Subject: Re: REGRESSION: i2c-imx endlessly triggers clk warning

From: Russell King - ARM Linux admin <[email-masked]>
Date: Mon, 29 Jul 2019 12:26:57 +0100

On Mon, Jul 29, 2019 at 12:17:20PM +0100, Russell King - ARM Linux admin wrote:
> Booting 5.2 on the VF610 based ZII rev B board results in the board
> not making progress due to an endless stream of:
> 
> [  153.077831] ------------[ cut here ]------------
> [  153.082528] WARNING: CPU: 0 PID: 15 at drivers/clk/clk.c:924 clk_core_disable_lock+0x18/0x24
> [  153.093077] i2c0 already disabled
> [  153.096416] Modules linked in:
> [  153.099521] CPU: 0 PID: 15 Comm: kworker/0:1 Tainted: G        W         5.2.0+ #321
> [  153.107290] Hardware name: Freescale Vybrid VF5xx/VF6xx (Device Tree)
> [  153.113772] Workqueue: events deferred_probe_work_func
> [  153.118979] [<c0019560>] (unwind_backtrace) from [<c0014734>] (show_stack+0x10/0x14)
> [  153.126778] [<c0014734>] (show_stack) from [<c083f8dc>] (dump_stack+0x9c/0xd4)
> [  153.134051] [<c083f8dc>] (dump_stack) from [<c0031154>] (__warn+0xf8/0x124)
> [  153.141056] [<c0031154>] (__warn) from [<c0031248>] (warn_slowpath_fmt+0x38/0x48)
> [  153.148580] [<c0031248>] (warn_slowpath_fmt) from [<c040fde0>] (clk_core_disable_lock+0x18/0x24)
> [  153.157413] [<c040fde0>] (clk_core_disable_lock) from [<c058f520>] (i2c_imx_probe+0x554/0x6ec)
> [  153.166076] [<c058f520>] (i2c_imx_probe) from [<c04b9178>] (platform_drv_probe+0x48/0x98)
> [  153.174297] [<c04b9178>] (platform_drv_probe) from [<c04b7298>] (really_probe+0x1d8/0x2c0)
> [  153.182605] [<c04b7298>] (really_probe) from [<c04b7554>] (driver_probe_device+0x5c/0x174)
> [  153.190909] [<c04b7554>] (driver_probe_device) from [<c04b58c8>] (bus_for_each_drv+0x44/0x8c)
> [  153.199480] [<c04b58c8>] (bus_for_each_drv) from [<c04b746c>] (__device_attach+0xa0/0x108)
> [  153.207782] [<c04b746c>] (__device_attach) from [<c04b65a4>] (bus_probe_device+0x88/0x90)
> [  153.215999] [<c04b65a4>] (bus_probe_device) from [<c04b6a04>] (deferred_probe_work_func+0x60/0x90)
> [  153.225003] [<c04b6a04>] (deferred_probe_work_func) from [<c004f190>] (process_one_work+0x204/0x634)
> [  153.234178] [<c004f190>] (process_one_work) from [<c004f618>] (worker_thread+0x20/0x484)
> [  153.242315] [<c004f618>] (worker_thread) from [<c0055c2c>] (kthread+0x118/0x150)
> [  153.249758] [<c0055c2c>] (kthread) from [<c00090b4>] (ret_from_fork+0x14/0x20)
> [  153.257006] Exception stack(0xdde43fb0 to 0xdde43ff8)
> [  153.262095] 3fa0:                                     00000000 00000000 00000000 00000000
> [  153.270306] 3fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> [  153.278520] 3fe0: 00000000 00000000 00000000 00000000 00000013 00000000
> [  153.285159] irq event stamp: 3323022
> [  153.288787] hardirqs last  enabled at (3323021): [<c0861c4c>] _raw_spin_unlock_irq+0x24/0x2c
> [  153.297261] hardirqs last disabled at (3323022): [<c040d7a0>] clk_enable_lock+0x10/0x124
> [  153.305392] softirqs last  enabled at (3322092): [<c000a504>] __do_softirq+0x344/0x540
> [  153.313352] softirqs last disabled at (3322081): [<c00385c0>] irq_exit+0x10c/0x128
> [  153.320946] ---[ end trace a506731ccd9bd703 ]---
> 
> My guess is that this is due to a combination of e1ab9a468e3b ("i2c:
> imx: improve the error handling in i2c_imx_dma_request()") and the fact
> that my configuration has CONFIG_FSL_EDMA=m.  Given that the boot makes
> no progress, it seems that this driver now requires EDMA to be built-in
> _if_ this driver is also built in.  It seems that Kconfig allows an
> invalid configuration as far as the driver is concerned.
> 
> However, even though it seems that EDMA needs to be built-in with
> 5.2, this should not trigger the above kernel warning, which suggests
> something is wrong in the driver cleanup paths.

The endless loop is probably caused by the driver not obeying the basic
rule of: claim resources THEN publish APIs.  The driver registers
itself with the I2C core as an adapter (which then causes the child
devices to be created _and_ probed, thereby triggering the deferred
probing) only to fail later when trying to get DMA resources, and
returning -EPROBE_DEFER.  This causes the i2c-imx driver to be
immediately reprobed.

This driver really needs to obey the basic rule of drivers.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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