| Message ID | 20200528143141.29956-1-pali@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | PCI: aardvark: Don't touch PCIe registers if no card connected | expand |
On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > When there is no PCIe card connected and advk_pcie_rd_conf() or > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > root bridge, the aardvark driver throws the following error message: > > advk-pcie d0070000.pcie: config read/write timed out > > Obviously accessing PCIe registers of disconnected card is not possible. > > Extend check in advk_pcie_valid_device() function for validating > availability of PCIe bus. If PCIe link is down, then the device is marked > as Not Found and the driver does not try to access these registers. > > Signed-off-by: Pali Rohár <pali@kernel.org> > --- > drivers/pci/controller/pci-aardvark.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > index 90ff291c24f0..53a4cfd7d377 100644 > --- a/drivers/pci/controller/pci-aardvark.c > +++ b/drivers/pci/controller/pci-aardvark.c > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > return false; > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > + return false; I don't think this is the right fix. This makes it racy because the link may go down after we call advk_pcie_valid_device() but before we perform the config read. I have no objection to removing the "config read/write timed out" message. The "return PCIBIOS_SET_FAILED" in the read case probably should be augmented by setting "*val = 0xffffffff". > return true; > } > > -- > 2.20.1 >
On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote: > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > > When there is no PCIe card connected and advk_pcie_rd_conf() or > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > > root bridge, the aardvark driver throws the following error message: > > > > advk-pcie d0070000.pcie: config read/write timed out > > > > Obviously accessing PCIe registers of disconnected card is not possible. > > > > Extend check in advk_pcie_valid_device() function for validating > > availability of PCIe bus. If PCIe link is down, then the device is marked > > as Not Found and the driver does not try to access these registers. > > > > Signed-off-by: Pali Rohár <pali@kernel.org> > > --- > > drivers/pci/controller/pci-aardvark.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > index 90ff291c24f0..53a4cfd7d377 100644 > > --- a/drivers/pci/controller/pci-aardvark.c > > +++ b/drivers/pci/controller/pci-aardvark.c > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > > return false; > > > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > > + return false; > > I don't think this is the right fix. This makes it racy because the > link may go down after we call advk_pcie_valid_device() but before we > perform the config read. Yes, it is racy, but I do not think it cause problems. Trying to read PCIe registers when device is not connected cause just those timeouts, printing error message and increased delay in advk_pcie_wait_pio() due to polling loop. This patch reduce unnecessary access to PCIe registers when advk_pcie_wait_pio() polling just fail. I think it is a good idea to not call blocking advk_pcie_wait_pio() when it is not needed. We could have faster enumeration of PCIe buses when card is not connected. > I have no objection to removing the "config read/write timed out" > message. The "return PCIBIOS_SET_FAILED" in the read case probably > should be augmented by setting "*val = 0xffffffff". > > > return true; > > } > > > > -- > > 2.20.1 > >
On Thu, May 28, 2020 at 06:38:09PM +0200, Pali Rohár wrote: > On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote: > > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > > > When there is no PCIe card connected and advk_pcie_rd_conf() or > > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > > > root bridge, the aardvark driver throws the following error message: > > > > > > advk-pcie d0070000.pcie: config read/write timed out > > > > > > Obviously accessing PCIe registers of disconnected card is not possible. > > > > > > Extend check in advk_pcie_valid_device() function for validating > > > availability of PCIe bus. If PCIe link is down, then the device is marked > > > as Not Found and the driver does not try to access these registers. > > > > > > Signed-off-by: Pali Rohár <pali@kernel.org> > > > --- > > > drivers/pci/controller/pci-aardvark.