Re: [BUG] simplefb not showing any output

[Stephen Warren <swarren@wwwdotorg.org>]

On 09/07/2013 06:25 AM, David Herrmann wrote:
> On Sat, Sep 7, 2013 at 1:47 PM, Tom Gundersen <teg@jklm.no> wrote:
...
>> A related question: is it expected that simplefb should be
>> significantly slower than efifb, or is that something worth looking
>> into? My boot with simplefb is roughly five seconds slower than with
>> efifb. Coincidentally, I notice the same (or similar slowdown) with
>> inteldrmfb when I see the oops (but not otherwise).
> 
> That is probably related to the missing write-combine tag in ioremap.
> Stephen, any objections to this attached patch?
> Tom, if this solves the speed-issues, I will send it out once I get home.
> 
> Thanks
> David
> 
> (Patch also attached in case of new-lines issues)
> 
> From dbfb8e12166d494cd60823cbe84134d5d1a73ec8 Mon Sep 17 00:00:00 2001
> From: David Herrmann <dh.herrmann@gmail.com>
> Date: Sat, 7 Sep 2013 14:22:01 +0200
> Subject: [PATCH] devm/simplefb: introduce and use devm_ioremap_wc()
> 
> We want to use devm_ioremap_nocache() or even devm_ioremap_wc() to speed
> up fbdev writes _a lot_. As devm_ioremap_wc() doesn't exist, yet,
> introduce it along the way. Note that ioremap_wc() is aliases to
> ioremap_nocache() in asm-generic/{io,iomem}.h so we can safely expect all
> architectures to either provide it or use the same alias.

I'm fine with this so long as wc mappings are always possible, or
automatically fall back to uc if not. This certainly works on Tegra, and
I'll try to remember to test it on Raspberry Pi tonight.