Re: [PATCH v2 9/9] PCI: rockchip: Add parameter check for RK3399 PCIe endpoint core set_msi()

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 2/21/23 22:19, Rick Wertenbroek wrote:
> On Tue, Feb 21, 2023 at 11:55 AM Damien Le Moal
> <damien.lemoal@opensource.wdc.com> wrote:
>>
>> On 2/21/23 19:47, Rick Wertenbroek wrote:
>>> On Wed, Feb 15, 2023 at 2:39 AM Damien Le Moal
>>> <damien.lemoal@opensource.wdc.com> wrote:
>>>>
>>>> On 2/14/23 23:08, Rick Wertenbroek wrote:
>>>>> The RK3399 PCIe endpoint core supports only a single PCIe physcial
>>>>> function (function number 0), therefore return -EINVAL if set_msi() is
>>>>> called with a function number greater than 0.
>>>>> The PCIe standard only allows the multi message capability (MMC) value
>>>>> to be up to 0x5 (32 messages), therefore return -EINVAL if set_msi() is
>>>>> called with a MMC value of over 0x5.
>>>>>
>>>>> Signed-off-by: Rick Wertenbroek <rick.wertenbroek@gmail.com>
>>>>> ---
>>>>>  drivers/pci/controller/pcie-rockchip-ep.c | 10 ++++++++++
>>>>>  1 file changed, 10 insertions(+)
>>>>>
>>>>> diff --git a/drivers/pci/controller/pcie-rockchip-ep.c b/drivers/pci/controller/pcie-rockchip-ep.c
>>>>> index b7865a94e..80634b690 100644
>>>>> --- a/drivers/pci/controller/pcie-rockchip-ep.c
>>>>> +++ b/drivers/pci/controller/pcie-rockchip-ep.c
>>>>> @@ -294,6 +294,16 @@ static int rockchip_pcie_ep_set_msi(struct pci_epc *epc, u8 fn, u8 vfn,
>>>>>       struct rockchip_pcie *rockchip = &ep->rockchip;
>>>>>       u32 flags;
>>>>>
>>>>> +     if (fn) {
>>>>> +             dev_err(&epc->dev, "This endpoint controller only supports a single physical function\n");
>>>>> +             return -EINVAL;
>>>>> +     }
>>>>
>>>> Checking this here is late... Given that at most only one physical
>>>> function is supported, the check should be in rockchip_pcie_parse_ep_dt().
>>>> Something like:
>>>>
>>>>         err = of_property_read_u8(dev->of_node, "max-functions",
>>>>                                   &ep->epc->max_functions);
>>>>
>>>>         if (err < 0 || ep->epc->max_functions > 1)
>>>>
>>>>                 ep->epc->max_functions = 1;
>>>>
>>>
>>> Yes, this could be moved to the probe, thanks.
>>>
>>>> And all the macros with the (fn) argument could also be simplified
>>>> (argument fn removed) since fn will always be 0.
>>>
>>> These functions cannot be simplified because they have to follow the signature
>>> given by "pci_epc_ops" (include/linux/pci-epc.h). And this signature has the
>>> function number as a parameter. If we change the function signature we won't
>>> be able to assign these functions to the pc_epc_ops structure
>>
>> I was not suggesting to change the functions signature. I was suggesting
>> dropping the fn argument for the *macros*, e.g.
>>
>> ROCKCHIP_PCIE_EP_FUNC_BASE(fn) -> ROCKCHIP_PCIE_EP_FUNC_BASE
>>
>> since fn is always 0.
>>
>> That said, I am not entirely sure if the limit really is 1 function at most. The
>> TRM seems to be suggesting that up to 4 functions can be supported...
>>
>> [...]
>>
>>>> Another nice cleanup: define ROCKCHIP_PCIE_EP_MSI_CTRL_REG to include the
>>>> ROCKCHIP_PCIE_EP_FUNC_BASE(fn) addition so that we do not have to do it
>>>> here all the time.
>>>
>>> Yes, this could be an improvement but this is the way it is written
>>> everywhere in this
>>> driver, I chose to keep it so as to remain coherent with the rest of the driver.
>>> Cleaning this is not so important since this code will not be
>>> rewritten / changed so
>>> often. But I agree that it might be nicer. But, on the other side if
>>> at some point
>>> support for virtual functions would be added, the offsets would need
>>> to be computed
>>> based on the virtual function number and the code would be written
>>> like it is now,
>>> so I suggest keeping this the way it is for now.
>>
>> Yes, sure, this can be cleaned later.
>>
>> A more pressing problem is the lack of support for MSIX despite the fact that
>> the controller supports that *and* advertize it as a capability. That is what
>> was causing my problem with the Linux nvme driver and my prototype nvme epf
>> function driver: the host driver was seeing MSIX support (1 vector supported by
>> default), and so was allocating one MSIX for the device probe. But on the EP
>> end, it is MSI or INTX only... Working on adding that to solve this issue.
>>
> 
> I have seen this too, the controller advertises the capability. However, the TRM
> (section 17.5.9) says that MSI-X is not supported (MSI / INTx only as you said).
> So the solution should be to modify the probe function of the endpoint
> controller
> so that the MSI-X capability would not be advertised, this should fix
> your problem.

Yep, that is what I did for now: write 0 in the capability ID of the MSIX
capability list entry. A cleaner solution would be to change the next entry
pointer of the entry preceding the MSIX entry. Will send a patch for that.

> 
> I wonder if one could still implement MSI-X because from the endpoint we would
> just need to implement it as a message (TLP) over PCIe (because the space for
> the vectors is allocated and written, so that part should be ok). I am
> not an expert
> on MSI-X, but the reason the endpoint cannot send them could be because MSI-X
> requires some fields in the PCIe header descriptor to be filled with values that
> cannot be set through the "desc0-3" registers of the RK3399 PCIe endpoint core.
> 
> Anyways, the endpoint should not advertise the MSI-X capabilities when it cannot
> send such interrupts. Once this is fixed you should be able to have your NVMe
> function running.
> 
> Regards.
> Rick
> 
> 
>> --
>> Damien Le Moal
>> Western Digital Research
>>

-- 
Damien Le Moal
Western Digital Research