linux-kernel - Re: [PATCH 4/10] atyfb: set FBINFO_READS

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Message-ID: <CA+55aFxrZE6oxu5CxFo3mRwGdVcq3jvnn_ChoSJDFgQz45Lq_A@mail.gmail.com>
Date:	Thu, 23 Jan 2014 11:45:26 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/10] atyfb: set FBINFO_READS_FAST

On Thu, Jan 23, 2014 at 11:31 AM, Mikulas Patocka <mpatocka@...hat.com> wrote:
>
> Both mach64 and matrox have a hardware bitter that is faster than
> rewriting the console - that's why FBINFO_READS_FAST improves performance
> for them.

My point is that I'd expect *anything* that has a hardware blitter to
be faster than rewriting the screen.

FBINFO_READS_FAST is documented to be about "soft-copy" being faster
than re-rendering. Which I take to be about actually doing copying in
*software*.

In particular, updatescrollmode() seems to do this right. It sets
p->scrollmode based on whether there's an accelerated copyarea. But
then SCROLL_PAN/WRAP_MOVE ends up re-testing FBINFO_READS_FAST,
ignoring any hw-accelerated copy-area, and I don't quite see why..

                Linus
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