[PATCH v4 4/4] PCI: cadence: Check link is up before sending IRQ from EP

[PATCH v4 4/4] PCI: cadence: Check link is up before sending IRQ from EP

[Alan Douglas]

If EP attempts to send an IRQ (legacy, MSI or MSI-X) while the
link is not up, return -EINVAL

Fixes: 37dddf14f1ae ("PCI: cadence: Add EndPoint Controller driver for Cadence PCIe controller")
Signed-off-by: Alan Douglas <adouglas@cadence.com>
---
 drivers/pci/controller/pcie-cadence-ep.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/pci/controller/pcie-cadence-ep.c b/drivers/pci/controller/pcie-cadence-ep.c
index b762214..3667d70 100644
--- a/drivers/pci/controller/pcie-cadence-ep.c
+++ b/drivers/pci/controller/pcie-cadence-ep.c
@@ -370,6 +370,12 @@ static int cdns_pcie_ep_raise_irq(struct pci_epc *epc, u8 fn,
 				  u16 interrupt_num)
 {
 	struct cdns_pcie_ep *ep = epc_get_drvdata(epc);
+	u32 link_status;
+
+	/* Can't send an IRQ if the link is down. */
+	link_status = cdns_pcie_readl(&ep->pcie, CDNS_PCIE_LM_BASE);
+	if (!(link_status & 0x1))
+		return -EINVAL;
 
 	switch (type) {
 	case PCI_EPC_IRQ_LEGACY:
-- 
1.9.0

Re: [PATCH v4 4/4] PCI: cadence: Check link is up before sending IRQ from EP

[Bjorn Helgaas]

On Thu, Oct 11, 2018 at 05:16:57PM +0100, Alan Douglas wrote:
> If EP attempts to send an IRQ (legacy, MSI or MSI-X) while the
> link is not up, return -EINVAL
> 
> Fixes: 37dddf14f1ae ("PCI: cadence: Add EndPoint Controller driver for Cadence PCIe controller")
> Signed-off-by: Alan Douglas <adouglas@cadence.com>
> ---
>  drivers/pci/controller/pcie-cadence-ep.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/pci/controller/pcie-cadence-ep.c b/drivers/pci/controller/pcie-cadence-ep.c
> index b762214..3667d70 100644
> --- a/drivers/pci/controller/pcie-cadence-ep.c
> +++ b/drivers/pci/controller/pcie-cadence-ep.c
> @@ -370,6 +370,12 @@ static int cdns_pcie_ep_raise_irq(struct pci_epc *epc, u8 fn,
>  				  u16 interrupt_num)
>  {
>  	struct cdns_pcie_ep *ep = epc_get_drvdata(epc);
> +	u32 link_status;
> +
> +	/* Can't send an IRQ if the link is down. */
> +	link_status = cdns_pcie_readl(&ep->pcie, CDNS_PCIE_LM_BASE);
> +	if (!(link_status & 0x1))
> +		return -EINVAL;

This looks racy.  What happens if the link goes down right after the
CDNS_PCIE_LM_BASE read, but before we get here?

>  	switch (type) {
>  	case PCI_EPC_IRQ_LEGACY:
> -- 
> 1.9.0
> 

Re: [PATCH v4 4/4] PCI: cadence: Check link is up before sending IRQ from EP

[Lorenzo Pieralisi]

On Mon, Oct 15, 2018 at 04:30:35PM -0500, Bjorn Helgaas wrote:
> On Thu, Oct 11, 2018 at 05:16:57PM +0100, Alan Douglas wrote:
> > If EP attempts to send an IRQ (legacy, MSI or MSI-X) while the
> > link is not up, return -EINVAL
> > 
> > Fixes: 37dddf14f1ae ("PCI: cadence: Add EndPoint Controller driver for Cadence PCIe controller")
> > Signed-off-by: Alan Douglas <adouglas@cadence.com>
> > ---
> >  drivers/pci/controller/pcie-cadence-ep.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/pcie-cadence-ep.c b/drivers/pci/controller/pcie-cadence-ep.c
> > index b762214..3667d70 100644
> > --- a/drivers/pci/controller/pcie-cadence-ep.c
> > +++ b/drivers/pci/controller/pcie-cadence-ep.c
> > @@ -370,6 +370,12 @@ static int cdns_pcie_ep_raise_irq(struct pci_epc *epc, u8 fn,
> >  				  u16 interrupt_num)
> >  {
> >  	struct cdns_pcie_ep *ep = epc_get_drvdata(epc);
> > +	u32 link_status;
> > +
> > +	/* Can't send an IRQ if the link is down. */
> > +	link_status = cdns_pcie_readl(&ep->pcie, CDNS_PCIE_LM_BASE);
> > +	if (!(link_status & 0x1))
> > +		return -EINVAL;
> 
> This looks racy.  What happens if the link goes down right after the
> CDNS_PCIE_LM_BASE read, but before we get here?

I agree with Bjorn, this check does not seem very useful and honestly
I think this patch should be dropped, I should not have queued it in
the first place.

I wonder whether something can actually be done in the EP subsystem
to handle this in a cleaner way.

Unless I hear a compelling reason to keep it in the patch queue I
would drop this patch.

Lorenzo

RE: [PATCH v4 4/4] PCI: cadence: Check link is up before sending IRQ from EP

[Alan Douglas]

Hi,

On 16 October 2018 14:53, Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote:
> On Mon, Oct 15, 2018 at 04:30:35PM -0500, Bjorn Helgaas wrote:
> > On Thu, Oct 11, 2018 at 05:16:57PM +0100, Alan Douglas wrote:
> > > If EP attempts to send an IRQ (legacy, MSI or MSI-X) while the
> > > link is not up, return -EINVAL
> > >
> > > Fixes: 37dddf14f1ae ("PCI: cadence: Add EndPoint Controller driver for Cadence PCIe controller")
> > > Signed-off-by: Alan Douglas <adouglas@cadence.com>
> > > ---
> > >  drivers/pci/controller/pcie-cadence-ep.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/drivers/pci/controller/pcie-cadence-ep.c b/drivers/pci/controller/pcie-cadence-ep.c
> > > index b762214..3667d70 100644
> > > --- a/drivers/pci/controller/pcie-cadence-ep.c
> > > +++ b/drivers/pci/controller/pcie-cadence-ep.c
> > > @@ -370,6 +370,12 @@ static int cdns_pcie_ep_raise_irq(struct pci_epc *epc, u8 fn,
> > >  				  u16 interrupt_num)
> > >  {
> > >  	struct cdns_pcie_ep *ep = epc_get_drvdata(epc);
> > > +	u32 link_status;
> > > +
> > > +	/* Can't send an IRQ if the link is down. */
> > > +	link_status = cdns_pcie_readl(&ep->pcie, CDNS_PCIE_LM_BASE);
> > > +	if (!(link_status & 0x1))
> > > +		return -EINVAL;
> >
> > This looks racy.  What happens if the link goes down right after the
> > CDNS_PCIE_LM_BASE read, but before we get here?
> 
> I agree with Bjorn, this check does not seem very useful and honestly
> I think this patch should be dropped, I should not have queued it in
> the first place.
> 
> I wonder whether something can actually be done in the EP subsystem
> to handle this in a cleaner way.
> 
> Unless I hear a compelling reason to keep it in the patch queue I
> would drop this patch.
> 
> Lorenzo
Makes sense to me, I was just preparing a reply.  I need to find
a fix that will work for all cases, possibly using the handshake
for the D0->D3 Config write which should precede the link down. At
the moment I think we need to insist that the link is always up while
the EP driver is loaded.

Alan