviv already
uses this for imx-drm.

Cheers,
Daniel