Date:   Sat, 4 May 2019 08:01:30 -0300
From:   Fabio Estevam <festevam@...il.com>
To:     Kay-Liu <liuk@...ca.net.cn>
Cc:     Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Sascha Hauer <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        Yongcai Huang <Anson.Huang@....com>,
        Rob Herring <robh@...nel.org>,
        root <root@...alhost.localdomain>, tiny.windzz@...il.com,
        linux-clk <linux-clk@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 2/2] clk: imx6sx: Remove unexisting IMX6SX_CLK_ENET_AHB clock

Hi Kay-Liu,

On Thu, Apr 25, 2019 at 8:14 AM <liuk@...ca.net.cn> wrote:
>
> From: Kay-Liu <liuk@...ca.net.cn>
>
> The imx6sx's dts file defines five clocks for fec, the
> 'ahb'clock's value is IMX6SX_CLK_ENET_AHB, but in the
> i.MX6SX Reference Manual there is no such enet ahb clock,
> there is only one "enet clock" in the CCM_CCGR3 register
> which is controlled by bits 5-4, the enet clock is defined
> for the 'ipg' clock, this can cause problem.
> The original phenomenon is using imx6-solox processor and
> Marvel 88E6390 switch with linux OS, the kernel will hang
> during the startup of the linux OS.
> After analyzing the phenomenon, the reason of CPU hang is
> read/write enet module's register when the enet clock
> is disabled. The kernel code try to avoids the problem
> by resume enet clock before read/write enet register.
> But the enet module's clock config will cause a special
> environment which can bypass the clock resume mechanism.
> The CPU has only one enet clock, after kernel parses
> the dts file, the two clock variables 'ipg' and 'ahb'
> finnaly point to the same enet clock register. This will
> cause enet clock be disabled after fec probe over.
> Because the power saving module will affect the BUG, so
> there are two situations for this problem:
> 1)Turn off power saving
> Turn off power saving means that the resume mechanism is
> disabled, so after fec probe over if any one read/write
> enet module's register, the CPU will hang because no one
> could resume the enet clock.
> 2)Turn on power saving
> Turn on power saving could resume enet clock before
> read/write enet register by enable 'ipg' clk, this will
> cause 'ahb' variable state and enet clock register value
> don't match.If any task read/write enet at a high
> frequently, the kernel will keep resume state and never
> enter suspend process, this means that the kernel will
> only modifies the register value during the first resume.
> But the kernel init will check unused clock variable in
> the late initcall, the 'ahb' clock will be treated as
> unused, at this time, the enet clock will be disabled
> bypass the resume mechanism, then the next read/write
> enet module's register will cause the CPU hang.
> Proposed solution is delete the 'ahb' clock's definition
> in the clk-imx6sx.c, and modify fec device’s clocks in
> the dts file, point ‘ahb’ from IMX6SX_CLK_ENET_AHB to
> IMX6SX_CLK_ENET
>
> Signed-off-by: Kay-Liu <liuk@...ca.net.cn>

This matches the mx6sx reference manual:

Reviewed-by: Fabio Estevam <festtevam@...il.com>

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