Re: [PATCH v3 3/3] PCI: aardvark: Remove redundant MPS configuration

[Hans Zhang <18255117159@163.com>]

On 2025/5/7 01:41, Pali Rohár wrote:
> On Wednesday 07 May 2025 01:34:39 Hans Zhang wrote:
>> The Aardvark PCIe controller enforces a fixed 512B payload size via
>> PCI_EXP_DEVCTL_PAYLOAD_512B, overriding hardware capabilities and PCIe
>> core negotiations.
>>
>> Remove explicit MPS overrides (PCI_EXP_DEVCTL_PAYLOAD and
>> PCI_EXP_DEVCTL_PAYLOAD_512B). MPS is now determined by the PCI core
>> during device initialization, leveraging root port configurations and
>> device-specific capabilities.
>>
>> Aligning Aardvark with the unified MPS framework ensures consistency,
>> avoids artificial constraints, and allows the hardware to operate at
>> its maximum supported payload size while adhering to PCIe specifications.
>>
>> Signed-off-by: Hans Zhang <18255117159@163.com>
>> ---
>>   drivers/pci/controller/pci-aardvark.c | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
>> index a29796cce420..d8852892994a 100644
>> --- a/drivers/pci/controller/pci-aardvark.c
>> +++ b/drivers/pci/controller/pci-aardvark.c
>> @@ -549,9 +549,7 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
>>   	reg = advk_readl(pcie, PCIE_CORE_PCIEXP_CAP + PCI_EXP_DEVCTL);
>>   	reg &= ~PCI_EXP_DEVCTL_RELAX_EN;
>>   	reg &= ~PCI_EXP_DEVCTL_NOSNOOP_EN;
>> -	reg &= ~PCI_EXP_DEVCTL_PAYLOAD;
>>   	reg &= ~PCI_EXP_DEVCTL_READRQ;
>> -	reg |= PCI_EXP_DEVCTL_PAYLOAD_512B;
>>   	reg |= PCI_EXP_DEVCTL_READRQ_512B;
>>   	advk_writel(pcie, reg, PCIE_CORE_PCIEXP_CAP + PCI_EXP_DEVCTL);
>>   
>> -- 
>> 2.25.1
>>
> 
> Please do not remove this code. It is required part of the
> initialization of the aardvark PCI controller at the specific phase,
> as defined in the Armada 3700 Functional Specification.
> 
> There were reported more issues with those Armada PCIe controllers for
> which were already sent patches to mailing list in last 5 years. But
> unfortunately not all fixes were taken / applied yet.

Hi Pali,

I replied to you in version v2.

Is the maximum MPS supported by Armada 3700 512 bytes? What are the 
default values of DevCap.MPS and DevCtl.MPS?

Because the default value of DevCtl.MPS is not 512 bytes, it needs to be 
configured here, right?

If it's my guess, RK3588 also has the same requirements as you, just 
like the first patch I submitted.

Please take a look at the communication history:
https://patchwork.kernel.org/project/linux-pci/patch/20250416151926.140202-1-18255117159@163.com/

Please test it using patch 1/3 of this series. If there are any 
problems, please let me know.


Best regards,
Hans