Re: [PATCH v7 05/24] clocksource: Add a new timer-ingenic driver

On 24/09/2018 07:49, Paul Cercueil wrote:

Le 24 sept. 2018 07:35, Daniel Lezcano [off-list ref] a
écrit :

quoted

On 24/09/2018 07:24, Paul Cercueil wrote:

quoted

Hi Daniel,

Le 24 sept. 2018 05:12, Daniel Lezcano
[off-list ref] a écrit :

quoted

On 21/08/2018 19:16, Paul Cercueil wrote:

quoted

This driver handles the TCU (Timer Counter Unit) present on
the Ingenic JZ47xx SoCs, and provides the kernel with a
system timer, and optionally with a clocksource and a
sched_clock.

It also provides clocks and interrupt handling to client
drivers.

Can you provide a much more complete description of the timer
in order to make my life easier for the review of this patch?

See patch [03/24], it adds a doc file that describes the
hardware.

Thanks, I went through but it is incomplete to understand what the
timer do. I will reverse-engineer the code but it would help if you
can give the gross approach. Why multiple channels ? mutexes and
completion ?

Much of the complexity is because of the multi-purpose nature of the
TCU channels. Each one can be used as timer/clocksource, or PWM.

The driver starts by using channels 0 and 1 as system timer and
clocksource, respectively, the other ones being unused for now. Then,
*if* the PWM driver requests one of the channels in use by the
timer/clocksource driver, say channel 0, the timer/clocksource driver
will dynamically reassign the system timer to a free channel, from
channel 0 to e.g. channel 2. Only in that case the completion/mutex
are actually used.

Why do you need to do this? Can't be the channels dedicated and reserved
for clocksource and clockevent?


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