linux-kernel - Re: [PATCH] PCI: iproc: Fix BCMA PCIe bus scanning regression

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Date:	Tue, 26 Jan 2016 14:39:06 -0800
From:	Ray Jui <rjui@...adcom.com>
To:	Bjorn Helgaas <helgaas@...nel.org>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Rafal Milecki <zajec5@...il.com>,
	Hante Meuleman <meuleman@...adcom.com>,
	Hauke Mehrtens <hauke@...ke-m.de>,
	<linux-kernel@...r.kernel.org>,
	<bcm-kernel-feedback-list@...adcom.com>,
	<linux-pci@...r.kernel.org>
Subject: Re: [PATCH] PCI: iproc: Fix BCMA PCIe bus scanning regression



On 1/26/2016 1:54 PM, Bjorn Helgaas wrote:
> On Tue, Jan 26, 2016 at 10:37:20AM -0800, Ray Jui wrote:
>> Hi Bjorn,
>>
>> On 1/26/2016 10:22 AM, Bjorn Helgaas wrote:
>>> Hi Ray,
>>>
>>> On Wed, Jan 20, 2016 at 02:55:10PM -0800, Ray Jui wrote:
>>>> Commit 943ebae781f5 ("PCI: iproc: Add PAXC interface support") causes
>>>> regression on EP device detection on BCMA based platforms. This patch
>>>> fixes the issue by allowing multiple devices to be configured on the
>>>> same bus, for all PAXB based child buses
>>>>
>>>> Reported-by: Rafal Milecki <zajec5@...il.com>
>>>> Fixes: 943ebae781f5 ("PCI: iproc: Add PAXC interface support")
>>>> Signed-off-by: Ray Jui <rjui@...adcom.com>
>>>> ---
>>>>   drivers/pci/host/pcie-iproc.c | 5 +++--
>>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/pci/host/pcie-iproc.c b/drivers/pci/host/pcie-iproc.c
>>>> index 5816bce..4627561 100644
>>>> --- a/drivers/pci/host/pcie-iproc.c
>>>> +++ b/drivers/pci/host/pcie-iproc.c
>>>> @@ -171,10 +171,11 @@ static inline void iproc_pcie_ob_write(struct iproc_pcie *pcie,
>>>>   }
>>>>
>>>>   static inline bool iproc_pcie_device_is_valid(struct iproc_pcie *pcie,
>>>> +					      unsigned int busnum,
>>>>   					      unsigned int slot,
>>>>   					      unsigned int fn)
>>>>   {
>>>> -	if (slot > 0)
>>>> +	if ((pcie->type == IPROC_PCIE_PAXC || busnum == 0) && slot > 0)
>>>>   		return false;
>>>>
>>>>   	/* PAXC can only support limited number of functions */
>>>
>>> I don't understand this.  Here's the whole function (with this patch
>>> applied):
>>>
>>>      static inline bool iproc_pcie_device_is_valid(struct iproc_pcie *pcie,
>>> 						  unsigned int busnum,
>>> 						  unsigned int slot,
>>> 						  unsigned int fn)
>>>      {
>>> 	    if ((pcie->type == IPROC_PCIE_PAXC || busnum == 0) && slot > 0)
>>> 		    return false;
>>>
>>> 	    /* PAXC can only support limited number of functions */
>>> 	    if (pcie->type == IPROC_PCIE_PAXC && fn >= MAX_NUM_PAXC_PF)
>>> 		    return false;
>>>
>>> 	    return true;
>>>      }
>>>
>>> This says:
>>>
>>>    - On bus 00, device 0 is the only valid device.  That seems
>>>      plausible because the devices on bus 00 are probably built-in to
>>>      the SoC.
>>>
>>>    - On PAXC-based systems, device 0 is the only valid device on *any*
>>>      bus.  Is that really true?  If there's any way to add a plug-in
>>>      card, this seems overly restrictive.
>>
>> Yah, PAXC is connected with one internal device within the SoC.
>> There's no connection brought out of the chip.
>>
>>>      PCIe devices are generally all device 0, but this would mean you
>>>      cannot plug in a PCIe-to-PCI bridge leading to a PCI device with a
>>>      non-zero device number.
>>>
>>>      I think it also means you could not plug in a PCIe device with ARI
>>>      enabled, because I think we store the upper 5 bits of the 8-bit
>>>      ARI function number in the PCI_SLOT bits.
>>>
>>>    - On PAXC-based systems, only functions 0, 1, 2, and 3 are valid
>>>      anywhere in the hierarchy.  I think this again restricts what what
>>>      cards can be plugged in.
>>
>> Yes, the internal device connected to PAXC supports 4 physical functions.
>>
>>> If iProc only supports devices built directly into the SoC, maybe
>>> these constraints are valid.  But if it supports any plugin or
>>> external devices, they don't seem to make sense.
>>
>> Correct. PAXC only connects to one built-in device, while PAXB can
>> support external EP devices.
>
> OK, thanks for confirming all that.
>
> Something looks wrong in iproc_pcie_map_cfg_bus().
> iproc_pcie_device_is_valid() returns true for device 00:00.1,
> but the "busno == 0" case in iproc_pcie_map_cfg_bus() doesn't
> use "fn".  So the function number is ignored?  That would mean
> there's no difference between 000:00.0, 00:00.1, 00:00.2,
> 00:00.3, etc.

Okay, I should add a check to make sure only function zero is accepted 
on bus 0.

>
> I think this would be clearer and less error-prone if
> iproc_pcie_device_is_valid() were folded directly into
> iproc_pcie_map_cfg_bus().

Okay. I'll get rid of 'iproc_pcie_device_is_valid' and fold all of these 
check into 'iproc_pcie_map_cfg_bus' and then send out patch v2 for review

> Bjorn
>

Thanks!

Ray