Re: [PATCH 0/6] Add RZ/V2M Compare-Match Timer (TIM) support

[Rob Herring <robh@kernel.org>]

On Mon, Dec 05, 2022 at 02:59:49PM +0000, Biju Das wrote:
> This patch series aims to add support for Compare-Match Timer (TIM)
> module found on RZ/V2M SoC.
> 
> it is composed of 32 channels and channels 0-7 and 24-32 are
> reserved for ISP usage.
> 
> Channel 22 is modelled as clock source and Channel 23 is modelled as clock
> event driver and the rest of the channels are modelled as counter driver
> as it provides

Why did you pick those 2 counters for those functions?

Unless the h/w blocks are different, this is an abuse of compatible 
strings. What's the h/w difference that makes you care which counter the 
OS picks? That's what the DT should describe. If any timer will do, just 
let the OS pick.

> 
> 1) counter for counting
> 2) configurable counter value for generating timer interrupt
> 3) userspace event for each interrupt.
> 
> logs:-
> Counter driver:
> Counter driver is tested by reading counts and interrupts tested by
> counter-example in tools/counter/counter_example.c
> 
> Count snapshot value:
> 3114
> Output from counter_example when it triggers interrupts:
> Timestamp 0: 24142152969        Count 0: 5
> Error Message 0: Success
> 
> Clock source:
> Clock source driver is tested by clock-source-switch app.
> [ 1275.703567] clocksource: Switched to clocksource arch_sys_counter
> [ 1275.710189] clocksource: Switched to clocksource a4000b00.timer

Do you have any use case to really switch. Doing so disables the vDSO 
access to the clocksource.

Rob