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

Le 24 sept. 2018 07:58, Daniel Lezcano [off-list ref] a écrit :

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

quoted

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? 

That's what I had in place (ingenic,timer-channel and ingenic,clocksource-channel DT properties), but Rob didn't want any linux-specific properties in the devicetree binding :(

-Paul