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > index 90ff291c24f0..53a4cfd7d377 100644 > > > --- a/drivers/pci/controller/pci-aardvark.c > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > > > return false; > > > > > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > > > + return false; > > > > I don't think this is the right fix. This makes it racy because the > > link may go down after we call advk_pcie_valid_device() but before we > > perform the config read. > > Yes, it is racy, but I do not think it cause problems. Trying to read > PCIe registers when device is not connected cause just those timeouts, > printing error message and increased delay in advk_pcie_wait_pio() due > to polling loop. This patch reduce unnecessary access to PCIe registers > when advk_pcie_wait_pio() polling just fail. > > I think it is a good idea to not call blocking advk_pcie_wait_pio() when > it is not needed. We could have faster enumeration of PCIe buses when > card is not connected. Maybe advk_pcie_check_pio_status() and advk_pcie_wait_pio() could be combined so we could get the correct error status as soon as it's available, without waiting for a timeout? In any event, the "return PCIBIOS_SET_FAILED" needs to be fixed. Most callers of config read do not check for failure, but most of the ones that do, check for "val == ~0". Only a few check for a status of other than PCIBIOS_SUCCESSFUL. > > I have no objection to removing the "config read/write timed out" > > message. The "return PCIBIOS_SET_FAILED" in the read case probably > > should be augmented by setting "*val = 0xffffffff". > > > > > return true; > > > } > > > > > > -- > > > 2.20.1 > > >
On Thursday 28 May 2020 11:49:38 Bjorn Helgaas wrote: > On Thu, May 28, 2020 at 06:38:09PM +0200, Pali Rohár wrote: > > On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote: > > > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > > > > When there is no PCIe card connected and advk_pcie_rd_conf() or > > > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > > > > root bridge, the aardvark driver throws the following error message: > > > > > > > > advk-pcie d0070000.pcie: config read/write timed out > > > > > > > > Obviously accessing PCIe registers of disconnected card is not possible. > > > > > > > > Extend check in advk_pcie_valid_device() function for validating > > > > availability of PCIe bus. If PCIe link is down, then the device is marked > > > > as Not Found and the driver does not try to access these registers. > > > > > > > > Signed-off-by: Pali Rohár <pali@kernel.org> > > > > --- > > > > drivers/pci/controller/pci-aardvark.c | 3 +++ > > > > 1 file changed, 3 insertions(+) > > > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > > index 90ff291c24f0..53a4cfd7d377 100644 > > > > --- a/drivers/pci/controller/pci-aardvark.c > > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > > > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > > > > return false; > > > > > > > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > > > > + return false; > > > > > > I don't think this is the right fix. This makes it racy because the > > > link may go down after we call advk_pcie_valid_device() but before we > > > perform the config read. > > > > Yes, it is racy, but I do not think it cause problems. Trying to read > > PCIe registers when device is not connected cause just those timeouts, > > printing error message and increased delay in advk_pcie_wait_pio() due > > to polling loop. This patch reduce unnecessary access to PCIe registers > > when advk_pcie_wait_pio() polling just fail. > > > > I think it is a good idea to not call blocking advk_pcie_wait_pio() when > > it is not needed. We could have faster enumeration of PCIe buses when > > card is not connected. > > Maybe advk_pcie_check_pio_status() and advk_pcie_wait_pio() could be > combined so we could get the correct error status as soon as it's > available, without waiting for a timeout? Any idea how to achieve it? First call is polling function advk_pcie_wait_pio() and second call is advk_pcie_check_pio_status() which just reads status register and prints error message to dmesg. So for me it looks like that combining these two functions into one does not change anything. We always need to call polling code prior to checking status register. And therefore need to wait for timeout. Unless something like in this proposed patch is not used (to skip whole register access if it would fail). > In any event, the "return PCIBIOS_SET_FAILED" needs to be fixed. Most > callers of config read do not check for failure, but most of the ones > that do, check for "val == ~0". Only a few check for a status of > other than PCIBIOS_SUCCESSFUL. > > > > I have no objection to removing the "config read/write timed out" > > > message. The "return PCIBIOS_SET_FAILED" in the read case probably > > > should be augmented by setting "*val = 0xffffffff". Now I see, "*val = 0xffffffff" should be really set when function advk_pcie_rd_conf() fails. > > > > return true; > > > > } > > > > > > > > -- > > > > 2.20.1 > > > >
Hello! On Friday 29 May 2020 10:30:13 Pali Rohár wrote: > On Thursday 28 May 2020 11:49:38 Bjorn Helgaas wrote: > > On Thu, May 28, 2020 at 06:38:09PM +0200, Pali Rohár wrote: > > > On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote: > > > > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > > > > > When there is no PCIe card connected and advk_pcie_rd_conf() or > > > > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > > > > > root bridge, the aardvark driver throws the following error message: > > > > > > > > > > advk-pcie d0070000.pcie: config read/write timed out > > > > > > > > > > Obviously accessing PCIe registers of disconnected card is not possible. > > > > > > > > > > Extend check in advk_pcie_valid_device() function for validating > > > > > availability of PCIe bus. If PCIe link is down, then the device is marked > > > > > as Not Found