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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 19 May 2021 20:17:16 +0200
Message-ID: <CAMuHMdWGakAT1LKg_sje=ZYTbLX1_BjjOsqOYP9KrzhMmMi6Ag@mail.gmail.com>
Subject: Re: [PATCH v7 0/5] clk: add driver for the SiFive FU740
To:     Zong Li <zong.li@sifive.com>
Cc:     Yixun Lan <yixun.lan@gmail.com>,
        Andreas Schwab <schwab@linux-m68k.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Pragnesh Patel <pragnesh.patel@openfive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Michael Turquette <mturquette@baylibre.com>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>,
        linux-clk <linux-clk@vger.kernel.org>,
        linux-riscv <linux-riscv@lists.infradead.org>
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Hi Zong,

On Wed, May 19, 2021 at 5:55 PM Zong Li <zong.li@sifive.com> wrote:
> On Tue, May 11, 2021 at 4:57 PM Yixun Lan <yixun.lan@gmail.com> wrote:
> > On Wed, Apr 14, 2021 at 2:25 PM Zong Li <zong.li@sifive.com> wrote:
> > > On Mon, Apr 12, 2021 at 7:31 PM Andreas Schwab <schwab@linux-m68k.org> wrote:
> > > > On Mär 31 2021, Zong Li wrote:
> > > > > I found that the gemgxlpll was disabled immediately by power
> > > > > management after macb driver install. The mainline's defconfig doesn't
> > > > > enable CONFIG_PM, so the network is fine on it. The opensuse defconfig
> > > > > enables CONFIG_PM, and the patch
> > > > > 732374a0b440d9a79c8412f318a25cd37ba6f4e2 added the enable/disable
> > > > > callback functions, so the gemgxlpll PLL, I have no idea why power
> > > > > management disable it, I would keep trace it.
> > > >
> > > > Does that mean that CONFIG_PM also affects the FU740?
> > >
> > > Yes, we got the same problem on the FU740. We are checking the issue.
> > >
> > Just a mild ping, any progress regarding this issue?
>
> Currently, if runtime power management is enabled, macb driver would
> go to sleep at the end of macb_probe, then the gigabit ethernet PLL
> would be disabled.  During this period of time, the system would hang
> up if we try to access GEMGXL control registers, it means that we
> can't access GEMGXL control registers before the gigabit ethernet PLL
> is resumed again. There are some cases, for example, if we execute the

Sounds familiar.

> 'ifconfig' command, it would eventually go to the macb_get_status to

Do you mean mac_get_stats()? macb_get_status() does not exist.

> access GEMGXL control registers and cause the system to hang up. Give
> more example here, if we execute 'ip link set lo up & ip addr add
> 127.0.0.1/8 dev lo', it would cause the system to hang up, because
> these commands would try to query the interfaces and eventually go to
> macb_get_status as well. However, if we can resume the gigabit
> ethernet PLL first, such as 'ip link set eth0 up' or 'udhcpc', then
> everything goes well. I'm trying to figure out if there are some hooks
> that we can check the PLL status in the macb driver before it actually
> touches the control registers. If anyone has an idea about that,
> please feel free to point it out to me, thanks.

And you cannot call pm_runtime_get_sync(), as this is called from
atomic contect. Other drivers avoid accessing the registers while
the device is not up, cfr. e.g. commit 7fa2955ff70ce453 ("sh_eth:
Fix sleeping function called from invalid context").

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds