linux-kernel - Re: [PATCH v2 1/2] drm/file: Rehabilitate the firstopen hook for non-legacy drivers

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Message-ID: <CAPj87rMmW_7Kiy==ZxvvmHXhQLWC+F=uxed442HpMMZr=MwjRA@mail.gmail.com>
Date:   Fri, 29 Mar 2019 09:09:46 +0000
From:   Daniel Stone <daniel@...ishbar.org>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Eric Anholt <eric@...olt.net>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Eben Upton <eben@...pberrypi.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 1/2] drm/file: Rehabilitate the firstopen hook for
 non-legacy drivers

Hi,

On Thu, 28 Mar 2019 at 18:53, Daniel Vetter <daniel@...ll.ch> wrote:
> On Thu, Mar 21, 2019 at 04:27:06PM +0100, Paul Kocialkowski wrote:
> > I don't see other options either, and using firstclose/lastopen feels
> > overall more readable in the driver code.
> >
> > I'm not sure there is such a big overhead associated with allocating
> > the binner BO (it seems that the current implementation tries to alloc
> > until the specific memory constraints for the buffer are met, so
> > perhaps that can take time). But if there is, I suppose it's best to
> > have that when starting up rather than delaying the first render
> > operation.
>
> I'm not entirely buying the "we don't need this for fbcon only" argument -
> there's plenty of dumb kms clients too (boot splash and whatever else
> there might be). If you don't want to keep this around I think allocating
> on first non-dumb bo allocation and dropping it when the last such fd
> closes sounds like a much better idea. Needs a bit more state, you need to
> track per drm_file whether you've already allocated a non-dumb bo, and a
> drm_device refcount, but that's not much. Firstopen feels like the wrong
> thing.
>
> Another option would be first_renderopen or something like that, except
> you can also render on the legacy node and I'm not sure how much there's a
> demand for this in other drivers. In the end you have open/close
> callbacks, you can do all the driver specific things you want to do in
> there.

I'd like to avoid doing it in open where possible, since that hurts
device enumeration from userspace.

Cheers,
Daniel