and the driver does not try to access these registers. > > > > > > > > > > Signed-off-by: Pali Rohár <pali@kernel.org> > > > > > --- > > > > > drivers/pci/controller/pci-aardvark.c | 3 +++ > > > > > 1 file changed, 3 insertions(+) > > > > > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > > > index 90ff291c24f0..53a4cfd7d377 100644 > > > > > --- a/drivers/pci/controller/pci-aardvark.c > > > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > > > > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > > > > > return false; > > > > > > > > > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > > > > > + return false; > > > > > > > > I don't think this is the right fix. This makes it racy because the > > > > link may go down after we call advk_pcie_valid_device() but before we > > > > perform the config read. > > > > > > Yes, it is racy, but I do not think it cause problems. Trying to read > > > PCIe registers when device is not connected cause just those timeouts, > > > printing error message and increased delay in advk_pcie_wait_pio() due > > > to polling loop. This patch reduce unnecessary access to PCIe registers > > > when advk_pcie_wait_pio() polling just fail. > > > > > > I think it is a good idea to not call blocking advk_pcie_wait_pio() when > > > it is not needed. We could have faster enumeration of PCIe buses when > > > card is not connected. > > > > Maybe advk_pcie_check_pio_status() and advk_pcie_wait_pio() could be > > combined so we could get the correct error status as soon as it's > > available, without waiting for a timeout? > > Any idea how to achieve it? > > First call is polling function advk_pcie_wait_pio() and second call is > advk_pcie_check_pio_status() which just reads status register and prints > error message to dmesg. > > So for me it looks like that combining these two functions into one does > not change anything. We always need to call polling code prior to > checking status register. And therefore need to wait for timeout. Unless > something like in this proposed patch is not used (to skip whole > register access if it would fail). So to answer your question, correct status is possible to retrieve only after waiting for timeout. As status would be available only after timeout expires. Therefore my proposed patch in this (or some other) form is needed if we want to prevent trying to read from registers and waiting for answer when card is disconnected. I would really like to see this issue fixed, so booting linux kernel on board without connected PCIe card would not be delayed. Thomas, Lorenzo, Bjorn: do you have any idea how to fix it differently? Or if not, could be my proposed patch accepted in some form? > > In any event, the "return PCIBIOS_SET_FAILED" needs to be fixed. Most > > callers of config read do not check for failure, but most of the ones > > that do, check for "val == ~0". Only a few check for a status of > > other than PCIBIOS_SUCCESSFUL. > > > > > > I have no objection to removing the "config read/write timed out" > > > > message. The "return PCIBIOS_SET_FAILED" in the read case probably > > > > should be augmented by setting "*val = 0xffffffff". > > Now I see, "*val = 0xffffffff" should be really set when function > advk_pcie_rd_conf() fails. I have already sent separate patch which fixes this issue. > > > > > return true; > > > > > } > > > > > > > > > > -- > > > > > 2.20.1 > > > > >
On Thu, May 28, 2020 at 06:38:09PM +0200, Pali Rohár wrote: > On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote: > > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > > > When there is no PCIe card connected and advk_pcie_rd_conf() or > > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > > > root bridge, the aardvark driver throws the following error message: > > > > > > advk-pcie d0070000.pcie: config read/write timed out > > > > > > Obviously accessing PCIe registers of disconnected card is not possible. > > > > > > Extend check in advk_pcie_valid_device() function for validating > > > availability of PCIe bus. If PCIe link is down, then the device is marked > > > as Not Found and the driver does not try to access these registers. > > > > > > Signed-off-by: Pali Rohár <pali@kernel.org> > > > --- > > > drivers/pci/controller/pci-aardvark.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > index 90ff291c24f0..53a4cfd7d377 100644 > > > --- a/drivers/pci/controller/pci-aardvark.c > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > > > return false; > > > > > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > > > + return false; > > > > I don't think this is the right fix. This makes it racy because the > > link may go down after we call advk_pcie_valid_device() but before we > > perform the config read. > > Yes, it is racy, but I do not think it cause problems. Trying to read > PCIe registers when device is not connected cause just those timeouts, > printing error message and increased delay in advk_pcie_wait_pio() due > to polling loop. This patch reduce unnecessary access to PCIe registers > when advk_pcie_wait_pio() polling just fail. What happens when the device is removed after advk_pcie_link_up() returns true, but before we actually do the config access?
