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Re: [PATCH 09/14] hw/misc/bcm2835_cprman: add a clock mux skeleton imple
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [PATCH 09/14] hw/misc/bcm2835_cprman: add a clock mux skeleton implementation |
Date: |
Sun, 4 Oct 2020 22:17:41 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 |
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.