linux-kernel - Re: [PATCH v3] drm/bochs: add edid support.

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Message-ID: <87y3afokav.fsf@intel.com>
Date:   Tue, 30 Oct 2018 11:28:24 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Daniel Vetter <daniel@...ll.ch>, Gerd Hoffmann <kraxel@...hat.com>
Cc:     David Airlie <airlied@...ux.ie>, David Airlie <airlied@...hat.com>,
        open list <linux-kernel@...r.kernel.org>,
        dri-devel@...ts.freedesktop.org,
        "open list\:DRM DRIVER FOR BOCHS VIRTUAL GPU" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH v3] drm/bochs: add edid support.

On Tue, 30 Oct 2018, Daniel Vetter <daniel@...ll.ch> wrote:
> On Mon, Oct 29, 2018 at 09:05:20PM +0100, Gerd Hoffmann wrote:
>> On Mon, Oct 29, 2018 at 07:44:28PM +0200, Jani Nikula wrote:
>> > On Mon, 29 Oct 2018, Gerd Hoffmann <kraxel@...hat.com> wrote:
>> > > Recent qemu (latest master branch, upcoming 3.1 release) got support
>> > > for EDID data.  This patch adds guest driver support.
>> > >
>> > > EDID support in qemu is not (yet) enabled by default, so please use
>> > > 'qemu -device VGA,edid=on' for testing.
>> > 
>> > Any chance of making this use drm_get_edid() (requires an i2c_adapter)
>> > or at least drm_do_get_edid()?
>> 
>> I'll have a look at using drm_do_get_edid().  drm_get_edid() will not
>> fly as there is no i2c adapter in the first place.
>
> Hm, not sure that makes sense. drm_do_get_edid is to handle the real-world
> flakiness of sinks (it's where all the retry logic resides), if you don't
> have a i2c_adapater (because the hw has some magic "give me an edid"
> block). For virtual hw we hopefully don't randomly drop bits on the floor
> between the guest and host. Imo totally fine as-is.
>
> E.g. we also don't feed the VBT edid through drm_do_get_edid either.

But nowadays we do handle the debugfs EDID override and the EDID
firmware loading in drm_do_get_edid(), so using that gives you those
features.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center