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

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

On 10/4/20 9:34 PM, Luc Michel wrote:
> On 16:42 Fri 02 Oct     , 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>
>>> ---
>>>  include/hw/misc/bcm2835_cprman.h           |  84 ++++
>>>  include/hw/misc/bcm2835_cprman_internals.h | 421 +++++++++++++++++++++
>>>  hw/misc/bcm2835_cprman.c                   | 151 ++++++++
>>>  3 files changed, 656 insertions(+)
>>>
>>> diff --git a/include/hw/misc/bcm2835_cprman.h b/include/hw/misc/bcm2835_cprman.h
>>> index aaf15fb20c..c2a89e8e90 100644
>>> --- a/include/hw/misc/bcm2835_cprman.h
>>> +++ b/include/hw/misc/bcm2835_cprman.h
>>> @@ -52,12 +52,73 @@ typedef enum CprmanPLLChannel {
>>>      CPRMAN_PLLH_CHANNEL_PIX,
>>>
>>>      CPRMAN_PLLB_CHANNEL_ARM,
>>>
>>>      CPRMAN_NUM_PLL_CHANNEL,
>>> +
>>> +    /* Special values used when connecting clock sources to clocks */
>>> +    CPRMAN_CLOCK_SRC_NORMAL = -1,
>>> +    CPRMAN_CLOCK_SRC_FORCE_GROUND = -2,
>>> +    CPRMAN_CLOCK_SRC_DSI0HSCK = -3,
>>
>> Why not use CPRMAN_NORMAL_CHANNEL,
>> CPRMAN_FORCED_GROUND_CHANNEL and CPRMAN_DSI0HSCK_CHANNEL?
> Well, those are special values used when connecting the clock sources to
> the muxes in connect_mux_sources(). They are not channels hence the
> name. To keep the code simple, I reused the CprmanPLLChannel type for
> mux sources (it is used in bcm2835_cprman_internals.h to describe what
> source connects to what mux input).
> 
> Ideally this type should be named something like ClockMuxSources (and
> CprmanPLLChannel should be a sub-set of this type). But doing so
> complicates the code quite a bit so I chose to simply have those three
> constants here instead.

Understood, OK.