linux-kernel - Re: [RFC PATCH v4 7/8] pwm: Add dummy pwmchip for orphan pwms

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Date:   Tue, 17 Oct 2017 14:40:31 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Jeffy Chen <jeffy.chen@...k-chips.com>
Cc:     linux-kernel@...r.kernel.org, dmitry.torokhov@...il.com,
        heiko@...ech.de, briannorris@...omium.org, rjw@...ysocki.net,
        dianders@...omium.org, tfiga@...omium.org, broonie@...nel.org,
        seanpaul@...omium.org, linux-pwm@...r.kernel.org
Subject: Re: [RFC PATCH v4 7/8] pwm: Add dummy pwmchip for orphan pwms

On Tue, Oct 17, 2017 at 06:16:23PM +0800, Jeffy Chen wrote:
> When the pwm driver is unbound while the pwm is still requested, the
> pwm core would not actually remove the pwmchip(return -EBUSY instead).
> 
> So it would hold some references to the invalid resources(e.g. pwmchip).
> 
> And the customer who requested the pwm would have those references too,
> and may crash the kernel when trying to access them later.
> 
> Add a dummy pwmchip, and assign orphan pwms to it to avoid that.
> 
> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> ---
> 
> Changes in v4:
> Fix compile warning.
> 
> Changes in v3:
> Assign orphan pwms to dummy pwmchip instead of adding device link in the
> customer driver.

What happened to this? Device links were specifically designed to avoid
situations like these.

A dummy PWM chip doesn't seem like the right solution to this.

Thierry

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