Re: Crashing 'kzm' target in next-20160913 due to 'gpio: mxc: shift gpio_mxc_init() to subsys_initcall level'

[Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>]

Hi Guenter,

On 09/14/2016 06:20 AM, Guenter Roeck wrote:
> Hi Vladimir,
>
> your commit e188cbf7564f ("gpio: mxc: shift gpio_mxc_init() to subsys_initcall level")
> in -next causes the following crash when running the 'kzm' target (and most likely
> the real thing) with qemu.
>
> [    1.211426] Unable to handle kernel NULL pointer dereference at virtual address 0000000c
> [    1.211600] pgd = c0004000
> [    1.211680] [0000000c] *pgd=00000000
> [    1.212067] Internal error: Oops: 5 [#1] SMP ARM
> [    1.212245] Modules linked in:
> [    1.212542] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.8.0-rc6-next-20160913 #1
> [    1.212671] Hardware name: Kyoto Microcomputer Co., Ltd. KZM-ARM11-01
> [    1.212825] task: c6848000 task.stack: c683e000
> [    1.213231] PC is at platform_get_irq+0xc0/0xe8
>
> See http://kerneltests.org/builders/qemu-arm-next/builds/525/steps/qemubuildcommand/logs/stdio
> for a complete log.
>
> Problem is quite subtle. The change causes the gpio driver to be installed later.
> As a result, kzm_init_smsc9118() fails to initialize the gpio pins correctly.
> gpio_request() in that function returns -EPROBE_DEFER, which is ignored,
> gpio_to_irq() then returns -22 which is unconditionally assigned as interrupt number.
> platform_get_irq(), as called from the smsc driver, gets this negative interrupt
> number, and passes it unconditionally to irq_get_irq_data(), which returns NULL.
> The NULL pointer is then passed to irqd_set_trigger_type() which, not entirely
> surprisingly, crashes.
>
> So, in other words, lots of bugs here. Nevertheless, I would suggest to keep using
> postcore_initcall(), at least until it is sure that all gpio clients handle -EPROBE_DEFER
> correctly.

I'm inviting Shawn and Uwe to the discussion.

The proper fix in this particular case should be like this one:

diff --git a/arch/arm/mach-imx/mach-kzm_arm11_01.c b/arch/arm/mach-imx/mach-kzm_arm11_01.c
index 31df4361996f..8288acfe7221 100644
--- a/arch/arm/mach-imx/mach-kzm_arm11_01.c
+++ b/arch/arm/mach-imx/mach-kzm_arm11_01.c
@@ -245,13 +245,17 @@ static void __init kzm_board_init(void)
  
  	mxc_iomux_setup_multiple_pins(kzm_pins,
  				      ARRAY_SIZE(kzm_pins), "kzm");
-	kzm_init_ext_uart();
-	kzm_init_smsc9118();
  	kzm_init_imx_uart();
  
  	pr_info("Clock input source is 26MHz\n");
  }
  
+static void __init kzm_late_init(void)
+{
+	kzm_init_ext_uart();
+	kzm_init_smsc9118();
+}
+
  /*
   * This structure defines static mappings for the kzm-arm11-01 board.
   */
@@ -291,5 +295,6 @@ MACHINE_START(KZM_ARM11_01, "Kyoto Microcomputer Co., Ltd. KZM-ARM11-01")
  	.init_irq = mx31_init_irq,
  	.init_time	= kzm_timer_init,
  	.init_machine = kzm_board_init,
+	.init_late	= kzm_late_init,
  	.restart	= mxc_restart,
  MACHINE_END
--

But I agree that there might be more legacy boards (i.MX31 only IMHO),
which may attempt to manipulate GPIO lines before subsys_initcall()
level.

Would it be better to move i.MX31 IOMUX controller driver under pinctrl
roof?

Any suggestions are welcome.

--
With best wishes,
Vladimir