linux-kernel - Re: [RFC PATCH v2 03/13] bootsplash: Flush framebuffer after drawing

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Message-ID: <20171220094527.GK26573@phenom.ffwll.local>
Date:   Wed, 20 Dec 2017 10:45:28 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Max Staudt <mstaudt@...e.de>
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        michal@...kovi.net, sndirsch@...e.com,
        Oliver Neukum <oneukum@...e.com>,
        Takashi Iwai <tiwai@...e.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bero Rosenkränzer 
        <bernhard.rosenkranzer@...aro.org>, philm@...jaro.org
Subject: Re: [RFC PATCH v2 03/13] bootsplash: Flush framebuffer after drawing

On Tue, Dec 19, 2017 at 05:23:52PM +0100, Max Staudt wrote:
> On 12/19/2017 05:02 PM, Daniel Vetter wrote:
> > On Tue, Dec 19, 2017 at 4:41 PM, Max Staudt <mstaudt@...e.de> wrote:
> >> On 12/19/2017 02:57 PM, Daniel Vetter wrote:
> >>> The problem is that defio is totally not how a real driver works.
> >>
> >> But they do exist and I can't ignore them.
> >>
> >> I'm afraid I don't understand - why are those, such as xenfb, not real drivers?
> > 
> > I mean kms drivers. The problem is that the magic mapping that fbdev
> > expects is real pain. Everyone else, including kms, expects an
> > explicit flush operation. So instead of hacking around even more with
> > the defio corner cases that don't work, I'm suggesting we just add
> > that flush operation. At least internally.
> > 
> > Fixing kms drivers to implement a better defio is probably not a
> > reasonable investement of time.
> 
> Ah yes, I understand now, you mean that KMS drivers have explicit flush,
> and defio is a hack to retrofit such drivers to an API that never
> supported a flush operation (the fbdev API), but always used to expose
> the video memory directly. Right?
> 
> If yes, then I agree. Fixing the defio in the KMS drivers wouldn't even
> solve my problem - I'd still need to implement flush. So might as well
> care about the flush straight away, yep!

Yup.

I'll leave the more fundamental discussion to the other thread on the
cover letter.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch