linux-kernel - Re: [PATCH V2 3/5] PCI: xilinx: Modifying AXI PCIe Host Bridge driver to work on both Zynq and Microblaze

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Message-ID: <56A78EFF.1010503@xilinx.com>
Date:	Tue, 26 Jan 2016 16:21:35 +0100
From:	Michal Simek <michal.simek@...inx.com>
To:	Arnd Bergmann <arnd@...db.de>,
	Michal Simek <michal.simek@...inx.com>
CC:	Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
	<bhelgaas@...gle.com>, <lorenzo.pieralisi@....com>,
	<paul.burton@...tec.com>, <yinghai@...nel.org>,
	<wangyijing@...wei.com>, <robh@...nel.org>,
	<russell.joyce@...k.ac.uk>, <sorenb@...inx.com>,
	<jiang.liu@...ux.intel.com>, <pawel.moll@....com>,
	<mark.rutland@....com>, <ijc+devicetree@...lion.org.uk>,
	<galak@...eaurora.org>, <devicetree@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	"Bharat Kumar Gogada" <bharatku@...inx.com>,
	Ravi Kiran Gummaluri <rgummal@...inx.com>
Subject: Re: [PATCH V2 3/5] PCI: xilinx: Modifying AXI PCIe Host Bridge driver
 to work on both Zynq and Microblaze

On 26.1.2016 13:11, Arnd Bergmann wrote:
> On Tuesday 26 January 2016 10:59:12 Michal Simek wrote:
>>>> diff --git a/drivers/pci/host/pcie-xilinx.c b/drivers/pci/host/pcie-xilinx.c
>>>> index 3e3757f..1981948 100644
>>>> --- a/drivers/pci/host/pcie-xilinx.c
>>>> +++ b/drivers/pci/host/pcie-xilinx.c
>>>> @@ -92,7 +92,12 @@
>>>>  #define ECAM_DEV_NUM_SHIFT          12
>>>>  
>>>>  /* Number of MSI IRQs */
>>>> -#define XILINX_NUM_MSI_IRQS         128
>>>> +#define XILINX_NUM_MSI_IRQS 128
>>>> +#ifdef CONFIG_ARM
>>>> +#define TOT_NR_IRQS         XILINX_NUM_MSI_IRQS
>>>> +#else
>>>> +#define TOT_NR_IRQS         (NR_IRQS + XILINX_NUM_MSI_IRQS)
>>>> +#endif
>>>
>>> Something looks wrong here in the microblaze variant. What does NR_IRQS
>>> have to do with it?
>>
>> Arnd: What was the story regarding NR_IRQS?
>> I remember some discussion about it but just forget.
>>
>> Default value in include/asm-generic/irq.h is 64.
>> Current value is 32 because microblaze primary interrupt controller is
>> axi_intc core which has up to 32 input lines.
> 
> The value in asm-generic is completely arbitrary, it's just something
> that happens to work for a number of the simpler architectures.
> 
> Traditionally, there is a a fixed NR_IRQS which defines the maximum
> number of interrupts that can be used, and each irqchip has a fixed
> start offset below that number.
> 
> On modern systems, you have CONFIG_SPARSE_IRQ, which lets an irqchip
> allocate its own interrupts, without an upper limit. This is more
> flexible and avoids preallocating space for all irq_desc instances,
> so it saves memory.

ok. That was the story. I will look if there is any issue to enable
SPARSE_IRQ for Microblaze.

I also need to move intc driver out of arch.

Thanks,
Michal