Re: [PATCH] PCI: dw-rockchip: Skip waiting for link up

[Shawn Lin <shawn.lin@rock-chips.com>]

在 2025/10/21 星期二 12:26, FUKAUMI Naoki 写道:
> Hi Niklas, Bjorn,
> 
> I noticed an issue on the Rockchip RK3588S SoC using the ASMedia ASM2806 
> PCIe bridge where devices behind the bridge fail to probe since v6.14.
> Specifically, this started happening after commit 
> 647d69605c70368d54fc012fce8a43e8e5955b04.
> dmesg logs from before and after this commit are available at:
>   https://gist.github.com/RadxaNaoki/fca2bfca2ee80fefee7b00c7967d2e3d
> 
> I have confirmed that reverting the following commits fixes the issue:
>   commit ec9fd499b9c6 ("PCI: dw-rockchip: Don't wait for link since we 
> can detect Link Up")
>   commit 0e0b45ab5d77 ("PCI: dw-rockchip: Enumerate endpoints based on 
> dll_link_up IRQ")
> 

Then these two commits would like to reply on link up irq instead of
fixed delay in dwc framework. Here is a not very precise timeline
description.

time(ms) |  dw_pcie_wait_for_link（）     | sys irq_thread() | Hot reset
-------------------------------------------------------------------------
0:       |  dw_pcie_link_up return false  |  link up irq     |
1x       |  Physical link up happend      |                  |
90:      |  dw_pcie_link_up return true   |                  |
100:     |                                |  msleep(100) done|
10x:     |                                |  pci_rescan_bus  |
1xx:     |                                |                  | <==occur
190:     |  msleep(90) done               |                  |
19x:     |  pci_host_probe                |                  |

What if the hot reset happens when pci_rescan_bus() starts. I think
scan devices possible fail when seeing 0xffffffff from cfg read. But
a 90ms delay perfectly avoids this event in dw_pcie_wait_for_link(), and 
by the time the 90ms delay is completed, the link is actually in an
accessible state.

> On v6.18-rc2, the cold boot behavior has changed somewhat, and I have 
> observed the following three behaviors so far:
> 
> - Probe succeeds
> - Probe fails
> - Kernel oops
> 
> There seems to be no pattern to these three behaviors. During a warm 
> boot, a successful probe does not seem to occur.
> 
> If commit ec9fd499b9c6 is reverted on v6.18-rc2, I have observed the 
> following two behaviors so far:
> 
> - Probe succeeds
> - Kernel oops
> 
> "Probe fails" has not been observed so far.
> 
> The dmesg for the kernel oops is available at:
>   https://gist.github.com/RadxaNaoki/4b2dcd5e41b09004eda2fdeb80ae5e15
> 
> Can you please help me with this issue?
> 
> Best regards,
> 
> -- 
> FUKAUMI Naoki
> Radxa Computer (Shenzhen) Co., Ltd.
> 
> On 1/13/25 19:59, Niklas Cassel wrote:
>> The Root Complex specific device tree binding for pcie-dw-rockchip has 
>> the
>> 'sys' interrupt marked as required.
>>
>> The driver requests the 'sys' IRQ unconditionally, and errors out if not
>> provided.
>>
>> Thus, we can unconditionally set use_linkup_irq before calling
>> dw_pcie_host_init().
>>
>> This will skip the wait for link up (since the bus will be enumerated 
>> once
>> the link up IRQ is triggered), which reduces the bootup time.
>>
>> Signed-off-by: Niklas Cassel <cassel@kernel.org>
>> ---
>>   drivers/pci/controller/dwc/pcie-dw-rockchip.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>>
>> ---
>> base-commit: 2adda4102931b152f35d054055497631ed97fe73
>> change-id: 20250113-rockchip-no-wait-403ffbc42313
>>
>> Best regards,
>>
>> diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/ 
>> pci/controller/dwc/pcie-dw-rockchip.c
>> index 
>> 1170e1107508bd793b610949b0afe98516c177a4..62034affb95fbb965aad3cebc613a83e31c90aee 100644
>> --- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
>> +++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
>> @@ -435,6 +435,7 @@ static int rockchip_pcie_configure_rc(struct 
>> rockchip_pcie *rockchip)
>>       pp = &rockchip->pci.pp;
>>       pp->ops = &rockchip_pcie_host_ops;
>> +    pp->use_linkup_irq = true;
>>       return dw_pcie_host_init(pp);
>>   }
> 
> 
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