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From:   Daniel Stone <daniel@fooishbar.org>
Date:   Wed, 16 Feb 2022 14:43:34 +0000
Message-ID: <CAPj87rOY0j7p5fduA+p-kT8HP7kc8f4j2Q=FkGutPPPvmV7zqQ@mail.gmail.com>
Subject: Re: [PATCH v6 1/3] drm/lsdc: add drm driver for loongson display controller
To:     Sui Jingfeng <15330273260@189.cn>
Cc:     Maxime Ripard <maxime@cerno.tech>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        suijingfeng <suijingfeng@loongson.cn>,
        David Airlie <airlied@linux.ie>,
        dri-devel@lists.freedesktop.org,
        Randy Dunlap <rdunlap@infradead.org>,
        Roland Scheidegger <sroland@vmware.com>,
        linux-mips@vger.kernel.org, Krzysztof Kozlowski <krzk@kernel.org>,
        linux-kernel@vger.kernel.org,
        Andrey Zhizhikin <andrey.zhizhikin@leica-geosystems.com>,
        Rob Herring <robh+dt@kernel.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Sam Ravnborg <sam@ravnborg.org>
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On Wed, 16 Feb 2022 at 14:13, Sui Jingfeng <15330273260@189.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