linux-kernel - RE: [1/1] i2c: designware: Ensure runtime suspend is invoked during rapid slave unregistration and registration

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Message-ID:
 <NTZPR01MB1018FD0E9913437D4B34E751F88B2@NTZPR01MB1018.CHNPR01.prod.partner.outlook.cn>
Date: Thu, 8 May 2025 08:30:27 +0000
From: EnDe Tan <ende.tan@...rfivetech.com>
To: Andi Shyti <andi.shyti@...nel.org>, Jarkko Nikula
	<jarkko.nikula@...ux.intel.com>
CC: "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>,
	"mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
	"jsd@...ihalf.com" <jsd@...ihalf.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Leyfoon Tan <leyfoon.tan@...rfivetech.com>,
	"endeneer@...il.com" <endeneer@...il.com>
Subject: RE: [1/1] i2c: designware: Ensure runtime suspend is invoked during
 rapid slave unregistration and registration

Hi Andi and Jarkko, thank you for the feedback.

> -----Original Message-----
> From: Andi Shyti <andi.shyti@...nel.org>
> Sent: Tuesday, 6 May, 2025 5:49 AM
> To: Jarkko Nikula <jarkko.nikula@...ux.intel.com>
> Cc: EnDe Tan <ende.tan@...rfivetech.com>; linux-i2c@...r.kernel.org;
...
> > Good explanation and could you add it the commit log together with the
> > example?
> 
> If you want you can paste the new commit log as reply to this e-mail.

Here is the new commit log, feel free to let me know if further changes are required:

Replaced pm_runtime_put() with pm_runtime_put_sync_suspend() to ensure
the runtime suspend is invoked immediately when unregistering a slave.
This prevents a race condition where suspend was skipped when
unregistering and registering slave in quick succession.

For example, consider the rapid sequence of
`delete_device -> new_device -> delete_device -> new_device`.
In this sequence, it is observed that the dw_i2c_plat_runtime_suspend() might
not be invoked after `delete_device` operation.

This is because after `delete_device` operation, when the
pm_runtime_put() is about to trigger suspend, the following `new_device`
operation might race and cancel the suspend.

If that happens, during the `new_device` operation,
dw_i2c_plat_runtime_resume() is skipped (since there was no suspend), which
means `i_dev->init()`, i.e. i2c_dw_init_slave(), is skipped.
Since i2c_dw_init_slave() is skipped, i2c_dw_configure_fifo_slave() is
skipped too, which leaves `DW_IC_INTR_MASK` unconfigured. If we inspect
the interrupt mask register using devmem, it will show as zero.

Example shell script to reproduce the issue:
```
  #!/bin/sh

  SLAVE_LADDR=0x1010
  SLAVE_BUS=13
  NEW_DEVICE=/sys/bus/i2c/devices/i2c-$SLAVE_BUS/new_device
  DELETE_DEVICE=/sys/bus/i2c/devices/i2c-$SLAVE_BUS/delete_device

  # Create initial device
  echo slave-24c02 $SLAVE_LADDR > $NEW_DEVICE
  sleep 2

  # Rapid sequence of
  # delete_device -> new_device -> delete_device -> new_device
  echo $SLAVE_LADDR > $DELETE_DEVICE
  echo slave-24c02 $SLAVE_LADDR > $NEW_DEVICE
  echo $SLAVE_LADDR > $DELETE_DEVICE
  echo slave-24c02 $SLAVE_LADDR > $NEW_DEVICE

  # Using devmem to inspect IC_INTR_MASK will show as zero
```