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

[Philippe Mathieu-Daudé]

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);

>> +
>> +    freq = (freq << mux->frac_bits) / div;

Maybe:

    freq = muldiv64(freq, 1 << mux->frac_bits, div);

>> +
>> +    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.

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

>> +
>> +    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)
>>
>