On Tuesday 30 June 2020 08:51:27 Bjorn Helgaas wrote: > On Thu, May 28, 2020 at 06:38:09PM +0200, Pali Rohár wrote: > > On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote: > > > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > > > > When there is no PCIe card connected and advk_pcie_rd_conf() or > > > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > > > > root bridge, the aardvark driver throws the following error message: > > > > > > > > advk-pcie d0070000.pcie: config read/write timed out > > > > > > > > Obviously accessing PCIe registers of disconnected card is not possible. > > > > > > > > Extend check in advk_pcie_valid_device() function for validating > > > > availability of PCIe bus. If PCIe link is down, then the device is marked > > > > as Not Found and the driver does not try to access these registers. > > > > > > > > Signed-off-by: Pali Rohár <pali@kernel.org> > > > > --- > > > > drivers/pci/controller/pci-aardvark.c | 3 +++ > > > > 1 file changed, 3 insertions(+) > > > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > > index 90ff291c24f0..53a4cfd7d377 100644 > > > > --- a/drivers/pci/controller/pci-aardvark.c > > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > > > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > > > > return false; > > > > > > > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > > > > + return false; > > > > > > I don't think this is the right fix. This makes it racy because the > > > link may go down after we call advk_pcie_valid_device() but before we > > > perform the config read. > > > > Yes, it is racy, but I do not think it cause problems. Trying to read > > PCIe registers when device is not connected cause just those timeouts, > > printing error message and increased delay in advk_pcie_wait_pio() due > > to polling loop. This patch reduce unnecessary access to PCIe registers > > when advk_pcie_wait_pio() polling just fail. > > What happens when the device is removed after advk_pcie_link_up() > returns true, but before we actually do the config access? Do you mean to remove device physically at runtime? I was told that our board would crash or issue reset. Removing device from mini PCIe slot without power off is not supported. Anyway, currently we are trying to read from device registers even when no device is connected. So when advk_pcie_link_up() returns true and after that device is not connected (somehow board and kernel would be still alive) I guess that it would behave as without applying this patch. So kernel starts reading from register and would wait until timeout expires. As device is not connected there would be no answer, so kernel print error message to dmesg (same as in commit message) and returns error that read failed.
On Tue, Jun 30, 2020 at 04:04:20PM +0200, Pali Rohár wrote: > On Tuesday 30 June 2020 08:51:27 Bjorn Helgaas wrote: > > On Thu, May 28, 2020 at 06:38:09PM +0200, Pali Rohár wrote: > > > On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote: > > > > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > > > > > When there is no PCIe card connected and advk_pcie_rd_conf() or > > > > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > > > > > root bridge, the aardvark driver throws the following error message: > > > > > > > > > > advk-pcie d0070000.pcie: config read/write timed out > > > > > > > > > > Obviously accessing PCIe registers of disconnected card is not possible. > > > > > > > > > > Extend check in advk_pcie_valid_device() function for validating > > > > > availability of PCIe bus. If PCIe link is down, then the device is marked > > > > > as Not Found and the driver does not try to access these registers. > > > > > > > > > > Signed-off-by: Pali Rohár <pali@kernel.org> > > > > > --- > > > > > drivers/pci/controller/pci-aardvark.c | 3 +++ > > > > > 1 file changed, 3 insertions(+) > > > > > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > > > index 90ff291c24f0..53a4cfd7d377 100644 > > > > > --- a/drivers/pci/controller/pci-aardvark.c > > > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > > > > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > > > > > return false; > > > > > > > > > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > > > > > + return false; > > > > > > > > I don't think this is the right fix. This makes it racy because the > > > > link may go down after we call advk_pcie_valid_device() but before we > > > > perform the config read. > > > > > > Yes, it is racy, but I do not think it cause problems. Trying to read > > > PCIe registers when device is not connected cause just those timeouts, > > > printing error message and increased delay in advk_pcie_wait_pio() due > > > to polling loop. This patch reduce unnecessary access to PCIe registers > > > when advk_pcie_wait_pio() polling just fail. > > > > What happens when the device is removed after advk_pcie_link_up() > > returns true, but before we actually do the config access? > > Do you mean to remove device physically at runtime? I was told that our > board would crash or issue reset. Removing device from mini PCIe slot > without power off is not supported. Right, I don't think PCIe mini cards support hotplug. > Anyway, currently we are trying to read from device registers even when > no device is connected. So when advk_pcie_link_up() returns true and > after that device is not connected (somehow board and kernel would be > still alive) I guess that it would behave as without applying this > patch. So kernel starts reading from register and would wait until > timeout expires. As device is not connected there would be no answer, > so kernel print error message to dmesg (same as in commit message) and > returns error that read failed. OK, so if I understand correctly, checking advk_pcie_link_up() is strictly an optimization. If we guess wrong (e.g., after calling advk_pcie_link_up(), the link went down because the card was removed, DPC triggered, etc), the only bad thing is that we wait for a timeout; it never causes a crash. If that's the case, I'm fine with this. But please add a comment to that effect. I think several other drivers check for the link being up because we actually crash if we try to read config space when the link is down. That's what I was trying to avoid here. Bjorn
