Message-ID: <CACvgo516ewfwGCpV=noX+re1x8t3Sp1t39Sha+A2-tQ5YsoihA@mail.gmail.com>
Date:	Mon, 28 Mar 2016 23:07:59 +0100
From:	Emil Velikov <emil.l.velikov@...il.com>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	Yakir Yang <ykk@...k-chips.com>, David Airlie <airlied@...ux.ie>,
	Mark Yao <mark.yao@...k-chips.com>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	Kumar Gala <galak@...eaurora.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Russell King <linux@....linux.org.uk>,
	devicetree <devicetree@...r.kernel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	ML dri-devel <dri-devel@...ts.freedesktop.org>,
	linux-rockchip <linux-rockchip@...ts.infradead.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH v1 0/4] Add Rockchip RGA support

On 28 March 2016 at 22:46, Heiko Stübner <heiko@...ech.de> wrote:
> Am Montag, 28. März 2016, 22:35:36 schrieb Emil Velikov:
>> On 28 March 2016 at 19:44, Heiko Stübner <heiko@...ech.de> wrote:
>> > Am Montag, 28. März 2016, 13:21:02 schrieb Emil Velikov:
>> >> On 22 March 2016 at 00:42, Heiko Stuebner <heiko@...ech.de> wrote:
>> >> > Hi Yakir,
>> >> >
>> >> > Am Montag, 21. März 2016, 20:17:46 schrieb Yakir Yang:
>> >> >> On 03/21/2016 07:29 PM, Heiko Stübner wrote:
>> >> >> > Am Montag, 21. März 2016, 17:28:38 schrieb Yakir Yang:
>> >> >> >> This patch set would add the RGA direct rendering based 2d graphics
>> >> >> >> acceleration module.
>> >> >> >
>> >> >> > very cool to see that.
>> >> >>
>> >> >> ;)
>> >> >>
>> >> >> >> This patch set is based on git repository below:
>> >> >> >> git://people.freedesktop.org/~airlied/linux drm-next
>> >> >> >> commit id: 568d7c764ae01f3706085ac8f0d8a8ac7e826bd7
>> >> >> >>
>> >> >> >> And the RGA driver is based on Exynos G2D driver, it only manages
>> >> >> >> the
>> >> >> >> command lists received from user, so user should make the command
>> >> >> >> list
>> >> >> >> to data and registers needed by operation to use.
>> >> >> >>
>> >> >> >> I have prepared an userspace demo application for testing:
>> >> >> >>    https://github.com/yakir-Yang/libdrm-rockchip
>> >> >> >>
>> >> >> >> That is a rockchip libdrm library, and I have write a simple test
>> >> >> >> case
>> >> >> >> "rockchip_rga_test" that would test the below RGA features:
>> >> >> >> - solid
>> >> >> >> - copy
>> >> >> >> - rotation
>> >> >> >> - flip
>> >> >> >> - window clip
>> >> >> >> - dithering
>> >> >> >
>> >> >> > Did you submit your libdrm changes as well?
>> >> >> >
>> >> >> > Userspace-interfaces need to be stable so the other side must also
>> >> >> > get
>> >> >> > accepted - even before the kernel change if I remember correctly.
>> >> >>
>> >> >> Got it, and I just saw exynos_fimg2d already landed at mainline
>> >> >> libdrm.
>> >> >> But I don't find the way to submit patches to libdrm, would you like
>> >> >> share some helps here ;)
>> >> >
>> >> > Looking at the libdrm sources on cgit.freedesktop.org, I did not find
>> >> > any
>> >> > specific manual on submitting patches.
>> >> >
>> >> > But looking at the dri-list archive, dri-devel@...ts.freedesktop.org is
>> >> > the
>> >> > right list and looking at the libdrm history it looks like Emil Velikov
>> >> > <emil.l.velikov@...il.com> seems to be doing maintenance-stuff in
>> >> > libdrm.
>> >> > And as a 3rd recipient, please also include the linux-rockchip list.
>> >> >
>> >> > @Emil, please shout if I read that wrong :-)
>> >>
>> >> You got it spot on Heiko. There are a few notes though...
>> >>
>> >> As one reuses the existing hardware/IP block, it would be better to
>> >> avoid copy/pasting code around.
>> >>
>> >> Namely:
>> >>  - (if possible) factor out the exynos g2d kernel functionality to a
>> >>
>> >> separate kernel module and wire up the rockhip (via dt ?) to use it
>> >>
>> >>  - factor out the g2d specifics out of exynos_drm.h (into
>> >>
>> >> exynos_g2d_drm.h perhaps ?) and make sure exynos_drm.h includes the
>> >> new header
>> >
>> > I think the IP blocks themself are quite different between Rockchip's RGA
>> > and Samsung's g2d and I guess the similarities are more along the lines
>> > on how that gets integrated into the respective drm driver and userspace.
>> In this case, the exynos_g2d_drm.h seems like a good idea. As I'm
>> obviously biased, it's better to check how others feel on the topic.
>>
>> >>  - if neither of these are possible, then please ensure that the new
>> >>
>> >> header uses correct types (see the docs [1]), use MIT/X11 license (if
>> >> possible) and link where upstream userspace is happy with the
>> >> interface (ideally more than a simple test app like libdrm)
>> >> These might sound like an overkill, although getting UAPI right and
>> >> maintaining it forever forces us to do so.
>> >
>> > As for a real-world usecase, maybe the armsoc xserver might be somewhat
>> > easy to use. While the core changes I did are in the core project
>> > already, I'm still keeping the actual Rockchip support separate [0] due
>> > to the not-yet- resolved create_gem ioctl.
>> >
>> > Anyway, the armsoc xserver has some exa implementation hooks were I guess
>> > it might be relatively easy to hook up soc-specific things.
>>
>> Ouch the armsoc ddx... Last time I've checked it felt like a place
>> where everyone is doing his own thing, with no actual reviews and/or
>> maintainer.
>
> The development rate is pretty low and maintainership is unclear but the per-
> soc voodoo is quite limited to the GEM-creation and everything else seems
> somewhat nice when compared for example to the older versions of the ddx.
>
>
>> Iirc most/all of it's functionality was achievable with
>> modesetting ddx (with or without glamor) ? I take it that things have
>> changed and/or I misunderstood something ?
>
> I don't really understand that whole stack or how xservers work on a whole ;-)
> I was merely able to make the _binary_ mali-driver work with this one and
> remembered that there were hooks for future per-soc exa functions.
>
> I guess for that glamor thing you'd need an actual gpu driver and not that
> libGL-override voodoo those crazy binary drivers do.
>
> At least the modesetting ddx didn't like mali-binary-driver.
>
A quick rundown of the whole thing (simplified and maybe slightly off)
- the modesetting DDX (merged in xserver for a few releases now),
relies on GBM for buffer management and GL{,ES} for acceleration. On
the KMS side it's as generic as any other driver should be.

I'm not sure how well modesetting works without gbm, but it should be
able to build at least. About getting it (or others) to work with
binary blobs... I guess you know what my and others' view is. Place
the fact that one tries to upstream a kernel interface which,
indirectly, interacts with such a module makes things even more ...
lovely.

Sorry to be the bearer of bad news. If you have other ideas or others
feels like I'm overly dramatic let me know, please.

-Emil

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