[PATCH] kernel: x86: early-quirks: Replace mdelay with usleep_range in apple_airport_reset

[PATCH] kernel: x86: early-quirks: Replace mdelay with usleep_range in apple_airport_reset

[Jia-Ju Bai]

The function apple_airport_reset is not called in atomic context.
Thus mdelay can be replaced with usleep_range, to avoid busy wait.

This is reported by a static analysis tool named DCNS written by myself.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 arch/x86/kernel/early-quirks.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
index 1e82f78..559e81a 100644
--- a/arch/x86/kernel/early-quirks.c
+++ b/arch/x86/kernel/early-quirks.c
@@ -604,7 +604,7 @@ static void __init apple_airport_reset(int bus, int slot, int func)
 	if ((pmcsr & PCI_PM_CTRL_STATE_MASK) != PCI_D0) {
 		pmcsr &= ~PCI_PM_CTRL_STATE_MASK;
 		write_pci_config_16(bus, slot, func, BCM4331_PM_CAP + PCI_PM_CTRL, pmcsr);
-		mdelay(10);
+		usleep_range(10000, 11000);
 
 		pmcsr = read_pci_config_16(bus, slot, func, BCM4331_PM_CAP + PCI_PM_CTRL);
 		if ((pmcsr & PCI_PM_CTRL_STATE_MASK) != PCI_D0) {
-- 
1.7.9.5

Re: [PATCH] kernel: x86: early-quirks: Replace mdelay with usleep_range in apple_airport_reset

[Lukas Wunner]

On Wed, Jan 24, 2018 at 10:38:22AM +0800, Jia-Ju Bai wrote:
> The function apple_airport_reset is not called in atomic context.
> Thus mdelay can be replaced with usleep_range, to avoid busy wait.
> 
> This is reported by a static analysis tool named DCNS written by myself.

No, usleep_range() is built on hrtimers and at this point in the
boot sequence we haven't called hrtimers_init() yet.

Look at init/main.c:start_kernel() and note that setup_arch()
(which calls early_quirks()) is called way before hrtimers_init().

Please amend your static checker to consider every call to mdelay()
that occurs before hrtimers_init() a false positive, or manually
verify each patch for this constraint before submission.

I'll test your patch later today on my MacBook Pro but I suspect
it'll cause a boot crash or hang.  In any case the choice of mdelay()
here was deliberate.

Thanks,

Lukas

> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> ---
>  arch/x86/kernel/early-quirks.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
> index 1e82f78..559e81a 100644
> --- a/arch/x86/kernel/early-quirks.c
> +++ b/arch/x86/kernel/early-quirks.c
> @@ -604,7 +604,7 @@ static void __init apple_airport_reset(int bus, int slot, int func)
>  	if ((pmcsr & PCI_PM_CTRL_STATE_MASK) != PCI_D0) {
>  		pmcsr &= ~PCI_PM_CTRL_STATE_MASK;
>  		write_pci_config_16(bus, slot, func, BCM4331_PM_CAP + PCI_PM_CTRL, pmcsr);
> -		mdelay(10);
> +		usleep_range(10000, 11000);
>  
>  		pmcsr = read_pci_config_16(bus, slot, func, BCM4331_PM_CAP + PCI_PM_CTRL);
>  		if ((pmcsr & PCI_PM_CTRL_STATE_MASK) != PCI_D0) {
> -- 
> 1.7.9.5
> 

Re: [PATCH] kernel: x86: early-quirks: Replace mdelay with usleep_range in apple_airport_reset

[Andy Shevchenko]

On Wed, Jan 24, 2018 at 7:33 AM, Lukas Wunner <lukas@wunner.de> wrote:
> On Wed, Jan 24, 2018 at 10:38:22AM +0800, Jia-Ju Bai wrote:

> Please amend your static checker to consider every call to mdelay()
> that occurs before hrtimers_init() a false positive, or manually
> verify each patch for this constraint before submission.

> In any case the choice of mdelay() here was deliberate.

Perhaps, we need to put a comment for the next "Markus Elfring" crawler.

-- 
With Best Regards,
Andy Shevchenko