linux-kernel - Re: [PATCH v2 1/2] PCI: dra7xx: Fix legacy INTD IRQ handling

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Date:   Mon, 8 Jan 2018 18:24:45 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Vignesh R <vigneshr@...com>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-omap@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] PCI: dra7xx: Fix legacy INTD IRQ handling

On Mon, Jan 08, 2018 at 07:18:59PM +0530, Vignesh R wrote:
> 
> 
> On Thursday 04 January 2018 09:42 PM, Lorenzo Pieralisi wrote:
> > On Thu, Jan 04, 2018 at 07:04:30PM +0530, Kishon Vijay Abraham I wrote:
> >> Hi,
> >>
> >> On Thursday 04 January 2018 11:38 AM, Kishon Vijay Abraham I wrote:
> >>>
> >>>
> >>> On Friday 29 December 2017 05:11 PM, Vignesh R wrote:
> >>>> Legacy INTD IRQ handling is broken on dra7xx due to fact that driver
> >>>> uses hwirq in range of 1-4 for INTA, INTD whereas IRQ domain is of size
> >>>> 4 which is numbered 0-3. Therefore when INTD IRQ line is used with
> >>>> pci-dra7xx driver following warning is seen:
> >>>>
> >>>>        WARNING: CPU: 0 PID: 1 at kernel/irq/irqdomain.c:342 irq_domain_associate+0x12c/0x1c4
> >>>>        error: hwirq 0x4 is too large for dummy
> >>>>
> >>>> Fix this by using pci_irqd_intx_xlate() helper to translate the INTx 1-4
> >>>> range into the 0-3 as done in other PCIe drivers.
> >>>>
> >>>> Suggested-by: Bjorn Helgaas <bhelgaas@...gle.com>
> >>>> Reported-by: Chris Welch <Chris.Welch@...visolutions.com>
> >>>> Signed-off-by: Vignesh R <vigneshr@...com>
> >>>
> >>> Acked-by: Kishon Vijay Abraham I <kishon@...com>
> >>>> ---
> >>>>  drivers/pci/dwc/pci-dra7xx.c | 3 ++-
> >>>>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/drivers/pci/dwc/pci-dra7xx.c b/drivers/pci/dwc/pci-dra7xx.c
> >>>> index 58aed0896468..892f93910012 100644
> >>>> --- a/drivers/pci/dwc/pci-dra7xx.c
> >>>> +++ b/drivers/pci/dwc/pci-dra7xx.c
> >>>> @@ -226,6 +226,7 @@ static int dra7xx_pcie_intx_map(struct irq_domain *domain, unsigned int irq,
> >>>>  
> >>>>  static const struct irq_domain_ops intx_domain_ops = {
> >>>>  	.map = dra7xx_pcie_intx_map,
> >>>> +	.xlate = pci_irqd_intx_xlate,
> >>
> >> Looking at this again, I think the mapping should be done in device tree using
> >> the interrupt-map property.
> >>
> >> Lorenzo, can you hold merging this patch till we verify using the dt approach?
> > 
> > Yes and I agree that's a DT mapping bug.
> 
> I did some testing by changing interrupt-map property of PCIe node as as
> below:
> diff --git a/arch/arm/boot/dts/dra7.dtsi b/arch/arm/boot/dts/dra7.dtsi
> index 261b5deb2456..2b1a2c5303bb 100644
> --- a/arch/arm/boot/dts/dra7.dtsi
> +++ b/arch/arm/boot/dts/dra7.dtsi
> @@ -332,10 +332,10 @@
>                                 phys = <&pcie1_phy>;
>                                 phy-names = "pcie-phy0";
>                                 interrupt-map-mask = <0 0 0 7>;
> -                               interrupt-map = <0 0 0 1 &pcie1_intc 1>,
> -                                               <0 0 0 2 &pcie1_intc 2>,
> -                                               <0 0 0 3 &pcie1_intc 3>,
> -                                               <0 0 0 4 &pcie1_intc 4>;
> +                               interrupt-map = <0 0 0 1 &pcie1_intc 0>,
> +                                               <0 0 0 2 &pcie1_intc 1>,
> +                                               <0 0 0 3 &pcie1_intc 2>,
> +                                               <0 0 0 4 &pcie1_intc 3>;
> 
> 
> Although this eliminates need for xlate, we still need driver change to
> call the correct handler with above change:
> 
> static int dra7xx_pcie_init_irq_domain(struct pcie_port *pp)
> @@ -269,7 +270,7 @@ static irqreturn_t dra7xx_pcie_msi_irq_handler(int
> irq, void *arg)
>  	case INTC:
>  	case INTD:
>  		generic_handle_irq(irq_find_mapping(dra7xx->irq_domain,
> -						    ffs(reg)));
> +						    ffs(reg) - 1));
>  		break;
>  	}
> 
> 
> If we merge the driver change then the DT backward compatibility is
> broken. Right now INTA/B/C keep working even with buggy interrupt-map
> settings. But, if we fix  interrupt-map and merge above driver change,
> then we will be *breaking* DT backward compatibility and INTA/B/C will
> no longer work with older DTs.
> Therefore, IMO, this patch should be merged in order to keep DT backward
> compatibility and live with wrong DT representation.

Yes, this is a mess. I am not fond at all of this fix but I will end
up merging it for the same reasons you provided - I can't break
backward DT compatibility.

Lorenzo