Re: [PATCH v2 3/5] media: mediatek: vcodec: Read HW active status from clock

[AngeloGioacchino Del Regno]

Il 09/06/23 01:56, Stephen Boyd ha scritto:
> Quoting AngeloGioacchino Del Regno (2023-06-08 02:01:58)
> > Il 08/06/23 10:12, Chen-Yu Tsai ha scritto:
> > > On Thu, Jun 8, 2023 at 4:57 AM Nícolas F. R. A. Prado
> > > <nfraprado@xxxxxxxxxxxxx> wrote:
> > > > diff --git a/drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec_drv.c b/drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec_drv.c
> > > > index 9c652beb3f19..8038472fb67b 100644
> > > > --- a/drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec_drv.c
> > > > +++ b/drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec_drv.c
> > > > @@ -16,6 +16,7 @@
> > > >    #include <media/v4l2-mem2mem.h>
> > > >    #include <media/videobuf2-dma-contig.h>
> > > >    #include <media/v4l2-device.h>
> > > > +#include <linux/clk-provider.h>
> > >
> > >                      ^^^^^^^^^^^^^^
> > >
> > > This seems like a violation of the API separation.
>
> Yes.
>
> > > >    #include "mtk_vcodec_drv.h"
> > > >    #include "mtk_vcodec_dec.h"
> > > > @@ -38,22 +39,29 @@ static int mtk_vcodec_get_hw_count(struct mtk_vcodec_dev *dev)
> > > >           }
> > > >    }
> > > >
> > > > +static bool mtk_vcodec_is_hw_active(struct mtk_vcodec_dev *dev)
> > > > +{
> > > > +       u32 cg_status = 0;
> > > > +
> > > > +       if (!dev->reg_base[VDEC_SYS])
> > > > +               return __clk_is_enabled(dev->pm.vdec_active_clk);
> > >
> > > AFAIK this is still around for clk drivers that haven't moved to clk_hw.
> > > It shouldn't be used by clock consumers. Would it be better to just pass
> > > a syscon?
> >
> > This is a legit usage of __clk_is_enabled().... because that's what we're really
> > doing here, we're checking if a clock got enabled by the underlying MCU (as that
> > clock goes up after the VDEC boots).
> >
> > If this is *not* acceptable as it is, we will have to add a clock API call to
> > check if a clock is enabled... but it didn't seem worth doing since we don't
> > expect anyone else to have any legit usage of that, or at least, we don't know
> > about anyone else needing that...
>
> The design of the clk.h API has been that no clk consumer should need to
> find out if a clk is enabled. Instead, the clk consumer should enable
> the clk if they want it enabled. Is there no other way to know that the
> vcodec hardware is active?

The firmware gives an indication of "boot done", but that's for the "core" part
of the vcodec... then it manages this clock internally to enable/disable the
"compute" IP of the decoder.

As far as I know (and I've been researching about this) the firmware will not
give any "decoder powered, clocked - ready to get data" indication, and the
only way that we have to judge whether it is in this specific state or not is
to check if the "VDEC_ACTIVE" clock got enabled by the firmware.

That's *synthetically* the whole story...

> > As for the syscon, that's something that we've been discussing as well... the
> > thing is: we're really *really* checking if a clock is enabled, so we should
> > be using clock related calls... reading from a syscon means that we'd have to
> > perform a register read (of.. again.. a clock) outside of the clock framework
> > which, in my opinion, wouldn't be clean; I'd expect that to become a bit messy
> > in the future too, should more MediaTek SoCs (I think MT8192/95 are already in
> > the list, Nicolas please correct me if I'm wrong here) need the same thing, as
> > we'd be adding more definitions around.