[PATCH] PCI: Increase VPD access timeout

[PATCH] PCI: Increase VPD access timeout

[Matthew R. Ochs]

The PCI core uses a fixed 50ms timeout when waiting for VPD accesses to
complete. When an access does not complete within this period, a warning
is logged and an error returned to the caller.

While this default timeout is valid for most hardware, some devices can
experience longer access delays under certain circumstances. For example,
one of the IBM CXL Flash devices can take up to ~120ms in a worst-case
scenario. These types of devices can benefit from an extended timeout.

To support devices with a longer access delay, increase the timeout in
pci_vpd_wait() to 125ms. The PCI specification is silent with respect to
VPD delays, therefore there is no concern for violating a threshold.

Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
---
 drivers/pci/access.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index d11cdbb..61b5a6b 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -355,7 +355,7 @@ static size_t pci_vpd_size(struct pci_dev *dev, size_t old_size)
 static int pci_vpd_wait(struct pci_dev *dev)
 {
 	struct pci_vpd *vpd = dev->vpd;
-	unsigned long timeout = jiffies + msecs_to_jiffies(50);
+	unsigned long timeout = jiffies + msecs_to_jiffies(125);
 	unsigned long max_sleep = 16;
 	u16 status;
 	int ret;
-- 
2.1.0

Re: [PATCH] PCI: Increase VPD access timeout

[Gavin Shan]

On Tue, Nov 29, 2016 at 12:00:40PM -0600, Matthew R. Ochs wrote:
>The PCI core uses a fixed 50ms timeout when waiting for VPD accesses to
>complete. When an access does not complete within this period, a warning
>is logged and an error returned to the caller.
>
>While this default timeout is valid for most hardware, some devices can
>experience longer access delays under certain circumstances. For example,
>one of the IBM CXL Flash devices can take up to ~120ms in a worst-case
>scenario. These types of devices can benefit from an extended timeout.
>
>To support devices with a longer access delay, increase the timeout in
>pci_vpd_wait() to 125ms. The PCI specification is silent with respect to
>VPD delays, therefore there is no concern for violating a threshold.
>
>Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>

Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>

>---
> drivers/pci/access.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/drivers/pci/access.c b/drivers/pci/access.c
>index d11cdbb..61b5a6b 100644
>--- a/drivers/pci/access.c
>+++ b/drivers/pci/access.c
>@@ -355,7 +355,7 @@ static size_t pci_vpd_size(struct pci_dev *dev, size_t old_size)
> static int pci_vpd_wait(struct pci_dev *dev)
> {
> 	struct pci_vpd *vpd = dev->vpd;
>-	unsigned long timeout = jiffies + msecs_to_jiffies(50);
>+	unsigned long timeout = jiffies + msecs_to_jiffies(125);
> 	unsigned long max_sleep = 16;
> 	u16 status;
> 	int ret;
>-- 
>2.1.0
>
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>

Re: [PATCH] PCI: Increase VPD access timeout

[Uma Krishnan]

> The PCI core uses a fixed 50ms timeout when waiting for VPD accesses to
> complete. When an access does not complete within this period, a warning
> is logged and an error returned to the caller.
>
> While this default timeout is valid for most hardware, some devices can
> experience longer access delays under certain circumstances. For example,
> one of the IBM CXL Flash devices can take up to ~120ms in a worst-case
> scenario. These types of devices can benefit from an extended timeout.
>
> To support devices with a longer access delay, increase the timeout in
> pci_vpd_wait() to 125ms. The PCI specification is silent with respect to
> VPD delays, therefore there is no concern for violating a threshold.
>
> Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>

Tested-by: Uma Krishnan <ukrishn@linux.vnet.ibm.com>

Re: [PATCH] PCI: Increase VPD access timeout

[Matthew R. Ochs]

> On Nov 29, 2016, at 12:00 PM, Matthew R. Ochs <mrochs@linux.vnet.ibm.com> wrote:
> 
> The PCI core uses a fixed 50ms timeout when waiting for VPD accesses to
> complete. When an access does not complete within this period, a warning
> is logged and an error returned to the caller.
> 
> While this default timeout is valid for most hardware, some devices can
> experience longer access delays under certain circumstances. For example,
> one of the IBM CXL Flash devices can take up to ~120ms in a worst-case
> scenario. These types of devices can benefit from an extended timeout.
> 
> To support devices with a longer access delay, increase the timeout in
> pci_vpd_wait() to 125ms. The PCI specification is silent with respect to
> VPD delays, therefore there is no concern for violating a threshold.

Hi Bjorn,

It's been about a month since I originally sent this, and I wanted to know
if you've had a chance to look it over. Would like to get this queued up for
4.11 if possible.


-matt

> 
> Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
> ---
> drivers/pci/access.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index d11cdbb..61b5a6b 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -355,7 +355,7 @@ static size_t pci_vpd_size(struct pci_dev *dev, size_t old_size)
> static int pci_vpd_wait(struct pci_dev *dev)
> {
> 	struct pci_vpd *vpd = dev->vpd;
> -	unsigned long timeout = jiffies + msecs_to_jiffies(50);
> +	unsigned long timeout = jiffies + msecs_to_jiffies(125);
> 	unsigned long max_sleep = 16;
> 	u16 status;
> 	int ret;
> -- 
> 2.1.0
> 
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Re: [PATCH] PCI: Increase VPD access timeout

[Bjorn Helgaas]

On Tue, Nov 29, 2016 at 12:00:40PM -0600, Matthew R. Ochs wrote:
> The PCI core uses a fixed 50ms timeout when waiting for VPD accesses to
> complete. When an access does not complete within this period, a warning
> is logged and an error returned to the caller.
> 
> While this default timeout is valid for most hardware, some devices can
> experience longer access delays under certain circumstances. For example,
> one of the IBM CXL Flash devices can take up to ~120ms in a worst-case
> scenario. These types of devices can benefit from an extended timeout.
> 
> To support devices with a longer access delay, increase the timeout in
> pci_vpd_wait() to 125ms. The PCI specification is silent with respect to
> VPD delays, therefore there is no concern for violating a threshold.
> 
> Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>

Applied to pci/vpd for v4.11, with Tested-by Uma and Reviewed-by Gavin,
thanks!

> ---
>  drivers/pci/access.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index d11cdbb..61b5a6b 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -355,7 +355,7 @@ static size_t pci_vpd_size(struct pci_dev *dev, size_t old_size)
>  static int pci_vpd_wait(struct pci_dev *dev)
>  {
>  	struct pci_vpd *vpd = dev->vpd;
> -	unsigned long timeout = jiffies + msecs_to_jiffies(50);
> +	unsigned long timeout = jiffies + msecs_to_jiffies(125);
>  	unsigned long max_sleep = 16;
>  	u16 status;
>  	int ret;
> -- 
> 2.1.0
> 
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