Re: [PATCH v4 2/8] clk: vc5: Fix 5P49V6901 outputs disabling when enabling FOD

Serge Semin
2022-06-10T10:24:50Z

On Fri, Jun 10, 2022 at 01:03:10PM +0300, Sergey Shtylyov wrote:
> On 6/10/22 10:21 AM, Serge Semin wrote:
>
> > We have discovered random glitches during the system boot up procedure.
> > The problem investigation led us to the weird outcomes: when none of the
> > Renesas 5P49V6901 ports are explicitly enabled by the kernel driver, the
> > glitches disappeared. It was a mystery since the SoC external clock
> > domains were fed with different 5P49V6901 outputs. The driver code didn't
> > seem like bogus either. We almost despaired to find out a root cause when
> > the solution was found for a more modern revision of the chip. It turned
> > out the 5P49V6901 clock generator stopped its output for a short period of
> > time during the VC5_OUT_DIV_CONTROL register writing. The same problem has
> > was found for the 5P49V6965 revision of the chip and the was successfully
>

> s/was found/been found/, s/the was/that was/?

Right. Thanks.)

-Sergey

>
> > fixed in commit fc336ae622df ("clk: vc5: fix output disabling when
> > enabling a FOD") by enabling the "bypass_sync" flag hidden inside "Unused
> > Factory Reserved Register". Even though the 5P49V6901 registers
> > description and programming guide doesn't provide any intel regarding that
> > flag, setting it up anyway in the officially unused register completely
> > eliminated the denoted glitches. Thus let's activate the functionality
> > submitted in commit fc336ae622df ("clk: vc5: fix output disabling when
> > enabling a FOD") for the Renesas 5P49V6901 chip too in order to remove
> > the ports implicit inter-dependency.
> >
> > Fixes: dbf6b16f5683 ("clk: vc5: Add support for IDT VersaClock 5P49V6901")
> > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
>
> [...]
>
> MBR, Sergey