On Tuesday 30 June 2020 09:58:48 Bjorn Helgaas wrote: > On Tue, Jun 30, 2020 at 04:04:20PM +0200, Pali Rohár wrote: > > On Tuesday 30 June 2020 08:51:27 Bjorn Helgaas wrote: > > > On Thu, May 28, 2020 at 06:38:09PM +0200, Pali Rohár wrote: > > > > On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote: > > > > > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > > > > > > When there is no PCIe card connected and advk_pcie_rd_conf() or > > > > > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > > > > > > root bridge, the aardvark driver throws the following error message: > > > > > > > > > > > > advk-pcie d0070000.pcie: config read/write timed out > > > > > > > > > > > > Obviously accessing PCIe registers of disconnected card is not possible. > > > > > > > > > > > > Extend check in advk_pcie_valid_device() function for validating > > > > > > availability of PCIe bus. If PCIe link is down, then the device is marked > > > > > > as Not Found and the driver does not try to access these registers. > > > > > > > > > > > > Signed-off-by: Pali Rohár <pali@kernel.org> > > > > > > --- > > > > > > drivers/pci/controller/pci-aardvark.c | 3 +++ > > > > > > 1 file changed, 3 insertions(+) > > > > > > > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > > > > index 90ff291c24f0..53a4cfd7d377 100644 > > > > > > --- a/drivers/pci/controller/pci-aardvark.c > > > > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > > > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > > > > > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > > > > > > return false; > > > > > > > > > > > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > > > > > > + return false; > > > > > > > > > > I don't think this is the right fix. This makes it racy because the > > > > > link may go down after we call advk_pcie_valid_device() but before we > > > > > perform the config read. > > > > > > > > Yes, it is racy, but I do not think it cause problems. Trying to read > > > > PCIe registers when device is not connected cause just those timeouts, > > > > printing error message and increased delay in advk_pcie_wait_pio() due > > > > to polling loop. This patch reduce unnecessary access to PCIe registers > > > > when advk_pcie_wait_pio() polling just fail. > > > > > > What happens when the device is removed after advk_pcie_link_up() > > > returns true, but before we actually do the config access? > > > > Do you mean to remove device physically at runtime? I was told that our > > board would crash or issue reset. Removing device from mini PCIe slot > > without power off is not supported. > > Right, I don't think PCIe mini cards support hotplug. > > > Anyway, currently we are trying to read from device registers even when > > no device is connected. So when advk_pcie_link_up() returns true and > > after that device is not connected (somehow board and kernel would be > > still alive) I guess that it would behave as without applying this > > patch. So kernel starts reading from register and would wait until > > timeout expires. As device is not connected there would be no answer, > > so kernel print error message to dmesg (same as in commit message) and > > returns error that read failed. > > OK, so if I understand correctly, checking advk_pcie_link_up() is > strictly an optimization. If we guess wrong (e.g., after calling > advk_pcie_link_up(), the link went down because the card was removed, > DPC triggered, etc), the only bad thing is that we wait for a timeout; > it never causes a crash. Yes. > If that's the case, I'm fine with this. But please add a comment to > that effect. Ok, I will send V2 with updated commit message. > I think several other drivers check for the link being up because we > actually crash if we try to read config space when the link is down. > That's what I was trying to avoid here. > > Bjorn
diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c index 90ff291c24f0..53a4cfd7d377 100644 --- a/drivers/pci/controller/pci-aardvark.c +++ b/drivers/pci/controller/pci-aardvark.c @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) return false; + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) + return false; + return true; }
When there is no PCIe card connected and advk_pcie_rd_conf() or advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated root bridge, the aardvark driver throws the following error message: advk-pcie d0070000.pcie: config read/write timed out Obviously accessing PCIe registers of disconnected card is not possible. Extend check in advk_pcie_valid_device() function for validating availability of PCIe bus. If PCIe link is down, then the device is marked as Not Found and the driver does not try to access these registers. Signed-off-by: Pali Rohár <pali@kernel.org> --- drivers/pci/controller/pci-aardvark.c | 3 +++ 1 file changed, 3 insertions(+)