[Letux-kernel] tiled fbdev

Matthijs van Duin matthijsvanduin at gmail.com
Mon Sep 5 23:13:47 CEST 2016

Limited time right now, but I'll at least reply to a few things:

On 5 September 2016 at 18:43, H. Nikolaus Schaller <hns at goldelico.com> wrote:
> Well, kernel parameters are IMHO very old style. I think the better way

As I've pointed out more than once these are just dirty hacks to get
things into a state where testing could be done with TILER-based
rotation. I even marked the hacky commits with XXX in the subject line
to discourage merging.

The kernel param was simply the closest thing within reach of
copy-paste to at least let me avoid the need to recompile.

Of course it /should/ be handled by the panel advertising its native
orientation via DT, although I'm not quite decided yet on which code
can and should carry the responsibility of taking it into account.
Right now I hacked it into drm_kms_helper but that's just for legacy
fbdev, which we may want to ditch altogether sooner or later. In fact
sorting out how we want to organise userspace w.r.t graphics is much
higher on my priority list right now then cleaning up my patches.

In principle the kernel could completely hide the true orientation of
the panel from userspace, but it would be non-trivial, break
libdrm-omap (don't really care about that though), and unnecessarily
decrease 3D performance (compared to allocating non-tiled buffers and
reporting the screen rotation from the WSEGL backend in userspace).

>> Rotation values are same as for the DRM "rotation" property:
> that looks like a strange encoding for a rotation angle

Yeah it's a bit dirty but it lets DRM use a bitmask property type to
indicate which orientations are actually supported.

>> arch/arm/mach-omap2/omap-smp.c: In function 'omap4_smp_prepare_cpus':
>> arch/arm/mach-omap2/omap-smp.c:301:3: error: too few arguments to function 'omap5_erratum_workaround_801819'
>>    omap5_erratum_workaround_801819();

I've only touched that file in patch/fast-nc-read (commit
912c3f254c9e), which applies cleanly against mainline rc5 for me.

Note that this patch is a performance enhancement separate from TILER work.

>> I've also polished the letux_defconfig a bit to remove stuff
>> irrelevant to omap5 and some other changes here and there.
> Well, please rename the config to a private one (pyraonly_defconfig?).

Will do.

> The core principle of letux_defconfig is to support a multitude of devices

Keep in mind that 4GB of ram in the Pyra will mean an LPAE kernel is
required, which will not boot at all on cortex-a8/a9 devices.


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