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

[Mark Rutland]

On Tue, May 05, 2015 at 10:39:14AM +0100, Mark Rutland wrote:
> 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.

For the benefit of anyone not on the Linux ARM kernel list there's now a
patch addressing the issue [1].

Mark.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-May/342210.html