Re: [PATCH] clk: mxs: ensure that i.MX28's ref_io clks are not operated too fast

[Stefan Wahren <stefan.wahren@i2se.com>]

Hello Uwe,

Am 05.05.2017 um 09:25 schrieb Uwe Kleine-König:
> Hello Stefan,
>
> On Thu, May 04, 2017 at 02:25:07PM +0200, Stefan Wahren wrote:
>>        ref_io1                            1            1  
>> 320000000          0 0
> That means your ref_io1 is running at 320 MHz which my patch should
> prevent. Are you sure it is applied?

sorry for the mess in the dumps.

Your patch works fine regarding to ref_io1. I made 3 dumps:

1. without any patch ( ref_io1 320000000 )
2. with my ref_xtal patch ( ref_io1 288000000 )
3. with your patch ( ref_io1 288000000 )

I assume you looked at the wrong dump.

>  What is the register FRAC0
> (0x800401b0) set to? Given that ref_io1 is reported as running at
> 320000000 I'd expect that IO1FRAC is set to 27 which should be
> impossible with my patch given that clk_misc_init() in
> drivers/clk/mxs/clk-imx28.c initializes IO1FRAC0 to 30 and my patch
> should prevent it being set to something smaller than 30.
>
> Something I just noticed now is that the description of FRAC0 includes:
>
> 	NOTE: This register can only be addressed by byte instructions.
> 	Addressing word or half-word are not allowed.
>
> which is not respected by the clock driver.

I already tried it with no luck. Please follow the discussions [1] and [2].

Maybe the reason why [1] didn't work, was the missing memory barriers?

Please don't get me wrong, i'm very interested in fixing this issue.

Regards Stefan

[1] -
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/318644.html
[2] -
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-February/323720.html

>
> Best regards
> Uwe
>