Re: [RFC PATCH 1/9] PCI/AER: Update AER driver to call root port and downstream port UCE handlers

[Terry Bowman]

Hi Fan,

On 7/10/24 15:48, nifan.cxl@xxxxxxxxx wrote:
> On Mon, Jun 24, 2024 at 12:56:29PM -0500, Terry Bowman wrote:
>> Hi Dan,
>>
>> I added a response below.
>>
>> On 6/21/24 14:17, Dan Williams wrote:
>>> Terry Bowman wrote:
>>>> The AER service driver does not currently call a handler for AER
>>>> uncorrectable errors (UCE) detected in root ports or downstream
>>>> ports. This is not needed in most cases because common PCIe port
>>>> functionality is handled by portdrv service drivers.
>>>>
>>>> CXL root ports include CXL specific RAS registers that need logging
>>>> before starting do_recovery() in the UCE case.
>>>>
>>>> Update the AER service driver to call the UCE handler for root ports
>>>> and downstream ports. These PCIe port devices are bound to the portdrv
>>>> driver that includes a CE and UCE handler to be called.
>>>>
>>>> Signed-off-by: Terry Bowman <terry.bowman@xxxxxxx>
>>>> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>>>> Cc: linux-pci@xxxxxxxxxxxxxxx
>>>> ---
>>>>  drivers/pci/pcie/err.c | 20 ++++++++++++++++++++
>>>>  1 file changed, 20 insertions(+)
>>>>
>>>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>>>> index 705893b5f7b0..a4db474b2be5 100644
>>>> --- a/drivers/pci/pcie/err.c
>>>> +++ b/drivers/pci/pcie/err.c
>>>> @@ -203,6 +203,26 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>>>  	pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
>>>>  	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
>>>>  
>>>> +	/*
>>>> +	 * PCIe ports may include functionality beyond the standard
>>>> +	 * extended port capabilities. This may present a need to log and
>>>> +	 * handle errors not addressed in this driver. Examples are CXL
>>>> +	 * root ports and CXL downstream switch ports using AER UIE to
>>>> +	 * indicate CXL UCE RAS protocol errors.
>>>> +	 */
>>>> +	if (type == PCI_EXP_TYPE_ROOT_PORT ||
>>>> +	    type == PCI_EXP_TYPE_DOWNSTREAM) {
>>>> +		struct pci_driver *pdrv = dev->driver;
>>>> +
>>>> +		if (pdrv && pdrv->err_handler &&
>>>> +		    pdrv->err_handler->error_detected) {
>>>> +			const struct pci_error_handlers *err_handler;
>>>> +
>>>> +			err_handler = pdrv->err_handler;
>>>> +			status = err_handler->error_detected(dev, state);
>>>> +		}
>>>> +	}
>>>> +
>>>
>>> Would not a more appropriate place for this be pci_walk_bridge() where
>>> the ->subordinate == NULL and these type-check cases are unified?
>>
>> It does. I can take a look at moving that.
> 
> Has that already been handled in pci_walk_bridge?
> 
> The function pci_walk_bridge() will call report_error_detected, where
> the err handler will be called. 
> https://elixir.bootlin.com/linux/v6.10-rc6/source/drivers/pci/pcie/err.c#L80
> 
> Fan
> 

You would think so but the UCE handler was not called in my testing for the PCIe 
ports (RP,USP,DSP). The pci_walk_bridge() function has 2 cases:
- If there is a subordinate/secondary bus then the callback is called for
those downstream devices but not the port itself.
- If there is no subordinate/secondary bus then the callback is invoked for the 
port itself.

The function header comment may explain it better:
/**                                                                                                                                                                                                                
 * pci_walk_bridge - walk bridges potentially AER affected                                                                                                                                                         
 * @bridge:     bridge which may be a Port, an RCEC, or an RCiEP                                                                                                                                                   
 * @cb:         callback to be called for each device found                                                                                                                                                        
 * @userdata:   arbitrary pointer to be passed to callback                                                                                                                                                         
 *                                                             
 * If the device provided is a bridge, walk the subordinate bus, including                                                                                                                                         
 * any bridged devices on buses under this bus.  Call the provided callback                                                                                                                                        
 * on each device found.                                                                                                                                                                                           
 *                                                                                                                                                                                                                 
 * If the device provided has no subordinate bus, e.g., an RCEC or RCiEP,                                                                                                                                          
 * call the callback on the device itself. 
 */

Regards,
Terry

>>
>> Regards,
>> Terry