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

[Luc Michel <luc@lmichel.fr>]

On 20:37 Sun 04 Oct     , Luc Michel wrote:
> 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.
Actually, I won't, because switching to muldiv64 implied some
modifications. The muldiv64 divisor parameter is uint32_t. Since there
is no MAKE_32BIT_MASK, and I don't use all the "features" of this macro
anyway (shift = 0 in my case), I'll keep this form (but I'll switch to
uin32_t for div).

-- 
Luc

> 
> > 
> > >> +
> > >> +    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)
> > >>
> > > 
> 
> -- 

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