linux-kernel - Re: [PATCH v2] media: mtk-vcodec: fix builds when remoteproc is disabled

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Date:   Mon, 12 Oct 2020 13:58:51 +0900
From:   Alexandre Courbot <acourbot@...omium.org>
To:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc:     Hans Verkuil <hverkuil-cisco@...all.nl>,
        Tiffany Lin <tiffany.lin@...iatek.com>,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support
        <linux-mediatek@...ts.infradead.org>, Randy Dunlap" 
        <rdunlap@...radead.org>
Subject: Re: [PATCH v2] media: mtk-vcodec: fix builds when remoteproc is disabled

Hi Mauro,

On Fri, Oct 9, 2020 at 3:34 PM Mauro Carvalho Chehab
<mchehab+huawei@...nel.org> wrote:
>
> Em Fri, 9 Oct 2020 13:30:06 +0900
> Alexandre Courbot <acourbot@...omium.org> escreveu:
>
> > On Fri, Oct 9, 2020 at 1:13 AM Hans Verkuil <hverkuil-cisco@...all.nl> wrote:
>
> > > >>> If VIDEO_MEDIATEK_VPU=y and MTK_SCP=m, then VIDEO_MEDIATEK_VCODEC can be configured
> > > >>> to y, and then it won't be able to find the scp_ functions.
> > > >>>
> > > >>> To be honest, I'm not sure how to solve this.
> > > >>
> > > >> Found it. Add this:
> > > >>
> > > >>         depends on MTK_SCP || !MTK_SCP
> > > >>         depends on VIDEO_MEDIATEK_VPU || !VIDEO_MEDIATEK_VPU
> > > >>
> > > >> Ugly as hell, but it appears to be the correct incantation for this.
>
> While the above does the job, I'm wondering if the better wouldn't
> be to have this spit into 3 config dependencies. E. g. something like:
>
> config VIDEO_MEDIATEK_CODEC
>         depends on VIDEO_MEDIATEK_VPU_SCP || VIDEO_MEDIATEK_VPU
>
> config VIDEO_MEDIATEK_VPU
>         depends on VIDEO_DEV && VIDEO_V4L2
>         depends on ARCH_MEDIATEK || COMPILE_TEST
>         tristate "support for Mediatek Video Processor Unit without SCP"
>         help
>             ...
>
> config VIDEO_MEDIATEK_VPU_SCP
>         depends on VIDEO_DEV && VIDEO_V4L2
>         depends on ARCH_MEDIATEK || COMPILE_TEST
>         tristate "support for Mediatek Video Processor Unit with SCP"
>         help
>             ...

Doing so would introduce two extra choices to enable the driver, so
I'm a bit concerned this may be a bit confusing?

Also I have experimented with this, and it appears that
VIDEO_MEDIATEK_CODEC won't be automatically enabled if one of the new
options is selected. So this means that after setting e.g.
VIDEO_MEDIATEK_VPU_SCP, one still needs to manually enable
VIDEO_MEDIATEK_CODEC otherwise the driver won't be compiled at all.

>
> And split the board-specific data for each variant on separate files,
> doing something like this at the Makefile:
>
>         obj-$(CONFIG_VIDEO_MEDIATEK_VCODEC) += mtk-vcodec-dec.o \
>                                        mtk-vcodec-enc.o \
>                                        mtk-vcodec-common.o
>
>         ifneq ($(VIDEO_MEDIATEK_VPU_SCP),)
>         obj-$(CONFIG_VIDEO_MEDIATEK_VCODEC) += mtk-vcodec-fw-scp.o
>         endif
>
>         ifneq ($(VIDEO_MEDIATEK_VPU),)
>         obj-$(CONFIG_VIDEO_MEDIATEK_VCODEC) += mtk-vcodec-fw-vpu.o
>         endif
>
> This will avoid the ugly ifdefs in the middle of mtk_vcodec_fw.c,
> and the ugly "depends on FOO || !FOO" usage.
>
> It should also be simpler to add future variants of it in the
> future, if needed.

Indeed, the split makes sense regardless of the selection mechanism
adopted. I will try to do it in the next revision.