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

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Message-ID: <eb0cbc41-2868-4cbf-9fbf-eeabd25dda04@omp.ru>
Date:   Fri, 10 Jun 2022 13:03:10 +0300
From:   Sergey Shtylyov <s.shtylyov@....ru>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Stephen Boyd <sboyd@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Michael Turquette <mturquette@...libre.com>,
        Luca Ceresoli <luca@...aceresoli.net>,
        Marek Vasut <marek.vasut@...il.com>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        <linux-clk@...r.kernel.org>, <linux-mips@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH v4 2/8] clk: vc5: Fix 5P49V6901 outputs disabling when
 enabling FOD

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/?

> 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@...kalelectronics.ru>

[...]

MBR, Sergey