[U-Boot] [PATCH] sunxi: display: Align end of memory to work around a linux-4.0 bug

[Mark Rutland]

On Mon, May 04, 2015 at 10:36:43AM +0100, Ian Campbell wrote:
> On Mon, 2015-05-04 at 10:51 +0200, Hans de Goede wrote:
> > Hi,
> > 
> > On 02-05-15 15:21, Ian Campbell wrote:
> > > On Fri, 2015-04-24 at 20:39 +0200, Hans de Goede wrote:
> > >> Linux-4.0 as shipped has a bug causing it to not boot if the end of memory
> > >> is not aligned to a multiple of 2 MiB. For details see the linux-arm
> > >> mailing list post titled:
> > >> "Memory size unaligned to section boundary"
> > >> http://www.spinics.net/lists/arm-kernel/msg413811.html
> > >>
> > >> This is something which specifically hits the sunxi display driver because
> > >> we carve out the exact needed framebuffer size at the top of mem, this
> > >> commit works around this issue by aligning the carve out.
> > >
> > > I'm afraid I don't like this, we shouldn't be working around Linux bugs
> > > in the firmware, especially when both are Free software. Lets just fix
> > > Linux and get the fix into the appropriate stable trees and in the
> > > meantime tell people to avoid this buggy kernel.
> > >
> > > The problem with this sort of thing is that it is very hard to get rid
> > > of these workarounds, even once the underlying issue is fixed and we no
> > > longer care about the versions with the bug OS authors (including
> > > non-Linux OSes) can inadvertently come to rely on the quirky behaviour,
> > > (i.e. the work around masks other bugs). Hence we end up in a
> > > quirks-race as everyone works around the other parties last workaround.
> > >
> > > If there is to be a workaround instead of a fix then it should be for
> > > Linux to align memory to 2MB boundaries if that is what it requires.
> > 
> > I can understand where you're coming from, the problem is that despite
> > various mails to the arm kernel mailing list no one from the upstream
> > kernel seems to be looking into this,
> 
> Mark, do you think you could find some cycles (not necessarily your own)
> to look at this, or perhaps you know the appropriate maintainers to
> ping?

I'll have another look and see if I can come up with a kernel patch.
Perhaps proposing something (even if slightly wrong) will provoke people
to respond.

> I'd really like to avoid having to hack around kernel bugs in the
> firmware.

Likewise.

Mark.