Re: [PATCH v8] PCI: Xilinx-NWL-PCIe: Added support for Xilinx NWL PCIe Host Controller

[Marc Zyngier <marc.zyngier@arm.com>]

On 17/11/15 13:27, Bharat Kumar Gogada wrote:
>>
>> On Tue, 17 Nov 2015 04:59:39 +0000
>> Bharat Kumar Gogada <bharat.kumar.gogada@xilinx.com> wrote:
>>
>>>> On 11/16/2015 7:14 AM, Marc Zyngier wrote:
>>>>> On 11/11/15 06:33, Bharat Kumar Gogada wrote:
>>>>>> Adding PCIe Root Port driver for Xilinx PCIe NWL bridge IP.
>>>>>>
>>>>>> Signed-off-by: Bharat Kumar Gogada <bharatku@xilinx.com>
>>>>>> Signed-off-by: Ravi Kiran Gummaluri <rgummal@xilinx.com>
>>>>>> ---
>>>>>> Added logic to allocate contiguous hwirq in nwl_irq_domain_alloc
>>>> function.
>>>>>> Moved MSI functionality to separate functions.
>>>>>> Changed error return values.
>>>>>> ---
>>>>>>   .../devicetree/bindings/pci/xilinx-nwl-pcie.txt    |   68 ++
>>>>>>   drivers/pci/host/Kconfig                           |   16 +-
>>>>>>   drivers/pci/host/Makefile                          |    1 +
>>>>>>   drivers/pci/host/pcie-xilinx-nwl.c                 | 1062
>>>> ++++++++++++++++++++
>>>>>>   4 files changed, 1144 insertions(+), 3 deletions(-)
>>>>>>   create mode 100644
>>>>>> Documentation/devicetree/bindings/pci/xilinx-nwl-
>>>> pcie.txt
>>>>>>   create mode 100644 drivers/pci/host/pcie-xilinx-nwl.c
>>>>>>
>>>>>
>>>>> [...]
>>>>>
>>>>>> +static int nwl_pcie_enable_msi(struct nwl_pcie *pcie, struct
>>>>>> +pci_bus
>>>>>> +*bus) {
>>>>>> +	struct platform_device *pdev = to_platform_device(pcie-
>>> dev);
>>>>>> +	struct nwl_msi *msi = &pcie->msi;
>>>>>> +	unsigned long base;
>>>>>> +	int ret;
>>>>>> +
>>>>>> +	mutex_init(&msi->lock);
>>>>>> +
>>>>>> +	/* Check for msii_present bit */
>>>>>> +	ret = nwl_bridge_readl(pcie, I_MSII_CAPABILITIES) &
>> MSII_PRESENT;
>>>>>> +	if (!ret) {
>>>>>> +		dev_err(pcie->dev, "MSI not present\n");
>>>>>> +		ret = -EIO;
>>>>>> +		goto err;
>>>>>> +	}
>>>>>> +
>>>>>> +	/* Enable MSII */
>>>>>> +	nwl_bridge_writel(pcie, nwl_bridge_readl(pcie,
>> I_MSII_CONTROL) |
>>>>>> +			  MSII_ENABLE, I_MSII_CONTROL);
>>>>>> +
>>>>>> +	/* Enable MSII status */
>>>>>> +	nwl_bridge_writel(pcie, nwl_bridge_readl(pcie,
>> I_MSII_CONTROL) |
>>>>>> +			  MSII_STATUS_ENABLE, I_MSII_CONTROL);
>>>>>> +
>>>>>> +	/* 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);
>>>>>
>>>>> BTW, you still haven't answered my question as to why you need to
>>>>> waste a page of memory here, and why putting a device address
>>>>> doesn't
>>>> work.
>>>>>
>>>>> As this is (to the best of my knowledge) the only driver doing so,
>>>>> I'd really like you to explain the rational behind this.
>>>>
>>>> Might not be the only driver doing so after I start sending out
>>>> patches for the iProc MSI support (soon), :)
>>>>
>>>> I'm not sure how it works for the Xilinx NWL controller, which
>>>> Bharat should be able to help to explain. But for the iProc MSI
>>>> controller, there's no device I/O memory reserved for MSI posted writes
>> in the ASIC.
>>>> Therefore one needs to reserve host memory for these writes.
>>>>>
>>>
>>> Our SoC doesn't reserve any memory for MSI, hence we need to assign a
>>> memory space for it out of RAM.
>>
>> Question to both of you: Does the write make it to memory? Or is it sampled
>> by the bridge and dropped?
>>
> No, write will not do any modification in memory, it is consumed by bridge.

Then you do not need to allocate memory at all. Use whatever memory you
already have. CC-ing Robin, as this may have interaction with the SMMU.

> 
>> What happens if you replace the page in RAM with a dummy address?
> What do you mean by dummy address ?

Any random (and suitably aligned) address. 0x00000deadbeef000 for example.

Thanks,

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