Re: [PATCH 0/2] Follow-up patches for Cedrus v9

From: Chen-Yu Tsai
Date: Sat Sep 08 2018 - 06:24:19 EST

On Sat, Sep 8, 2018 at 6:06 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
> On 09/07/2018 06:33 PM, Paul Kocialkowski wrote:
> > This brings the requested modifications on top of version 9 of the
> > Cedrus VPU driver, that implements stateless video decoding using the
> > Request API.
> >
> > Paul Kocialkowski (2):
> > media: cedrus: Fix error reporting in request validation
> > media: cedrus: Add TODO file with tasks to complete before unstaging
> >
> > drivers/staging/media/sunxi/cedrus/TODO | 7 +++++++
> > drivers/staging/media/sunxi/cedrus/cedrus.c | 15 ++++++++++++---
> > 2 files changed, 19 insertions(+), 3 deletions(-)
> > create mode 100644 drivers/staging/media/sunxi/cedrus/TODO
> >
> So close...
> When compiling under e.g. intel I get errors since it doesn't know about
> the sunxi_sram_claim/release function and the PHYS_PFN_OFFSET define.
> Is it possible to add stub functions to linux/soc/sunxi/sunxi_sram.h
> if CONFIG_SUNXI_SRAM is not defined? That would be the best fix for that.
> The use of PHYS_PFN_OFFSET is weird: are you sure this is the right
> way? I see that drivers/of/device.c also sets dev->dma_pfn_offset, which
> makes me wonder if this information shouldn't come from the device tree.
> You are the only driver that uses this define directly, which makes me
> suspicious.

On Allwinner platforms, some devices do DMA directly on the memory BUS
with the DRAM controller. In such cases, the DRAM has no offset. In all
other cases where the DMA goes through the common system bus and the DRAM
offset is either 0x40000000 or 0x20000000, depending on the SoC. Since the
former case is not described in the device tree (this is being worked on
by Maxime BTW), the dma_pfn_offset is not the value it should be. AFAIK
only the display and media subsystems (VPU, camera, TS) are wired this

In drivers/gpu/drm/sun4i/sun4i_backend.c (the display driver) we use
PHYS_OFFSET, which is pretty much the same thing.