Re: [PULL] drm-misc-next

From: Sean Paul <sean@poorly.run>
To: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Wen He <wen.he_1@nxp.com>,
	"DRM maintainer tools announcements, discussion,
	and development" <dim-tools@lists.freedesktop.org>,
	Jonas Karlman <jonas@kwiboo.se>,
	Ezequiel Garcia <ezequiel@collabora.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Steven Price <steven.price@arm.com>,
	Oleg Vasilev <omrigann@gmail.com>,
	Gerd Hoffmann <kraxel@redhat.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Robert Chiras <robert.chiras@nxp.com>,
	Jean-Jacques Hiblot <jjhiblot@ti.com>,
	Lowry Li <Lowry.Li@arm.com>, Sam Ravnborg <sam@ravnborg.org>,
	Qiang Yu <yuq825@gmail.com>
Subject: Re: [PULL] drm-misc-next
Date: Mon, 21 Oct 2019 11:48:42 -0400	[thread overview]
Message-ID: <CAMavQK+vNihFv_LKPqpUgBwXh_LCQ8=g=_zyTDe08+pKiVTOGw@mail.gmail.com> (raw)
In-Reply-To: <6dd06a02-b28f-d6a9-da23-f1eb0ce70fca@ti.com>

On Mon, Oct 21, 2019 at 4:11 AM Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
>
> Hi,
>
> On 18/10/2019 23:11, Sean Paul wrote:
> > On Fri, Oct 18, 2019 at 9:46 AM Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
> >>
> >> Hi Sean,
> >>
> >> On 17/10/2019 22:26, Sean Paul wrote:
> >>
> >>> concern for those. The omap OMAP_BO_MEM_* changes though I don't think have
> >>> really reached non-TI eyes. There's no link in the commit message to a UAPI
> >>> implementation and the only reference I could find is libkmsxx which can set
> >>> them through the python bindings. Since this is TI-specific gunk in TI-specific
> >>> headers I'm inclined to let it pass, but I would have liked to have this
> >>> conversation upfront. I figured I'd call this out so you have final say.
> >>
> >> There was some discussion about that a few years back when I initially
> >> sent the patches, but now that I look, the discussion died before really
> >> even starting.
> >>
> >> This is what I said about userspace implementation:
> >>
> >>> Yes, unfortunately that is not going to happen. I don't see how this
> >>> could be used in a generic system like Weston or X. It's meant for very
> >>> specific use cases, where you know exactly the requirements of your
> >>> application and the capabilities of the whole system, and optimize based
> >>> on that.
> >
> > Thanks for the context, Tomi.
> >
> > Indeed it looks like the discussion died, but Laurent still brought up
> > the u/s requirement and the patch was effectively dead until Daniel or
> > Dave weighed in. I'd expect at least some outreach before pushing the
> > patch directly 2+ years later. Has anything changed since then?
>
> There were new review rounds for the series this summer & autumn, but
> no, nothing else. I haven't specifically pinged anyone about the UAPI
> changes.
>
> This series introduces three new flags to an already existing UAPI, and,
> for whatever reason, this didn't register to me as a new UAPI, even if
> Laurent asked about it some years back.
>
> So, my mistake.
>
> The flags are added in a single patch, so I can easily push a revert for
> that if this patch is not acceptable. The rest of the series is cleanup.
>

I'll wait for Dave or Daniel to weigh in on whether they want to take
this, otherwise I'll revert before sending the next pull and we can
have this conversation on the review.

> >> I know this feature is used by customers, but I don't have access to
> >> their applications.
> >
> > Unfortunately, and as you know, that is insufficient/irrelevant for
> > introducing new UAPI. So the question is if the libkmsxx bindings
> > constitute opensource userspace, it's really thin IMO.
>
> Ok. Well, I know and understand the general rule here. But perhaps I
> haven't taken it as strictly as needed.
>
> I have to say I don't quite understand why this rule would be always
> strictly held, though.
>

It's strictly held because once you start accepting the
harmless/isolated features every driver has, you end up with
untestable bloat sprinkled everywhere.

> These flags, for example, what should we do with them?
> - They provide a proven, real use-case benefit.
> - They are specific to SoCs with OMAP DSS and DMM IPs.
> - They are relatively simple.
> - All the details, including the details about the HW, are public.
> - Using them makes sense only in cases where you are tuning your system
> to your application, and you must know the resource needs of all the
> apps in your system. So they cannot really be used in any generic setup,
> or at least I have no idea how.
>
> Does the history and experience say that such specific case as above
> cases don't really exist, and we can always have a generic UAPI (or, in
> worst case, a device specific UAPI) which can be used from X/Weston/or-such?
>

We don't need generic userspace to be able to make use of it, but at
least some oss project should find it useful. Otherwise why are we
maintaining code that no one in the open source community cares about?
How do we test it when the closed source implementations have been
abandoned?

> Or do things like above exist, but they need to carried in vendors' kernels?

That's really the problem. _Everybody_ has features they would
describe as above, so where do we draw the line?

Sean

>
>   Tomi
>
> --
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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