| Message ID | 20190927083142.8571-1-repk@triplefau.lt |
|---|---|
| State | Superseded |
| Delegated to: | Lorenzo Pieralisi |
| Headers | show |
| Series | [v2] PCI: aardvark: Don't rely on jiffies while holding spinlock | expand |
Hello Remi, Thanks for the new iteration! On Fri, 27 Sep 2019 10:31:42 +0200 Remi Pommarel <repk@triplefau.lt> wrote: > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > index fc0fe4d4de49..ee05ccb2b686 100644 > --- a/drivers/pci/controller/pci-aardvark.c > +++ b/drivers/pci/controller/pci-aardvark.c > @@ -175,7 +175,8 @@ > (PCIE_CONF_BUS(bus) | PCIE_CONF_DEV(PCI_SLOT(devfn)) | \ > PCIE_CONF_FUNC(PCI_FUNC(devfn)) | PCIE_CONF_REG(where)) > > -#define PIO_TIMEOUT_MS 1 > +#define PIO_RETRY_CNT 10 > +#define PIO_RETRY_DELAY 2 /* 2 us*/ So this changes the timeout from 1ms to just 20us, a division by 50 from the previous timeout value. From my measurements, it could sometime take up to 6us from a single PIO read operation to complete, which is getting close to the 20us timeout. Shouldn't PIO_RETRY_CNT be kept at 500, so that we keep using a 1ms timeout ? Thomas
Hi Thomas, On Fri, Sep 27, 2019 at 10:34:20AM +0200, Thomas Petazzoni wrote: > Hello Remi, > > Thanks for the new iteration! > > On Fri, 27 Sep 2019 10:31:42 +0200 > Remi Pommarel <repk@triplefau.lt> wrote: > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > index fc0fe4d4de49..ee05ccb2b686 100644 > > --- a/drivers/pci/controller/pci-aardvark.c > > +++ b/drivers/pci/controller/pci-aardvark.c > > @@ -175,7 +175,8 @@ > > (PCIE_CONF_BUS(bus) | PCIE_CONF_DEV(PCI_SLOT(devfn)) | \ > > PCIE_CONF_FUNC(PCI_FUNC(devfn)) | PCIE_CONF_REG(where)) > > > > -#define PIO_TIMEOUT_MS 1 > > +#define PIO_RETRY_CNT 10 > > +#define PIO_RETRY_DELAY 2 /* 2 us*/ > > So this changes the timeout from 1ms to just 20us, a division by 50 > from the previous timeout value. From my measurements, it could > sometime take up to 6us from a single PIO read operation to complete, > which is getting close to the 20us timeout. > > Shouldn't PIO_RETRY_CNT be kept at 500, so that we keep using a 1ms > timeout ? Damn. You right of course, sorry about that. Thanks
diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c index fc0fe4d4de49..ee05ccb2b686 100644 --- a/drivers/pci/controller/pci-aardvark.c +++ b/drivers/pci/controller/pci-aardvark.c @@ -175,7 +175,8 @@ (PCIE_CONF_BUS(bus) | PCIE_CONF_DEV(PCI_SLOT(devfn)) | \ PCIE_CONF_FUNC(PCI_FUNC(devfn)) | PCIE_CONF_REG(where)) -#define PIO_TIMEOUT_MS 1 +#define PIO_RETRY_CNT 10 +#define PIO_RETRY_DELAY 2 /* 2 us*/ #define LINK_WAIT_MAX_RETRIES 10 #define LINK_WAIT_USLEEP_MIN 90000 @@ -383,17 +384,16 @@ static void advk_pcie_check_pio_status(struct advk_pcie *pcie) static int advk_pcie_wait_pio(struct advk_pcie *pcie) { struct device *dev = &pcie->pdev->dev; - unsigned long timeout; + int i; - timeout = jiffies + msecs_to_jiffies(PIO_TIMEOUT_MS); - - while (time_before(jiffies, timeout)) { + for (i = 0; i < PIO_RETRY_CNT; i++) { u32 start, isr; start = advk_readl(pcie, PIO_START); isr = advk_readl(pcie, PIO_ISR); if (!start && isr) return 0; + udelay(PIO_RETRY_DELAY); } dev_err(dev, "config read/write timed out\n");
advk_pcie_wait_pio() can be called while holding a spinlock (from pci_bus_read_config_dword()), then depends on jiffies in order to timeout while polling on PIO state registers. In the case the PIO transaction failed, the timeout will never happen and will also cause the cpu to stall. This decrements a variable and wait instead of using jiffies. Signed-off-by: Remi Pommarel <repk@triplefau.lt> --- Changes since v1: - Reduce polling delay - Change size_t into int for loop counter --- drivers/pci/controller/pci-aardvark.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)