[PATCH] ARM: imx6: Fix "BUG: scheduling while atomic" if PCIe switch is attached

[PATCH] ARM: imx6: Fix "BUG: scheduling while atomic" if PCIe switch is attached

[David Müller]

This problem has already been reported as 
https://bugzilla.kernel.org/show_bug.cgi?id=100031

Signed-off-by: David Müller <dave.mueller@gmx.ch>
---
 drivers/pci/host/pci-imx6.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
index fdb9536..c63691c 100644
--- a/drivers/pci/host/pci-imx6.c
+++ b/drivers/pci/host/pci-imx6.c
@@ -489,7 +489,7 @@ static int imx6_pcie_link_up(struct pcie_port *pp)
 		 * Wait a little bit, then re-check if the link finished
 		 * the training.
 		 */
-		usleep_range(1000, 2000);
+		mdelay(20);
 	}
 	/*
 	 * From L0, initiate MAC entry to gen2 if EP/RC supports gen2.
-- 
1.8.4

Re: [PATCH] ARM: imx6: Fix "BUG: scheduling while atomic" if PCIe switch is attached

[Lucas Stach]

Am Donnerstag, den 18.06.2015, 09:56 +0200 schrieb David Müller:
> This problem has already been reported as 
> https://bugzilla.kernel.org/show_bug.cgi?id=100031
> 
> Signed-off-by: David Müller <dave.mueller@gmx.ch>
> ---
>  drivers/pci/host/pci-imx6.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
> index fdb9536..c63691c 100644
> --- a/drivers/pci/host/pci-imx6.c
> +++ b/drivers/pci/host/pci-imx6.c
> @@ -489,7 +489,7 @@ static int imx6_pcie_link_up(struct pcie_port *pp)
>  		 * Wait a little bit, then re-check if the link finished
>  		 * the training.
>  		 */
> -		usleep_range(1000, 2000);
> +		mdelay(20);

While switching to mdelay might be the right thing to do here, you are
also changing the timeout. This is a change in behavior and so not okay.
Especially as you keep the CPU spinning for the duration of that
timeout.
 
>  	}
>  	/*
>  	 * From L0, initiate MAC entry to gen2 if EP/RC supports gen2.

-- 
Pengutronix e.K.             | Lucas Stach                 |
Industrial Linux Solutions   | http://www.pengutronix.de/  |

Re: [PATCH] ARM: imx6: Fix "BUG: scheduling while atomic" if PCIe switch is attached

[Fabio Estevam]

On Thu, Jun 18, 2015 at 5:27 AM, Lucas Stach <l.stach@pengutronix.de> wrote:

>> diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
>> index fdb9536..c63691c 100644
>> --- a/drivers/pci/host/pci-imx6.c
>> +++ b/drivers/pci/host/pci-imx6.c
>> @@ -489,7 +489,7 @@ static int imx6_pcie_link_up(struct pcie_port *pp)
>>                * Wait a little bit, then re-check if the link finished
>>                * the training.
>>                */
>> -             usleep_range(1000, 2000);
>> +             mdelay(20);
>
> While switching to mdelay might be the right thing to do here, you are
> also changing the timeout. This is a change in behavior and so not okay.

msleep(2) is not recommended according to Documentation/timers/timers-howto.txt.

What would be the proper fix then?

Regards,

Fabio Estevam
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Re: [PATCH] ARM: imx6: Fix "BUG: scheduling while atomic" if PCIe switch is attached

[Lucas Stach]

Am Montag, den 22.06.2015, 10:30 -0300 schrieb Fabio Estevam:
> On Thu, Jun 18, 2015 at 5:27 AM, Lucas Stach <l.stach@pengutronix.de> wrote:
> 
> >> diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
> >> index fdb9536..c63691c 100644
> >> --- a/drivers/pci/host/pci-imx6.c
> >> +++ b/drivers/pci/host/pci-imx6.c
> >> @@ -489,7 +489,7 @@ static int imx6_pcie_link_up(struct pcie_port *pp)
> >>                * Wait a little bit, then re-check if the link finished
> >>                * the training.
> >>                */
> >> -             usleep_range(1000, 2000);
> >> +             mdelay(20);
> >
> > While switching to mdelay might be the right thing to do here, you are
> > also changing the timeout. This is a change in behavior and so not okay.
> 
> msleep(2) is not recommended according to Documentation/timers/timers-howto.txt.
> 
> What would be the proper fix then?
> 
mdelay(2) is completely reasonable. Note the difference between delay
and sleep.

