[U-Boot] [PATCH] Revert "sunxi: dram: Use divisor P=1 for PLL5"

[Tom Rini]

On Thu, Oct 16, 2014 at 10:48:34AM +0200, Hans de Goede wrote:
> Hi,
> 
> On 10/15/2014 12:34 PM, Siarhei Siamashka wrote:
> > On Wed, 15 Oct 2014 12:12:11 +0200
> > Hans de Goede <hdegoede at redhat.com> wrote:
> > 
> >> This change breaks various hardcoded assumptions in the linux-sunxi-3.4
> >> kernels, causing a divide by 0 error in the linux-sunxi-3.4 nand driver,
> >> rendering 3.4 kernels unbootable. Besides this problem, it also breaks LCD
> >> output (on devices without nand).
> >>
> >> Fixes for these issues are being added to the linux-sunxi-3.4 kernel, but for
> >> now it seems better to revert this.
> >>
> >> This reverts commit 013f2d746955147439215a4939655c9ed6bdd866.
> > 
> > As mentioned in the commit message
> >     https://www.mail-archive.com/linux-sunxi@googlegroups.com/msg07884.html
> > the hardcoded assumptions in the sunxi-3.4 kernel are still bad
> > with or without this revert if somebody tries to use higher DRAM
> > clock speeds.
> > 
> > The patch in question just smokes out bugs, which are otherwise still
> > there.
> > 
> > Going forward, the mainline kernel needs the G2D driver and it needs
> > to run at a decent clock speed to be provide reasonable performance.
> > Low PLL5P clock speed is limiting our options.
> > 
> > This revert does not do anyone any favour and only postpones the
> > resolution of the problem.
> 
> I agree that we need to fix the linux-sunxi-3.4 kernels to work properly with
> different pll5 settings, which is why I've actually send a fix for some pll5
> issues to the linux-sunxi list and acked your patches which fix other bits.
> 
> I can understand you want to have optimal settings for the G2D stuff, and I'm
> not against that. But getting the G2D stuff upstream is something which
> is still far in the future. I really want people to be able to start using
> upstream u-boot, starting today. And it will take some time for the sunxi-3.4
> fixes to trickle down to users.

We should be doing things right, in mainline.  To bring up a different
example, on TI OMAP4 parts at least for a long time in order to use
mainline U-Boot on older kernels you had to manually add
CONFIG_SOMETHING_OR_ANOTHER to enable additional clocks/mux that the old
kernels had incorrectly relied on U-Boot to set.  If we must do strange
things to support old and incorrect but in the wild kernels we need to
(a) make it opt-in (easier now with Kconfig!) and (b) schedule a removal
of the hack all the same.

-- 
Tom
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