linux-kernel - Re: [PATCH v3 1/3] PCI: Configure root port MPS during host probing

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Message-ID: <2ae86e9f-2a91-476a-b017-e0e20489d8da@163.com>
Date: Wed, 7 May 2025 22:55:28 +0800
From: Hans Zhang <18255117159@....com>
To: Niklas Cassel <cassel@...nel.org>
Cc: lpieralisi@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
 heiko@...ech.de, manivannan.sadhasivam@...aro.org, yue.wang@...ogic.com,
 pali@...nel.org, neil.armstrong@...aro.org, robh@...nel.org,
 jingoohan1@...il.com, khilman@...libre.com, jbrunet@...libre.com,
 martin.blumenstingl@...glemail.com, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-amlogic@...ts.infradead.org, linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v3 1/3] PCI: Configure root port MPS during host probing



On 2025/5/7 15:38, Niklas Cassel wrote:
> On Wed, May 07, 2025 at 01:34:37AM +0800, Hans Zhang wrote:
> 
> (snip)
> 
>>   static void pci_configure_mps(struct pci_dev *dev)
>>   {
>>   	struct pci_dev *bridge = pci_upstream_bridge(dev);
>> @@ -2178,6 +2209,10 @@ static void pci_configure_mps(struct pci_dev *dev)
>>   		return;
>>   	}
> 
> We should probably add a comment explaining why we are doing this here.
> 
> Perhaps something like:
> 
> /*
>   * Unless MPS strategy is PCIE_BUS_TUNE_OFF (don't touch MPS at all),
>   * start off by setting root ports' MPS to MPSS. Depending on the MPS
>   * strategy, and the MPSS of the devices below the root port, the MPS
>   * of the root port might get overriden later.
>   */
> 
> 

Dear Niklas,

Thank you very much for your reply and suggestions.
It will be added in the next version.

Best regards,
Hans

>> +	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT &&
>> +	    pcie_bus_config != PCIE_BUS_TUNE_OFF)
>> +		pcie_write_mps(dev, 128 << dev->pcie_mpss);
>> +
>>   	if (!bridge || !pci_is_pcie(bridge))
>>   		return;
>>   
> 
> 
> Kind regards,
> Niklas