Re: [PATCH v6 06/18] PCI: designware-ep: Add generic function for raising MSI irq

[Niklas Cassel]

On Thu, Dec 28, 2017 at 08:09:50PM +0530, Kishon Vijay Abraham I wrote:
> Hi Niklas,
> 
> On Thursday 28 December 2017 01:36 PM, Kishon Vijay Abraham I wrote:
> > Hi Niklas,
> > 
> > On Thursday 28 December 2017 03:59 AM, Niklas Cassel wrote:
> >> On Tue, Dec 26, 2017 at 06:20:54PM +0530, Kishon Vijay Abraham I wrote:
> >>> Hi Niklas,
> >>
> >> Hello Kishon
> >>
> >>>
> >>> On Wednesday 20 December 2017 04:59 AM, Niklas Cassel wrote:
> >>>> Add a generic function for raising MSI irqs that can be used by all
> >>>> DWC based controllers.
> >>>>
> >>>> Note that certain controllers, like DRA7xx, have a special convenience
> >>>> register for raising MSI irqs that doesn't require you to explicitly map
> >>>> the MSI address. Therefore, it is likely that certain drivers will
> >>>> not use this generic function, even if they can.
> >>>>
> >>>> Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxxx>
> >>>> ---
> >>>>  drivers/pci/dwc/pcie-designware-ep.c | 35 +++++++++++++++++++++++++++++++++++
> >>>>  drivers/pci/dwc/pcie-designware.h    |  9 +++++++++
> >>>>  2 files changed, 44 insertions(+)
> >>>>
> >>>> diff --git a/drivers/pci/dwc/pcie-designware-ep.c b/drivers/pci/dwc/pcie-designware-ep.c
> >>>> index 700ed2f4becf..c5aa1cac5041 100644
> >>>> --- a/drivers/pci/dwc/pcie-designware-ep.c
> >>>> +++ b/drivers/pci/dwc/pcie-designware-ep.c
> >>>> @@ -282,6 +282,41 @@ static const struct pci_epc_ops epc_ops = {
> >>>>  	.stop			= dw_pcie_ep_stop,
> >>>>  };
> >>>>  
> >>>> +int dw_pcie_ep_raise_msi_irq(struct dw_pcie_ep *ep,
> >>>> +			     u8 interrupt_num)
> >>>> +{
> >>>> +	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
> >>>> +	struct pci_epc *epc = ep->epc;
> >>>> +	u16 msg_ctrl, msg_data;
> >>>> +	u32 msg_addr_lower, msg_addr_upper;
> >>>> +	u64 msg_addr;
> >>>> +	bool has_upper;
> >>>> +	int ret;
> >>>> +
> >>>> +	/* Raise MSI per the PCI Local Bus Specification Revision 3.0, 6.8.1. */
> >>>> +	msg_ctrl = dw_pcie_readw_dbi(pci, MSI_MESSAGE_CONTROL);
> >>>> +	has_upper = !!(msg_ctrl & PCI_MSI_FLAGS_64BIT);
> >>>> +	msg_addr_lower = dw_pcie_readl_dbi(pci, MSI_MESSAGE_ADDR_L32);
> >>>> +	if (has_upper) {
> >>>> +		msg_addr_upper = dw_pcie_readl_dbi(pci, MSI_MESSAGE_ADDR_U32);
> >>>> +		msg_data = dw_pcie_readw_dbi(pci, MSI_MESSAGE_DATA_64);
> >>>> +	} else {
> >>>> +		msg_addr_upper = 0;
> >>>> +		msg_data = dw_pcie_readw_dbi(pci, MSI_MESSAGE_DATA_32);
> >>>> +	}
> >>>> +	msg_addr = ((u64) msg_addr_upper) << 32 | msg_addr_lower;
> >>>> +	ret = dw_pcie_ep_map_addr(epc, ep->msi_mem_phys, msg_addr,
> >>>> +				  epc->mem->page_size);
> >>>> +	if (ret)
> >>>> +		return ret;
> >>>> +
> >>>> +	writel(msg_data | (interrupt_num - 1), ep->msi_mem);
> >>>
> >>> Shouldn't this be msg_data + (interrupt_num - 1)?
> >>
> >> I'm not quite sure about this, but if there is a pending irq,
> >> not yet processed by the RC, the msg_data we read out in this
> >> function should have a bit set, matching the pending irq.
> > 
> > IIUC, the msg_data that we read here should not depend on the pending irq on
> > the RC side. msg_data should have the starting MSI vector number assigned by RC
> > for that EP device. (msg.data = pos; in dw_msi_setup_msg() also seem to suggest
> > the same).
> >>
> >> If that irq is the same as the irq we are trying to raise,
> >> doing an addition will produce a bogus vector number,
> >> but a bitwise or should work.
> > 
> > if msg_data has the starting MSI vector, doing an addition should get to the
> > correct MSI vector.
> >>
