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SubjectRe: [PATCH v10 0/8] Add MT8173 Video Encoder Driver and VPU Driver
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Hi Hans,

On Wed, 2016-05-04 at 10:25 +0200, Hans Verkuil wrote:
>
> On 05/04/2016 10:19 AM, tiffany lin wrote:
> > Hi Hans,
> >
> > On Wed, 2016-05-04 at 09:32 +0200, Hans Verkuil wrote:
> >> Hi Tiffany,
> >>
> >> On 05/03/2016 12:11 PM, Tiffany Lin wrote:
> >>> ==============
> >>> Introduction
> >>> ==============
> >>>
> >>> The purpose of this series is to add the driver for video codec hw embedded in the Mediatek's MT8173 SoCs.
> >>> Mediatek Video Codec is able to handle video encoding of in a range of formats.
> >>>
> >>> This patch series also include VPU driver. Mediatek Video Codec driver rely on VPU driver to load,
> >>> communicate with VPU.
> >>>
> >>> Internally the driver uses videobuf2 framework and MTK IOMMU and MTK SMI both have been merged in v4.6-rc1.
> >>> This patch series need [PATCH v15 8/8] memory: mtk-smi: export mtk_smi_larb_get/put[1] to build as module
> >>>
> >>> [1]http://lists.infradead.org/pipermail/linux-mediatek/2016-April/005173.html
> >>>
> >>> ==================
> >>> Device interface
> >>> ==================
> >>>
> >>> In principle the driver bases on v4l2 memory-to-memory framework:
> >>> it provides a single video node and each opened file handle gets its own private context with separate
> >>> buffer queues. Each context consist of 2 buffer queues: OUTPUT (for source buffers, i.e. raw video
> >>> frames) and CAPTURE (for destination buffers, i.e. encoded video frames).
> >>>
> >>> ==============================
> >>> VPU (Video Processor Unit)
> >>> ==============================
> >>> The VPU driver for hw video codec embedded in Mediatek's MT8173 SOCs.
> >>> It is able to handle video decoding/encoding in a range of formats.
> >>> The driver provides with VPU firmware download, memory management and the communication interface between CPU and VPU.
> >>> For VPU initialization, it will create virtual memory for CPU access and physical address for VPU hw device access.
> >>> When a decode/encode instance opens a device node, vpu driver will download vpu firmware to the device.
> >>> A decode/encode instant will decode/encode a frame using VPU interface to interrupt vpu to handle decoding/encoding jobs.
> >>>
> >>> Please have a look at the code and comments will be very much appreciated.
> >>>
> >>> Change in v10:
> >>> 1. Fix smatch/sparse error message
> >>> 2. Add depends on ARM || ARM64 and MTK_IOMMU in Kconfig
> >>
> >> I don't like the ARM or ARM64 dependency since that makes COMPILE_TEST harder.
> >>
> >> I removed it here and for the VPU and everything still compiles fine with
> >> sparse and smatch. So I'll drop those dependencies.
> >>
> >> Why is the MTK_IOMMU dependency needed? Just curious.
> >>
> > This is because we need MTK_IOMMU module to get dma continuous memory
> > for HW.
> >
> >> Note that sparse still complains about this:
> >>
> >> media-git/drivers/media/platform/mtk-vcodec/venc/venc_vp8_if.c:261:24: warning: incorrect type in assignment (different base types)
> >>
> >> I think this code should be rewritten. Something like this would work
> >> (if I understand the code correctly):
> >>
> >> u32 tag = (bs_hdr_len << 5) | 0x10 | not_key;
> >>
> >> ac_tag[0] = tag & 0xff;
> >> ac_tag[1] = (tag >> 8) & 0xff;
> >> ac_tag[2] = (tag >> 16) & 0xff;
> >>
> >> It's perhaps a bit more verbose, but a lot easier to understand.
> >>
> >
> >> I'm accepting this driver but I'll remove the ARM || ARM64 dependency. Can
> >> you post a follow-up patch for this sparse warning?
> >>
> >
> > Got it. We will provide a patch to fix this.
> > I was curious why my sparse do not show this warning.
> > Is there any parameter I need to set except C=1?
>
> I'm running it with these parameters: C=2 CF="-D__CHECK_ENDIAN__"
>
> I suspect it is the CHECK_ENDIAN flag that does it.
>
Got it, thanks for the information.

best regards,
Tiffany
> Regards,
>
> Hans


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