Re: [PATCH V2 2/6] clocksource: tegra: add Tegra210 timer driver

From: Joseph Lo
Date: Tue Jan 29 2019 - 21:40:13 EST

On 1/29/19 6:29 PM, Thierry Reding wrote:
On Tue, Jan 29, 2019 at 10:41:55AM +0200, Peter De Schrijver wrote:
On Mon, Jan 28, 2019 at 04:09:08PM +0100, Thierry Reding wrote:


Up to here this is a duplicate of timer-tegra20.c. And a lot of
tegra210_timer_init() is the same as tegra20_timer_init() as well. Can't
we unify the two drivers instead?

The power cycle restrictions of the architected timer, do they not apply
to chips earlier than Tegra210 either? So don't we need all of these
additional features on the timer-tegra20.c driver as well? If so that

No. Chips prior to Tegra114 do not have an arch timer and the arch timer
does work correctly on Cortex-A15 so Tegra114 and Tegra124 can use it.
It's broken on Cortex-A57 though, so we can't use it as a wakeup source
on Tegra210.

If chips prior to Tegra114 don't have an architected timer, then we
can't remove the timer-tegra20 driver, because we still need it on
Tegra20 and Tegra30, right?

For Tegra20/30, it's Cortext-A9 with TWD timer. (arch/arm/kernel/smp_twd.c)

Originally, I thought the functionality of timer-tegra20 would be fully replaced by TWD timer driver. But from the log in the kernelci test farm[1][2], it looks to me the timer-tegra20 driver still works as clocksource driver for Tegra20/30. I cannot confirm if the clock event device has been replaced by TWD timer in the log. It could be replaced in the background. And by looking into the driver, it should be.

Compare to the log of Tegra124[3], it has been fully replaced by arch timer driver.

Note, "timer_us" is the name of Tegra20 timer.