> >> For that reason, I think that doing bitwise or seems safer.
> >> However, other than this case, I don't see why it should
> >> matter if we do an addition or a bitwise or.
> >>
> >> Are you having some problem with the code?
> >> It seems to be working fine on ARTPEC-6:
> >>
> >> # ./pcitest -m 1
> >> MSI1:           OKAY
> >> # ./pcitest -m 2
> >> MSI2:           OKAY
> >> # ./pcitest -m 3
> >> MSI3:           OKAY
> >> # ./pcitest -m 4
> >> MSI4:           OKAY
> >> # ./pcitest -m 5
> >> MSI5:           OKAY
> >> # ./pcitest -m 6
> >> MSI6:           OKAY
> >> # ./pcitest -m 7
> >> MSI7:           OKAY
> >> # ./pcitest -m 8
> >> MSI8:           OKAY
> >> # ./pcitest -m 9
> >> MSI9:           OKAY
> >> # cat /proc/interrupts | grep -i msi
> >>  82:          9          0     GIC-0 180 Level     artpec6-pcie-msi
> >> 188:          1          0   PCI-MSI  16 Edge      pci-endpoint-test
> >> 189:          1          0   PCI-MSI  17 Edge      pci-endpoint-test
> >> 190:          1          0   PCI-MSI  18 Edge      pci-endpoint-test
> >> 191:          1          0   PCI-MSI  19 Edge      pci-endpoint-test
> >> 192:          1          0   PCI-MSI  20 Edge      pci-endpoint-test
> >> 193:          1          0   PCI-MSI  21 Edge      pci-endpoint-test
> >> 194:          1          0   PCI-MSI  22 Edge      pci-endpoint-test
> >> 195:          1          0   PCI-MSI  23 Edge      pci-endpoint-test
> >> 196:          1          0   PCI-MSI  24 Edge      pci-endpoint-test
> >> 197:          0          0   PCI-MSI  25 Edge      pci-endpoint-test
> >> 198:          0          0   PCI-MSI  26 Edge      pci-endpoint-test
> >> 199:          0          0   PCI-MSI  27 Edge      pci-endpoint-test
> >> 200:          0          0   PCI-MSI  28 Edge      pci-endpoint-test
> >> 201:          0          0   PCI-MSI  29 Edge      pci-endpoint-test
> >> 202:          0          0   PCI-MSI  30 Edge      pci-endpoint-test
> >> 203:          0          0   PCI-MSI  31 Edge      pci-endpoint-test
> >>
> >> From EP:
> >> irq: 1 read msg_data: 0x10 writing: 0x10
> >> irq: 2 read msg_data: 0x10 writing: 0x11
> >> irq: 3 read msg_data: 0x10 writing: 0x12
> >> irq: 4 read msg_data: 0x10 writing: 0x13
> >> irq: 5 read msg_data: 0x10 writing: 0x14
> >> irq: 6 read msg_data: 0x10 writing: 0x15
> >> irq: 7 read msg_data: 0x10 writing: 0x16
> >> irq: 8 read msg_data: 0x10 writing: 0x17
> >> irq: 9 read msg_data: 0x10 writing: 0x18
> > 
> > since your msg_data is 0x10, you are not facing the issue. What if it's 0x1? In
> > my case If I have Gustavo's patch series applied, msg_data has a value of 0x1
> > and I don't get certain MSI interrupts.
> 
> I think Gustavo's series doesn't align the MSI vector properly. That's why I
> get 0x1. So your patch is fine as such.

If the EP requests 16 irqs via Multiple Message Capable field,
and the host grants it 16 irqs, by writing "100" to Multiple Message
Enable field, then the endpoint can read MSI message data, modify
bits 0-3, then write this modified value to the MSI message address.

All bits that the EP is allowed to modify has to be initialized to
0 by the host. E.g., in order to be able to raise 16 unique irqs,
bits 0-3 has to be initialized to 0 (since we need to be able to use
the whole range, 0x0-0xf).

i.e. initializing MSI message data with 0x1 seems wrong, if the EP
is requesting 16 irqs.

Note that the case where Multiple Message Enable is "000", is special,
since then the EP is not allowed to modify any bit, so then it is ok
if bit 0 in MSI message data is set, but the code should handle this
case already.

So I agree, this patch should be fine as is.

Regards,
Niklas