linux-kernel - Re: [PATCH 2/2] clk: meson: meson8b: add the video decoder clock trees

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Date:   Thu, 21 Mar 2019 12:42:45 +0100
From:   Maxime Jourdan <mjourdan@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        linux-amlogic@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] clk: meson: meson8b: add the video decoder clock trees

On Wed, Mar 20, 2019 at 9:53 PM Martin Blumenstingl
<martin.blumenstingl@...glemail.com> wrote:
>
> Hi Maxime,
>
> On Wed, Mar 20, 2019 at 12:16 PM Maxime Jourdan <mjourdan@...libre.com> wrote:
> >
> > Hi Martin, thanks for looking into the video decoder for meson8!
> you're welcome - this is only possible because of your work on the
> video decoder driver!
>
> > On Tue, Mar 19, 2019 at 11:00 PM Martin Blumenstingl
> > <martin.blumenstingl@...glemail.com> wrote:
> > >
> > > This adds the four video decoder clock trees.
> > >
> > > VDEC_1 is split into two paths on Meson8b and Meson8m2:
> > > - input mux called "vdec_1_sel"
> > > - two dividers ("vdec_1_1_div" and "vdec_1_2_div") and gates ("vdec_1_1"
> > >   and "vdec_1_2")
> > > - and an output mux (probably glitch-free) called "vdec_1"
> >
> > Yes, all vdec clocks have a glitch-free mux to be able to safely
> > adjust the frequency on the fly, although in practice it's barely
> > used.
> >
> > > On Meson8 the VDEC_1 tree is simpler because there's only one path:
> > > - input mux called "vdec_1_sel"
> > > - divider ("vdec_1_1_div") and gate ("vdec_1_1")
> > > - (the gate is used as output directly, there's no mux)
> > >
> > > The VDEC_HCODEC and VDEC_2 clocks are simple composite clocks each
> > > consisting of an input mux, divider and a gate.
> > >
> > > The VDEC_HEVC clock seems to have two paths similar to the VDEC_1 clock.
> > > However, the register offsets of the second clock path is not known.
> > > Amlogic's 3.10 kernel (which is used as reference) sets
> > > HHI_VDEC2_CLK_CNTL[31] to 1 before changing the VDEC_HEVC clock and back
> > > to 0 afterwards. For now, leave a TODO comment and only add the first
> > > path.
> > >
> >
> > Looking at aml-3.10/drivers/amlogic/amports/m8b/vdec_clk.c, it's weird
> > indeed. They seem to copy the divider's value to the same place
> > (HHI_VDEC2_CLK_CNTL[16~23]), and the only thing that stands out is
> > enabling HHI_VDEC2_CLK_CNTL[31].
> >
> > Then again they don't make use of that codepath at all, so who knows..
> indeed, that's why I skipped it for now
>
> [...]
> > > diff --git a/drivers/clk/meson/meson8b.h b/drivers/clk/meson/meson8b.h
> > > index e775f91ccce9..ed37196187e6 100644
> > > --- a/drivers/clk/meson/meson8b.h
> > > +++ b/drivers/clk/meson/meson8b.h
> > > @@ -37,6 +37,9 @@
> > >  #define HHI_MALI_CLK_CNTL              0x1b0 /* 0x6c offset in data sheet */
> > >  #define HHI_VPU_CLK_CNTL               0x1bc /* 0x6f offset in data sheet */
> > >  #define HHI_HDMI_CLK_CNTL              0x1cc /* 0x73 offset in data sheet */
> > > +#define HHI_VDEC_CLK_CNTL              0x1e0 /* 0x78 offset in data sheet */
> > > +#define HHI_VDEC2_CLK_CNTL             0x1e4 /* 0x79 offset in data sheet */
> > > +#define HHI_VDEC3_CLK_CNTL             0x1e8 /* 0x7a offset in data sheet */
> > >  #define HHI_NAND_CLK_CNTL              0x25c /* 0x97 offset in data sheet */
> > >  #define HHI_MPLL_CNTL                  0x280 /* 0xa0 offset in data sheet */
> > >  #define HHI_SYS_PLL_CNTL               0x300 /* 0xc0 offset in data sheet */
> > > @@ -156,8 +159,20 @@
> > >  #define CLKID_VPU_1_SEL                186
> > >  #define CLKID_VPU_1_DIV                187
> > >  #define CLKID_VPU_1            189
> > > +#define CLKID_VDEC_1_SEL       191
> > > +#define CLKID_VDEC_1_1_DIV     192
> > > +#define CLKID_VDEC_1_1         193
> > > +#define CLKID_VDEC_1_2_DIV     194
> > > +#define CLKID_VDEC_1_2         195
> >
> > In order to make use of the glitch-free mux by the driver, shouldn't
> > CLKID_VDEC_1_1 and CLKID_VDEC_1_2 be exported in the bindings ?
> I considered this but I didn't export them because of three reasons:
> - the video decoder driver doesn't have any logic to use the glitch-free mux yet
> - assigned-clock-rates or clk_set_rate will figure out the parent
> setup on it's own if we ignore the glitch-free mux until the video
> decoder driver supports it
> - exporting CLKIDs is easier than un-exporting them
>

Sure, makes sense. We'll revisit those in the future if we add on the
fly frequency adjusting to the vdec driver.

Reviewed-by: Maxime Jourdan <mjourdan@...libre.com>

> Regards
> Martin