linux-kernel - Re: [PATCH v7 10/42] clk: davinci: New driver for davinci PSC clocks

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Date:   Wed, 28 Feb 2018 15:40:40 -0600
From:   David Lechner <david@...hnology.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     linux-clk@...r.kernel.org,
        linux-devicetree <devicetree@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>,
        Adam Ford <aford173@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 10/42] clk: davinci: New driver for davinci PSC clocks

On 02/28/2018 06:38 AM, Bartosz Golaszewski wrote:
> 
> I think I found the reason for the strange crashes we were
> experiencing (emac core->name being NULL) thanks to Sekhar who pointed
> me in the right direction.
> 
> The mdio driver fails to probe with v7 due to the supplied clock rate
> being wrong. Before failing we register the emac clock with
> pm_clk_add_clk(). When clock_ops puts the clock, it decreases the
> reference count of the clock, but we never actually increased it in
> the first place in the line above. The core clock code then destroys
> the associated clk_core structure. When the next user comes around (in
> our case the clk debug functions) the system crashes.
> 
> I believe there to be two issues: one is with v7 - we need to increase
> the clock reference count in davinci_psc_genpd_attach_dev().
> 
> Second is the error path in the clock framework - we should remove the
> destroyed clk_core from the debug list, which is not being done now.
> 
> Why we even need to track the refcount of clk_core is a mistery for me
> though. Stephen, Mike?
> 
> Best regards,
> Bartosz Golaszewski

Great find. I figured it had to be something like this, but I wasn't
able to reproduce the problem yet.

I suppose it is time to spin up a v8 with some fixes.