linux-kernel - Re: [PATCH net-next 3/3] r8169: disable RTL8126 ZRX-DC timeout

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Message-ID: <eeba10a2-809a-4583-bd35-1f363c824e14@gmail.com>
Date: Fri, 21 Feb 2025 21:12:09 +0100
From: Heiner Kallweit <hkallweit1@...il.com>
To: Bjorn Helgaas <helgaas@...nel.org>, ChunHao Lin <hau@...ltek.com>
Cc: nic_swsd@...ltek.com, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 3/3] r8169: disable RTL8126 ZRX-DC timeout

On 21.02.2025 21:01, Bjorn Helgaas wrote:
> On Fri, Feb 21, 2025 at 03:18:28PM +0800, ChunHao Lin wrote:
>> Disable it due to it dose not meet ZRX-DC specification. If it is enabled,
>> device will exit L1 substate every 100ms. Disable it for saving more power
>> in L1 substate.
> 
> s/dose/does/
> 
> Is ZRX-DC a PCIe spec?  A Google search suggests that it might not be
> completely Realtek-specific?
> 
ZRX-DC is the receiver DC impedance as specified in the PCIe Base Specification.
>From what I've found after a quick search ASPM restrictions apply if this impedance
isn't in the range 40-60 ohm.

>> +static void rtl_disable_zrxdc_timeout(struct rtl8169_private *tp)
>> +{
>> +	struct pci_dev *pdev = tp->pci_dev;
>> +	u8 val;
>> +
>> +	if (pdev->cfg_size > 0x0890 &&
>> +	    pci_read_config_byte(pdev, 0x0890, &val) == PCIBIOS_SUCCESSFUL &&
>> +	    pci_write_config_byte(pdev, 0x0890, val & ~BIT(0)) == PCIBIOS_SUCCESSFUL)
> 
> Is this a standard PCIe extended capability?  If so, it would be nice
> to search for it with pci_find_ext_capability() and use standard
> #defines.
> 
> Bjorn