linux-kernel - Re: [PATCH] PCI: Check for PCIe downtraining conditions

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Date:   Thu, 31 May 2018 12:13:51 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     "Alex G." <mr.nuke.me@...il.com>, Alex_Gagniuc@...lteam.com,
        bhelgaas@...gle.com
Cc:     Austin.Bolen@...l.com, Shyam.Iyer@...l.com, keith.busch@...el.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: Check for PCIe downtraining conditions

On 5/31/2018 12:01 PM, Alex G. wrote:
>>       PCI: Add pcie_print_link_status() to log link speed and whether it's limited
> This one, I have, but it's not what I need. This looks at the available
> bandwidth from root port to endpoint, whereas I'm only interested in
> downtraining between endpoint and upstream port.

I see what you are saying. 

With a little bit of effort, you can reuse the same code.

Here is an attempt.

You can probably extend pcie_bandwidth_available() to put an optional parent bridge
device for your own use case and terminate the loop around here.

https://elixir.bootlin.com/linux/v4.17-rc7/source/drivers/pci/pci.c#L5182

Then, you can use the existing code to achieve what you are looking for via
pcie_print_link_status() by adding an optional parent parameter.

	bw_cap = pcie_bandwidth_capable(dev, &speed_cap, &width_cap);
	bw_avail = pcie_bandwidth_available(dev, &limiting_dev, &speed, &width, *parent*);

If parent parameter is NULL, code can walk all the way to root as it is doing today.
If it is not, then will terminate the loop on the first iteration.

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.