[PATCH v2 1/1] timer: imx-gpt: Add timer support for i.MX SoCs family

[Giulio Benetti]

Hi Jesse, Sean,

On 2/10/21 9:13 PM, Giulio Benetti wrote:
[SNIP]
>>    >
>>    >
>>    >> +    if ((int)rate <= 0) {
>>    >
>>    > This        ^^^^ is a cast trying to solve the problem above but it's
>>    > not correct. clk_get_rate() returns ulong, not int, so modify "int rate"
>>    > into "ulong rate".
>>    >
>>    >> +        dev_err(dev, "Could not get clock rate...\n");
>>    >> +        return -EINVAL;
>>    >> +    }
>>    >> +    /* Only support 24MHz clock */
>>    >
>>    > Extend to /* Only support 24MHz crystal clock */ otherwise it seems that
>>    > every 24Mhz clock is accepted and it's not that way.
>>    >
>>    > I don't know a sure way to be bounded to crystal clock, suggestions are
>>    > welcome.
>>
>> Why is it necessary? What are the constraints which require only using
>> the 24MHz reference?
> 
> To tell the truth there are no constraints, the reason is that I'm
> trying to keep this driver compatible and reusable by imx6* and imx7*
> since they setup the timer this way:
> https://gitlab.denx.de/u-boot/u-boot/-/blob/master/arch/arm/mach-imx/timer.c#L80-99
> 
> But if this timer needs to support any kind of clock source then let's
> modify it, but it gets more complicated and I think it could be done if
> needed.

This is the Linux way to make it work even if clock source is not 24Mhz:
https://github.com/torvalds/linux/blob/master/drivers/clocksource/timer-imx-gpt.c#L314-L329

It checks if clock source is 24Mhz and set CLKSRC(named V2_TPRER_PRE24M) 
to IPG_CLK_24M(named MXC_TPRER). Otherwise it uses peripheral clock and 
that's all.

At this point it's easier than I thought.

Jesse, can you please add that handling imitating Linux driver?

Best regards
-- 
Giulio Benetti
Benetti Engineering sas