linux-kernel - Re: [PATCH v7] PCI: Xilinx-NWL-PCIe: Added support for Xilinx NWL PCIe Host Controller

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Message-ID: <563A1ECC.3000609@arm.com>
Date:	Wed, 04 Nov 2015 15:05:48 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	Michal Simek <michals@...inx.com>,
	Soren Brinkmann <sorenb@...inx.com>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"tinamdar@....com" <tinamdar@....com>,
	"treding@...dia.com" <treding@...dia.com>,
	"rjui@...adcom.com" <rjui@...adcom.com>,
	"Minghuan.Lian@...escale.com" <Minghuan.Lian@...escale.com>,
	"m-karicheri2@...com" <m-karicheri2@...com>,
	"hauke@...ke-m.de" <hauke@...ke-m.de>,
	"dhdang@....com" <dhdang@....com>,
	"sbranden@...adcom.com" <sbranden@...adcom.com>
CC:	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Ravikiran Gummaluri <rgummal@...inx.com>
Subject: Re: [PATCH v7] PCI: Xilinx-NWL-PCIe: Added support for Xilinx NWL
 PCIe Host Controller

On 04/11/15 12:30, Bharat Kumar Gogada wrote:
>>
>>>> Also, you still lack support for MSI-X (which would come for free...).
>>>
>>> We don't support MSI-X in root port mode.
>>
>> I don't believe you. If you support single MSI, you support MSI-X (because
>> that's mostly a property of the endpoint).
> 
> In our architecture specification MSI-X is unsupported for Root Port.

I still can't believe it, but in the end, that's your own problem.

>>>>> +	.chip = &nwl_msi_irq_chip,
>>>>> +};
>>>>> +#endif
>>>>> +
>>>>> +
>>>>> +	/* setup AFI/FPCI range */
>>>>> +	msi->pages = __get_free_pages(GFP_KERNEL, 0);
>>>>> +	base = virt_to_phys((void *)msi->pages);
>>>>> +	nwl_bridge_writel(pcie, lower_32_bits(base), I_MSII_BASE_LO);
>>>>> +	nwl_bridge_writel(pcie, upper_32_bits(base), I_MSII_BASE_HI);
>>>>
>>>> I just read this, and I'm puzzled. Actually, puzzled is an
>>>> understatement. Why on Earth do you need to give RAM to your MSI
>> HW?
>>>> This should be a device, not RAM. By the look of it, this could be
>>>> absolutely anything. Are you sure you have to supply RAM here?
>>>>
>>> This is required in our hardware, so that bridge identifies incoming MWr as
>> MSI.
>>
>> I'm asking why this has to be RAM. What is the actual requirement?
> 
> We are allocating RAM for MSI (which is expected) and assigning this address to msi->pages
> this is what EP MSI capability will be programmed with.
> For the bridge to detect an incoming MWr from EP as MSI, hardware needs to know MSI address
> so the same address is programmed in the hardware register for comparison purpose.
> It is the actual requirement from hardware.

I understand that you need to provide an address for the bridge to
match. I'm asking why this has to be RAM as opposed to any other device
address. This seems to be a unique requirement (nobody else does that),
and I'd like to understand why there is this requirement.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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