[linux-sunxi] Re: [PATCH 4/4] simplefb: add clock handling code

[Thierry Reding]

On Tue, Aug 26, 2014 at 02:33:57PM +0200, Luc Verhaegen wrote:
> On Tue, Aug 26, 2014 at 02:21:16PM +0200, Thierry Reding wrote:
> > On Tue, Aug 26, 2014 at 02:02:58PM +0200, Luc Verhaegen wrote:
> > > On Tue, Aug 26, 2014 at 09:52:49AM +0200, Thierry Reding wrote:
> > > > On Mon, Aug 25, 2014 at 05:09:00PM +0200, Luc Verhaegen wrote:
> > > > > On Mon, Aug 25, 2014 at 05:05:04PM +0200, Thierry Reding wrote:
> > > > > > 
> > > > > > No. simplefb just wants to write to some memory that hardware has been
> > > > > > set up to scan out. The platform requires that the clocks be on.
> > > > > 
> > > > > Simplefb also requires that the memory is there and is persistent. Fine 
> > > > > for discrete graphics cards, fine for rpi where most things are hidden 
> > > > > from the ARM core anyway, not so fine for anybody else.
> > > > 
> > > > I don't understand. This patch series isn't changing anything about the
> > > > memory aspects of the driver yet it's working for you on sunxi, isn't
> > > > it? So it can't be all that broken.
> > > > 
> > > > Thierry
> > > 
> > > Oh, i had to go wrestle with UBoot options and reserve 8MB off the top, 
> > > which the kernel never gets told about. A nice throwback to x86 IGP 
> > > bioses, a past i had thought i had left behind forgood.
> > 
> > Can you not use the reserved memory code (drivers/of/of_reserved_mem.c
> > in the kernel)? I think that's the generally accepted way to do this
> > with DT.
> > 
> > Thierry
> 
> It was mentioned to me, and I probably could do that, but this seemed 
> even more DT wrangling from within u-boot, and it didn't seem finished 
> yet. Plus, all of this already was way more wrangling than i bargained 
> for, especially with the promise of "simple"-fb. Then there is the 
> really awkward way in which one gets to define clocks outside of a 
> dts/compiler (you've seen the code, right?), i really did not feel like 
> repeating something like that.

It could most probably be turned into fairly generic and reusable code
so that others can use it. And it would give you a way of recovering
those 8 MiB of memory that you'd otherwise loose.

Thierry
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