Re: [PATCH 10/14] hw/misc/bcm2835_cprman: implement clock mux behaviour

From: Luc Michel <luc@lmichel.fr>
To: "Philippe Mathieu-Daudé" <f4bug@amsat.org>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	qemu-arm@nongnu.org, qemu-devel@nongnu.org,
	Andrew Baumann <Andrew.Baumann@microsoft.com>
Subject: Re: [PATCH 10/14] hw/misc/bcm2835_cprman: implement clock mux behaviour
Date: Sun, 4 Oct 2020 20:37:19 +0200	[thread overview]
Message-ID: <20201004183719.m3tsetxcgvc5ea2m@sekoia-pc.home.lmichel.fr> (raw)
In-Reply-To: <2ca8802e-3295-bd22-e705-931ae8dbbd1d@amsat.org>

On 16:51 Fri 02 Oct     , Philippe Mathieu-Daudé wrote:
> On 9/26/20 11:40 PM, Philippe Mathieu-Daudé wrote:
> > On 9/25/20 12:17 PM, Luc Michel wrote:
> >> A clock mux can be configured to select one of its 10 sources through
> >> the cm_ctl register. It also embeds yet another clock divider, composed
> >> of an integer part and a fractionnal part. The number of bits of each
> > 
> > Typo "fractional".
> > 
> >> part is mux dependant.
> > 
> > Typo "dependent"?
> > 
> >>
> >> Signed-off-by: Luc Michel <luc@lmichel.fr>
> >> ---
> >>  hw/misc/bcm2835_cprman.c | 43 +++++++++++++++++++++++++++++++++++++++-
> >>  1 file changed, 42 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/hw/misc/bcm2835_cprman.c b/hw/misc/bcm2835_cprman.c
> >> index 8df2db0fd9..75bc11939b 100644
> >> --- a/hw/misc/bcm2835_cprman.c
> >> +++ b/hw/misc/bcm2835_cprman.c
> >> @@ -229,19 +229,60 @@ static const TypeInfo cprman_pll_channel_info = {
> >>  };
> >>  
> >>  
> >>  /* clock mux */
> >>  
> >> +static bool clock_mux_is_enabled(CprmanClockMuxState *mux)
> >> +{
> >> +    return FIELD_EX32(*mux->reg_cm, CM_CLOCKx_CTL, ENABLE);
> >> +}
> >> +
> >>  static void clock_mux_update(CprmanClockMuxState *mux)
> >>  {
> >> -    clock_update(mux->out, 0);
> >> +    uint64_t freq, div;
> >> +    uint32_t src = FIELD_EX32(*mux->reg_cm, CM_CLOCKx_CTL, SRC);
> >> +    bool enabled = clock_mux_is_enabled(mux);
> >> +
> >> +    *mux->reg_cm = FIELD_DP32(*mux->reg_cm, CM_CLOCKx_CTL, BUSY, enabled);
> >> +
> >> +    if (!enabled) {
> >> +        clock_update(mux->out, 0);
> >> +        return;
> >> +    }
> >> +
> >> +    freq = clock_get_hz(mux->srcs[src]);
> >> +
> >> +    if (mux->int_bits == 0 && mux->frac_bits == 0) {
> >> +        clock_update_hz(mux->out, freq);
> >> +        return;
> >> +    }
> >> +
> >> +    /*
> >> +     * The divider has an integer and a fractional part. The size of each part
> >> +     * varies with the muxes (int_bits and frac_bits). Both parts are
> >> +     * concatenated, with the integer part always starting at bit 12.
> >> +     */
> >> +    div = mux->reg_cm[1] >> (R_CM_CLOCKx_DIV_FRAC_LENGTH - mux->frac_bits);
> >> +    div &= (1 << (mux->int_bits + mux->frac_bits)) - 1;
> 
> Eventually:
> 
>     div &= MAKE_64BIT_MASK(mux->int_bits + mux->frac_bits, 64);
I think this is MAKE_64BIT_MASK(0, mux->int_bits + mux->frac_bits)
(The shift macro parameter is 0 to have the ones positioned at the
mask's LSBs.
I'll use this macro in my next re-roll.

> 
> >> +
> >> +    freq = (freq << mux->frac_bits) / div;
> 
> Maybe:
> 
>     freq = muldiv64(freq, 1 << mux->frac_bits, div);
OK

> 
> >> +
> >> +    clock_update_hz(mux->out, freq);
> >>  }
> >>  
> >>  static void clock_mux_src_update(void *opaque)
> >>  {
> >>      CprmanClockMuxState **backref = opaque;
> >>      CprmanClockMuxState *s = *backref;
> >> +    CprmanClockMuxSource src = backref - s->backref;
> >> +    uint32_t current_src;
> 
> Maybe avoid current_src and use in place.
OK

> 
> Otherwise:
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Thanks !

-- 
Luc

> 
> >> +
> >> +    current_src = FIELD_EX32(*s->reg_cm, CM_CLOCKx_CTL, SRC);
> >> +
> >> +    if (current_src != src) {
> >> +        return;
> >> +    }
> >>  
> >>      clock_mux_update(s);
> >>  }
> >>  
> >>  static void clock_mux_init(Object *obj)
> >>
> > 

--