Re: [PATCH 09/14] hw/misc/bcm2835_cprman: add a clock mux skeleton implementation

[Philippe Mathieu-Daudé]

On 10/2/20 4:42 PM, Philippe Mathieu-Daudé wrote:
> On 9/25/20 12:17 PM, Luc Michel wrote:
>> The clock multiplexers are the last clock stage in the cprman. Each mux
>> outputs one clock signal that goes out of the cprman to the SoC
>> peripherals.
>>
>> Each mux has at most 10 sources. The sources 0 to 3 are common to all
>> muxes. They are:
>>    0. ground (no clock signal)
>>    1. the main oscillator (xosc)
>>    2. "test debug 0" clock
>>    3. "test debug 1" clock
>>
>> Test debug 0 and 1 are actual clock muxes that can be used as sources to
>> other muxes (for debug purpose).
>>
>> Sources 4 to 9 are mux specific and can be unpopulated (grounded). Those
>> sources are fed by the PLL channels outputs.
>>
>> One corner case exists for DSI0E and DSI0P muxes. They have their source
>> number 4 connected to an intermediate multiplexer that can select
>> between PLLA-DSI0 and PLLD-DSI0 channel. This multiplexer is called
>> DSI0HSCK and is not a clock mux as such. It is really a simple mux from
>> the hardware point of view (see https://elinux.org/The_Undocumented_Pi).
>> This mux is not implemented in this commit.
>>
>> Note that there is some muxes for which sources are unknown (because of
>> a lack of documentation). For those cases all the sources are connected
>> to ground in this implementation.
>>
>> Each clock mux output is exported by the cprman at the qdev level,
>> adding the suffix '-out' to the mux name to form the output clock name.
>> (E.g. the 'uart' mux sees its output exported as 'uart-out' at the
>> cprman level.)
>>
>> Signed-off-by: Luc Michel <luc@lmichel.fr>
>> ---
[...]
>>  struct BCM2835CprmanState {
>>      /*< private >*/
>>      SysBusDevice parent_obj;
>>  
>>      /*< public >*/
>>      MemoryRegion iomem;
>>  
>>      CprmanPLLState plls[CPRMAN_NUM_PLL];
>>      CprmanPLLChannelState channels[CPRMAN_NUM_PLL_CHANNEL];
>> +    CprmanClockMuxState clock_muxes[CPRMAN_NUM_CLOCK_MUX];
>>  
>>      uint32_t regs[CPRMAN_NUM_REGS];
>>      uint32_t xosc_freq;
>>  
>>      Clock *xosc;
>> +    Clock *gnd;
> 
> This one seems to belong to MachineState in "hw/boards.h".

Although it might be easier to have a singleton in hw/core/clock.c...