linux-kernel - Re: [PATCH 1/2] i2c: designware: Avoid taking clk

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Message-ID: <7198221a-1f12-49cf-9d35-7498ae7389cd@linux.intel.com>
Date: Thu, 21 Aug 2025 15:45:43 +0300
From: Jarkko Nikula <jarkko.nikula@...ux.intel.com>
To: Jisheng Zhang <jszhang@...nel.org>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>,
 Jan Dabros <jsd@...ihalf.com>, Andi Shyti <andi.shyti@...nel.org>,
 linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH 1/2] i2c: designware: Avoid taking clk_prepare mutex in PM
 callbacks

On 8/20/25 7:33 PM, Jisheng Zhang wrote:
> On Wed, Aug 20, 2025 at 07:05:42PM +0300, Andy Shevchenko wrote:
>> On Wed, Aug 20, 2025 at 11:31:24PM +0800, Jisheng Zhang wrote:
>>> This is unsafe, as the runtime PM callbacks are called from the PM
>>> workqueue, so this may deadlock when handling an i2c attached clock,
>>> which may already hold the clk_prepare mutex from another context.
>>
>> Can you be more specific? What is the actual issue in practice?
>> Do you have traces and lockdep warnings?
> 
> Assume we use i2c designware to control any i2c based clks, e.g the
> clk-si5351.c driver. In its .clk_prepare, we'll get the prepare_lock
> mutex, then we call i2c adapter to operate the regs, to runtime resume
> the i2c adapter, we call clk_prepare_enable() which will try to get
> the prepare_lock mutex again.
> 
I'd also like to see the issue here. I'm blind to see what's the 
relation between the clocks managed by the clk-si5351.c and clocks to 
the i2c-designware IP.