The mid-term correct solution would be to move all the link-up handling
out of the atomic path.

Regards,
Lucas
-- 
Pengutronix e.K.             | Lucas Stach                 |
Industrial Linux Solutions   | http://www.pengutronix.de/  |

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Re: [PATCH] ARM: imx6: Fix "BUG: scheduling while atomic" if PCIe switch is attached

[Fabio Estevam]

On Mon, Jun 22, 2015 at 10:37 AM, Lucas Stach <l.stach@pengutronix.de> wrote:

> mdelay(2) is completely reasonable. Note the difference between delay
> and sleep.

Oh, that's right :-)

Thanks
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Re: [PATCH] ARM: imx6: Fix "BUG: scheduling while atomic" if PCIe switch is attached

[Bjorn Helgaas]

On Thu, Jun 18, 2015 at 09:56:54AM +0200, David Müller wrote:
> This problem has already been reported as 
> https://bugzilla.kernel.org/show_bug.cgi?id=100031
> 
> Signed-off-by: David Müller <dave.mueller@gmx.ch>
> ---
>  drivers/pci/host/pci-imx6.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
> index fdb9536..c63691c 100644
> --- a/drivers/pci/host/pci-imx6.c
> +++ b/drivers/pci/host/pci-imx6.c
> @@ -489,7 +489,7 @@ static int imx6_pcie_link_up(struct pcie_port *pp)
>  		 * Wait a little bit, then re-check if the link finished
>  		 * the training.
>  		 */
> -		usleep_range(1000, 2000);
> +		mdelay(20);
>  	}
>  	/*
>  	 * From L0, initiate MAC entry to gen2 if EP/RC supports gen2.

I asked in the bugzilla why imx6_pcie_link_up() looks nothing like the
other pcie_host_ops.link_up() methods.

Lucas responded:
> the i.MX6 link up routine is a bit more complex compared to the other
> designware drivers because of a hardware bug, where some FIFOs could
> get out of sync when changing the link speed. We need to start the
> link at Gen1, wait for it to be stable, then start a directed link
> speed change if the EP is Gen2 and wait for the link to be stable
> again. If the link doesn't come back, we need to start over.

> I don't think any of the other DW PCIe implementations need this
> workaround.

That explanation makes sense, and a comment to that effect should be
in the code.  But I also wonder whether this workaround could be moved
to imx6_pcie_start_link() (just renamed to imx6_pcie_establish_link()).
Then imx6_pcie_link_up() could be a simple status check like the
others.

Bjorn

Re: [PATCH] ARM: imx6: Fix "BUG: scheduling while atomic" if PCIe switch is attached

[Bjorn Helgaas]

On Thu, Jun 18, 2015 at 09:56:54AM +0200, David Müller wrote:
> This problem has already been reported as 
> https://bugzilla.kernel.org/show_bug.cgi?id=100031
> 
> Signed-off-by: David Müller <dave.mueller@gmx.ch>

Dropping for now, hoping for an update addressing the review comments.

> ---
>  drivers/pci/host/pci-imx6.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
> index fdb9536..c63691c 100644
> --- a/drivers/pci/host/pci-imx6.c
> +++ b/drivers/pci/host/pci-imx6.c
> @@ -489,7 +489,7 @@ static int imx6_pcie_link_up(struct pcie_port *pp)
>  		 * Wait a little bit, then re-check if the link finished
>  		 * the training.
>  		 */
> -		usleep_range(1000, 2000);
> +		mdelay(20);
>  	}
>  	/*
>  	 * From L0, initiate MAC entry to gen2 if EP/RC supports gen2.
> -- 
> 1.8.4
>