[PATCH 5/6] drm/mediatek: Convert to use CMA helpers

[CK Hu]

Hi, Rob:

On Wed, 2019-10-23 at 12:42 -0500, Rob Herring wrote:
> On Tue, Oct 22, 2019 at 12:07 PM Matthias Brugger
> <matthias.bgg at gmail.com> wrote:
> >
> > Hi Rob,
> >
> > On 21/10/2019 23:45, Rob Herring wrote:
> > > The only reason the Mediatek driver doesn't use the CMA helpers is it
> > > sets DMA_ATTR_NO_KERNEL_MAPPING and does a vmap() on demand. Using
> > > vmap() is not even guaranteed to work as DMA buffers may not have a
> > > struct page. Now that the CMA helpers support setting
> > > DMA_ATTR_NO_KERNEL_MAPPING as needed or not, convert Mediatek driver to
> > > use CMA helpers.
> > >
> > > Cc: CK Hu <ck.hu at mediatek.com>
> > > Cc: Philipp Zabel <p.zabel at pengutronix.de>
> > > Cc: David Airlie <airlied at linux.ie>
> > > Cc: Daniel Vetter <daniel at ffwll.ch>
> > > Cc: Matthias Brugger <matthias.bgg at gmail.com>
> > > Cc: linux-arm-kernel at lists.infradead.org
> > > Cc: linux-mediatek at lists.infradead.org
> > > Signed-off-by: Rob Herring <robh at kernel.org>
> > > ---
> >
> > I tested this on my Chromebook with some patches on top of v5.4-rc1 [1], which
> > work. If I add your patches on top of that, the system does not boot up.
> > Unfortunately I don't have a serial console, so I wasn't able to see if there is
> > any error message.
> 
> Thanks for testing. I'm based on drm-misc-next, but don't see anything
> obvious there that would matter. There are some mmap changes, but I
> think they shouldn't matter.
> 
> Did you have fbcon enabled? That may give more clues about where the problem is.

There are priv->dma_dev for dma device, but it is not drm device. In
mt8173.dtsi [1], there are mmsys device and ovl device, mmsys device is
drm device and ovl device is mmsys's sub device which provide dma
function, so ovl is the priv->dma_dev. I think your patch directly use
drm device for dma operation and this would cause dma function fail.
Please use priv->dma_dev for dma operation.

Regards,
CK

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/mediatek/mt8173.dtsi?h=v5.4-rc4
> 
> Rob