linux-kernel - Re: [PATCH] pnp: Bypass the calling to pnp_stop_dev at suspend when there is a protocol suspend

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Date:	Mon, 06 Jan 2014 09:20:51 +0800
From:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
To:	shuox.liu@...el.com, rafael.j.wysocki@...el.com
Cc:	linux-kernel@...r.kernel.org, bhelgaas@...gle.com,
	yanmin.zhang@...el.com
Subject: Re: [PATCH] pnp: Bypass the calling to pnp_stop_dev at suspend when
 there is a protocol suspend

On 二, 2013-12-24 at 09:35 +0800, shuox.liu@...el.com wrote:
> From: Zhang Yanmin <yanmin.zhang@...el.com>
> 
> pnp pnp_bus_suspend/_resume have an issue.
> pnp_bus_suspend calls pnp_stop_dev to disable the device. With ACPI,
> pnp_stop_dev turns off the dev usually. Then,
> pnp_bus_suspend=>pnp_dev->protocol->suspend accesses the device and
> suspend it again.
> 
> pnp_bus_resume has the similar issue.
> 
> Another issue is firmware might just provide _DIS, but no_STS method.
> 
> The patch fixes it by adding a checking. If there is
> pnp_dev->protocol->suspend, pnp_bus_suspend doesn't call pnp_stop_dev.
> Do the similar thing for _resume.
Rafael,

What's your idea about this patch?

We hit the issue when enabling Android on a latest tablet. After
suspend-to-ram wakeup, serial console doesn't work.
This serial port is bound by pnpcore driver.
At suspending, 
static int __pnp_bus_suspend(struct device *dev, pm_message_t state)
{
	...

        if (pnp_can_disable(pnp_dev)) {
                error = pnp_stop_dev(pnp_dev);
                if (error)
                        return error;
        }

        if (pnp_dev->protocol->suspend)
                pnp_dev->protocol->suspend(pnp_dev, state);
        return 0;
}

pnp_stop_dev calls dev->protocol->disable.
As for ACPI device, that disable callback calls _DIS. Based
on ACPI spec, driver need turn off the device before disabling it
by _DIS. That means, after pnp_stop_dev returns, the device is at OFF
state.

Then, __pnp_bus_suspend calls pnp_dev->protocol->suspend, which
continues to access the device while the device is at OFF.

Our firmware just provides _DIS for the device. There is no _STS
method. Then, after wakeup, the device doesn't work.

But just like what the patch points out, pnp_dev->protocol->suspend
continues to access the device while the device is at OFF. It's not safe.

The patch looks like a workaround. Another possible fix is to just
delete the calling of pnp_stop_dev in function __pnp_bus_suspend, as
suspend is not equal to _disable_.
The deletion might be a little intrusive. That's why we sent a workaround
patch to LKML.

Which one is better?

Thanks,
Yanmin

> 
> Signed-off-by: Zhang Yanmin <yanmin.zhang@...el.com>
> Signed-off-by: Liu ShuoX <shuox.liu@...el.com>
> ---
>  drivers/pnp/driver.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pnp/driver.c b/drivers/pnp/driver.c
> index f748cc8..2512e47 100644
> --- a/drivers/pnp/driver.c
> +++ b/drivers/pnp/driver.c
> @@ -176,7 +176,7 @@ static int __pnp_bus_suspend(struct device *dev, pm_message_t state)
>  			return error;
>  	}
>  
> -	if (pnp_can_disable(pnp_dev)) {
> +	if (pnp_can_disable(pnp_dev) && !pnp_dev->protocol->suspend) {
>  		error = pnp_stop_dev(pnp_dev);
>  		if (error)
>  			return error;
> @@ -215,9 +215,7 @@ static int pnp_bus_resume(struct device *dev)
>  		error = pnp_dev->protocol->resume(pnp_dev);
>  		if (error)
>  			return error;
> -	}
> -
> -	if (pnp_can_write(pnp_dev)) {
> +	} else if (pnp_can_write(pnp_dev)) {
>  		error = pnp_start_dev(pnp_dev);
>  		if (error)
>  			return error;


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