Re: [PATCH v2 07/10] PCI: layerscape: Modify the MSIX to the doorbell way

[Kishon Vijay Abraham I]

Gustavo,

On 06/11/19 3:10 PM, Gustavo Pimentel wrote:
> On Thu, Aug 29, 2019 at 6:13:18, Kishon Vijay Abraham I <kishon@xxxxxx> 
> wrote:
> 
> Hi, this email slip away from my attention...
> 
>> Gustavo,
>>
>> On 27/08/19 6:55 PM, Andrew Murray wrote:
>>> On Sat, Aug 24, 2019 at 12:08:40AM +0000, Xiaowei Bao wrote:
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: Andrew Murray <andrew.murray@xxxxxxx>
>>>>> Sent: 2019å8æ23æ 21:58
>>>>> To: Xiaowei Bao <xiaowei.bao@xxxxxxx>
>>>>> Cc: bhelgaas@xxxxxxxxxx; robh+dt@xxxxxxxxxx; mark.rutland@xxxxxxx;
>>>>> shawnguo@xxxxxxxxxx; Leo Li <leoyang.li@xxxxxxx>; kishon@xxxxxx;
>>>>> lorenzo.pieralisi@xxxxxx; arnd@xxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; M.h.
>>>>> Lian <minghuan.lian@xxxxxxx>; Mingkai Hu <mingkai.hu@xxxxxxx>; Roy
>>>>> Zang <roy.zang@xxxxxxx>; jingoohan1@xxxxxxxxx;
>>>>> gustavo.pimentel@xxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
>>>>> devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
>>>>> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx
>>>>> Subject: Re: [PATCH v2 07/10] PCI: layerscape: Modify the MSIX to the
>>>>> doorbell way
>>>>>
>>>>> On Thu, Aug 22, 2019 at 07:22:39PM +0800, Xiaowei Bao wrote:
>>>>>> The layerscape platform use the doorbell way to trigger MSIX interrupt
>>>>>> in EP mode.
>>>>>>
>>>>>
>>>>> I have no problems with this patch, however...
>>>>>
>>>>> Are you able to add to this message a reason for why you are making this
>>>>> change? Did dw_pcie_ep_raise_msix_irq not work when func_no != 0? Or did
>>>>> it work yet dw_pcie_ep_raise_msix_irq_doorbell is more efficient?
>>>>
>>>> The fact is that, this driver is verified in ls1046a platform of NXP before, and ls1046a don't
>>>> support MSIX feature, so I set the msix_capable of pci_epc_features struct is false,
>>>> but in other platform, e.g. ls1088a, it support the MSIX feature, I verified the MSIX
>>>> feature in ls1088a, it is not OK, so I changed to another way. Thanks.
>>>
>>> Right, so the existing pci-layerscape-ep.c driver never supported MSIX yet it
>>> erroneously had a switch case statement to call dw_pcie_ep_raise_msix_irq which
>>> would never get used.
>>>
>>> Now that we're adding a platform with MSIX support the existing
>>> dw_pcie_ep_raise_msix_irq doesn't work (for this platform) so we are adding a
>>> different method.
>>
>> Gustavo, can you confirm dw_pcie_ep_raise_msix_irq() works for designware as it
>> didn't work for both me and Xiaowei?
> 
> When I implemented the dw_pcie_ep_raise_msix_irq(), the implementation 
> was working quite fine on DesignWare solution. Otherwise, I wouldn't 
> submit it to the kernel.
> From what I have seen and if I recall well, Xiaowei implementation was 
> done having PF's configurated on his solution, which is a configuration 
> that I don't have in my solution, I believe this could be the missing 
> piece that differs between our 2 implementations.

I haven't debugged the issue yet but in my understanding the MSI-X table should
be in the memory (DDR) of EP system. This table will be populated by RC while
configuring MSI-X (with msg address and msg data). The EP will use the
populated msg address and msg data for raising MSI-X interrupt.

>From the dw_pcie_ep_raise_msix_irq() (copied below), nowhere the MSI-X table is
being read from the memory of EP system. I've given my comments below.

int dw_pcie_ep_raise_msix_irq(struct dw_pcie_ep *ep, u8 func_no,
			     u16 interrupt_num)
{
	.
	.
	reg = PCI_BASE_ADDRESS_0 + (4 * bir);
	bar_addr_upper = 0;
	bar_addr_lower = dw_pcie_readl_dbi(pci, reg);

BAR register will hold the "PCI address" programmed by the host. So
"bar_addr_lower" will have PCI address.

	reg_u64 = (bar_addr_lower & PCI_BASE_ADDRESS_MEM_TYPE_MASK);
	if (reg_u64 == PCI_BASE_ADDRESS_MEM_TYPE_64)
		bar_addr_upper = dw_pcie_readl_dbi(pci, reg + 4);

	tbl_addr = ((u64) bar_addr_upper) << 32 | bar_addr_lower;

The "tbl_addr" now has the PCI address programmed by the host.

	tbl_addr += (tbl_offset + ((interrupt_num - 1) * PCI_MSIX_ENTRY_SIZE));
	tbl_addr &= PCI_BASE_ADDRESS_MEM_MASK;

	msix_tbl = ioremap_nocache(ep->phys_base + tbl_addr,
				   PCI_MSIX_ENTRY_SIZE);

"ep->phys_base" will have EPs outbound memory address and "tbl_addr" will have
PCI address. So msix_tbl points to the EPs outbound memory region.
	if (!msix_tbl)
		return -EINVAL;

	msg_addr_lower = readl(msix_tbl + PCI_MSIX_ENTRY_LOWER_ADDR);
	msg_addr_upper = readl(msix_tbl + PCI_MSIX_ENTRY_UPPER_ADDR);

Here an access to the EP outbound region is made (and the transaction will be
based on ATU configuration).
The message address should ideally be obtained from the MSI-X table present in
the EP system. There need not be any access to the OB region for getting data
from MSI-X table.

	msg_addr = ((u64) msg_addr_upper) << 32 | msg_addr_lower;
	msg_data = readl(msix_tbl + PCI_MSIX_ENTRY_DATA);
	vec_ctrl = readl(msix_tbl + PCI_MSIX_ENTRY_VECTOR_CTRL);

All this should be obtained from the memory of EP.
	.
	.
}

I'm not sure how this worked for you.

Thanks
Kishon

> 
> Since patch submission into the kernel related to msix feature on pcitest 
> tool, I didn't touch or re-tested the msix feature by lack of time (other 
> projects requires my full attention for now). However is on my roadmap to 
> came back to add some other features on DesignWare eDMA driver and I can 
> do at that time some tests to see if the 
> dw_pcie_ep_raise_msix_irq_doorbell() is compatible or not with my 
> solution. If so, I can do some patch to simplify and use the 
> dw_pcie_ep_raise_msix_irq_doorbell() if it still works as expected like 
> on dw_pcie_ep_raise_msix_irq(). Agree?
> 
> Gustavo
> 
>>
>> Thanks
>> Kishon
> 
>